New Trucks for Greater Productivity and Less Road Wear An Evaluation of the Turner Proposal -- Special Report 227 (1990) / Chapter Skim
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Committee for the Study of Relationships Between Vehicle Configurations and Highway Design MICHAEL WALTON, Chairman, University of Texas at Austin Joi-m R BILLING, Ontario Ministry of Transportation, Downsview GARLAND CHOW, University of British Columbia, Vancouver FORREST M
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Preface The American Association of State Highway and Transportation Officials asked the Transportation Research Board to evaluate proposals for new approaches to regulation of the size and weight of trucks using U.S. roads.
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that is, truck operators would be offered the choice of either continuing with existing equipment and weight rules or adopting the new trucks with the new weight regulations. Joseph R
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Contents Executive Summary . 1 1 Introduction.............................................
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6 Pavements . 157 Pavement Wear Model, 158 Pavement Impact Analysis, 160 Sensitivity Analysis, 171 7 Conclusions and Recommendations ........................179 Costs and Benefits of Introducing Turner Trucks, 179 Overall Evaluation, 195 Recommendations, 197 Appendix A Looking Ahead from Milepost 1984 at the Federal-Aid Highway Program........................................213 Francis C
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Executive Summary jn a 1984 address to the American Association of State Highway and Transportation Officials (AASHTO) , former Federal Highway Ad-ministrator Francis C
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NEW TRUCKS FOR GREATER PRoDucTIvITY AND LESS ROAD WEAR productivity. Truck users would gain productivity by operating trucks that exceed the current federal maximum of 80,000 lb.
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Executive Summary multitrailer combination has twin trailers, each 28 ft long, five axles, a maximum weight of 80,000 lb, and an overall length of about 70 ft; and longer doubles are used in a few states (Figure ES-i)
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SEVEN-AXLE TRACTOR-SEMITRAILER FIVE-AXLE TRACTOR-SEMITRAILER P067- 1JO-0 P Lac NINE-AXLE DOUBLE FIVE-AXLE TWIN TRAILER NINE-AXLE B-TRAIN DOUBLE NINE-AXLE TURNPIKE DOUBLE ELEVEN-AXLE DOUBLE FIGURE ES-i Left: Turner prototypes; right: selected trucks in use today.
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Executive Summary Safety and Traffic If no special measures were taken to improve its safety, the Turner double-trailer prototype with a single-drawbar dolly would have an accident rate slightly worse than that of the five-axle tractor-semitrailer it would replace and equal to or slightly better than that of the five-axle twin trailers replaced when operated under identical conditions. There would be no significant difference in accident rates for the Turner tractorsemitrailer prototype compared with existing tractor-semitrailers.
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NEW TRUCKS FOR GREATER PRoDucTiviTy AND LESS ROAD WEAR cost $2.8 billion. The change in the number of bridges on the nonprimary system not meeting the criteria would be 19,000, or 6 percent of the total.
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Executive Summary Less Than Nationwide Adoption Some states probably would choose initially not to allow use of the Turner trucks. Nevertheless, these trucks would still produce benefits if employed in only a few states or within one region.
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NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR major roads. Therefore, if a consensus in favor of the proposal formed among the states, it would be necessary for them to seek from Congress a nationwide coordinated Turner truck policy removing federal regulatory barriers for those states that wish to adopt these trucks.
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Executive Summary receive the pavement cost savings, a sharing of cost savings might be necessary. In addition to examining the costs and benefits of the proposal within its borders, a state must consider it alongside other options for reforming size and weight regulations that the committee did not evaluate and that could be adopted in addition to or instead of the Turner Proposal.
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10 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR Weight, Dimensions, and Equipment States introducing Turner trucks should adopt changes to existing regulations to allow operation of trucks that satisfy the restrictions given in Table ES-i regarding weight, dimensions, configuration, and equipment. Definitions and format for the restrictions should be consistent with those of TABLE ES-i RECOMMENDED TURNER VEHICLE RESTRICTIONS Parameter Restriction Weight (lb.)
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Executive Summary 11 the most recent revision of the AASHTO guide for dimensions and weights (AASHTO 1987)
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12 NEW TRUCKS FOR GREATER PRoDucrlvrry AND LESS ROAD WEAR quacy of roads to accommodate these trucks. A mechanism should be established for industry and government to resolve routing problems.
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Executive Summary 13 to direct the U.S. Department of Transportation to adopt standards constituting a federal definition of Turner trucks and to enact legislation providing that, in states that have adopted Turner truck regulations consistent with the federal definition, truck operations in compliance with those state regulations be allowed.
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14 NEW TRUCKS FOR GREATER PRoDucTIvrrY AND LESS ROAD WEAR congressional action setting relative program category funding levels that reflect the need for accelerated bridge spending in the early years after adoption of Turner trucks. Accelerated bridge spending in the first years of the federal-aid program would be compensated by reduced need for pavement repair in the later years.
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1 Introduction A11 states, as well as the federal government, regulate the size and weight of trucks allowed on public roads. The regulations are intended to balance the economic benefits of efficient freight transportation against the costs that large trucks can impose in the form of road wear, exposure to the risk of accidents, requirements on the geometric layout of roads and bridges, and interference with the movement of other traffic.
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16 NEW TRUCKS FOR GREATER PRoDucrIvIl'Y AND LESS ROAD WEAR an optimization perspective, which would couple productivity increases with basic vehicle design improvements as positive means to mitigate both road wear and accident hazards associated with large trucks. Uncertainty about the safety of larger trucks is probably the crucial obstacle to attaining the economic benefits of improved freight efficiency.
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Introduction 17 trator Francis C Turner (see Appendix A)
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18 NEW TRUCKS FOR GREATER PRoDuCTIvITY AND LESS ROAD WEAR trated on a proposal that contains a fundamental alteration of Turner's original concept: rather than Turner's mandatory change applying to all trucks with limited exceptions, it considered a voluntary system in which each truck operator would choose whether to comply with the new weight regulations or to continue to follow the previously existing rules. This change was adopted from the recommendation of the preliminary analysis of the Turner Proposal (NCHRP 1986)
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Introduction 19 and truck manufacturers; from cost analyses; and from examination of experience in jurisdictions that have implemented regulatory changes with some features of the Turner Proposal. The effects of the predicted use of the new trucks on the condition of road pavements and on road maintenance and construction costs were estimated.
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20 NEW TRUCKS FOR GREATER PRODUCrIvrrY AND LESS ROAD WEAR AASHTO.
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2 Background and Policy Options The historical background that establishes the rationale for the Turner Proposal is described first: trends in highway condition and finance, in the economic importance of trucking, and in regulation of truck size and weight. Next, earlier analysis of the proposal is summarized and the specific concerns regarding effects of the proposal on safety, highway costs, and freight productivity that were evaluated in the study are outlined.
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22 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR Although more and bigger trucks exacerbate highway maintenance problems, they also provide a service vital to the economy. The value of the added freight productivity from allowing at least moderately larger trucks usually is greater than the added costs that would be required to maintain road conditions with the increased loads.
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Background and Policy Options 23 TABLE 2-1 PAVEMENT CONDITION ON RURAL ARTERIAL ROADS, 1975-1987 (DOT 1981-1989) Mileage (%)
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24 NEW TRUCKS FOR GREATER PRoDUcrlvrry AND LESS ROAD WEAR TABLE 2-2 TRAFFIC VOLUMES ON RURAL INTERSTATES, 1978-1988 (FHWA 1978-1988) Billions of Annual Vehicle-Miles Year Combination Trucks All Motor Vehicles 1988 28 181 1987 27 170 1986 27 160 1985 26 154 1984 25 149 1983 23 145 1982 23 142 1981 22 139 1980 21 135 1979 21 136 1978 20 138 long-run growth rate is lower.
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Background and Policy Options 25 TABLE 2-3 PAVEMENT WEAR IMPACT OF TRAFFIC ON THE RURAL INTERSTATES, 1978-1988 (FHWA 1978-1988) Average Daily Equivalent Single- Axle Loadings Combinations with Year Five or More Axles All Vehicles 1988 5,100 5,500 1987 4,900 5,300 1986 4,600 5,000 1985 4,400 4,800 1984 3,900 4,300 1983 3,800 4,100 1982 3,800 4,300 1981 3,700 4,100 1980 3,700 4,100 1979 3,600 4,100 1978 3,300 3,700 Nom: The estimates in this table were not derived by a method consistent with that used for the esti- mates in Table 2-2, so year-to-year changes are not comparable between the two tables.
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26 NEW TRUCKS FOR GREATER PRonucrIvin' AND LESS ROAD WEAR Trends in Bridge Condition and Expenditures Although highway agencies have been able to keep up with pavement deterioration in recent years, efforts to maintain bridge condition have been less successful (Table 2-5)
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Background and Policy Options 27 Economic Importance of the frucking Industry The Turner Proposal was motivated not only by a desire to slow road wear, but also by recognition of the great economic value of productivity improvements in the trucking industry. Trucking is the principal freight transportation mode in the United States, in terms of the cost of its services.
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28 NEW TRUCKS FOR GREATER PRoDUcrrlvrrY AND LESS ROAD WEAR were authorized by Congress in 1982, $500 million in annual savings was predicted from the extended use of these trucks, even though they were expected to account for only a tenth of intercity combination-truck travel. A comprehensive 1981 U.S.
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Background and Policy Options 29 PRELIMINARY STUDY Presentation of the Turner Proposal at the 1984 AASHTO annual meeting attracted immediate attention. However, it was recognized that many questions would have to be answered about the impacts of the proposal on bridges, highway design requirements, safety, and motor carrier productivity before any consideration could be given to implementing such a fundamental change in size and weight regulations.
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30 NEW TRUCKS FOR GREATER PRODuCTIvITY AND LESS ROAD WEAR The preliminary study also considered a policy of building or rebuilding heavier, more durable pavements as an alternative that might also make operation of heavier trucks feasible while keeping pavement costs and performance under control. If strengthening pavements were relatively cheap and easy, it might make sense to undertake the extra increment of expense for this method of accommodating existing and heavier trucks, and dispense with the axle weight reductions of the Turner Proposal.
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Background and Policy Options 31 Allowing heavier and longer trucks, with the existing or even greater axle load limits, as well as a road investment program to strengthen pavements and bridges. This alternative is supported by the large positive benefit-cost ratios estimated in the earlier truck size and weight studies in which the freight savings of larger trucks were compared with the added highway construction and repair costs they would cause.
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32 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LESS Ron WEAR Controlling road wear through redesign of truck components must also deal with technical obstacles before it can be applied extensively, and ultimately it could be expected to have only limited effectiveness in increasing road capacity for larger trucks. This alternative would entail costs to truck operators and would require new regulations to certify components.
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TABLE 2-7 PROTOTYPE TRUCK CHARACTERISTICS LL -iLL ILILL LL I 0000 000 0 00 0000 00 0 00 00000 000 0 00 0000 00 Seven-Axle Nine-Axle Characteristic Tractor-Semitrailer Nine-Axle Double 11-Axle Double B-Train Double Dimensions Overall length (ft) Trailer length (ft)
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34 NEW TRUCKS FOR GREATER PRoDucrlvrrY AND LESS ROAD WEAR The 7-axle tractor-semitrailer, a tractor with three rear axles and a semitrailer with three axles; The 9-axle double, a tractor with tandem rear axles and two tandemaxle semitrailers coupled by a tandem-axle dolly of either the singledrawbar or double-drawbar design (Figure 2-1) ; The 11-axle double, a tandem-axle tractor and two 3-axle semitrailers; and The 9-axle B-train double, a tandem-axle tractor, a 4-axle semitrailer with a fifth wheel permanently affixed at the rear of its frame, and a tandem-axle semitrailer (Figure 2-1)
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Single-Drawbar Dolly Double-Drawbar Dolly B-Train FIGURE 2-1 Multiple-trailer hitching mechanisms (RTAC 1986)
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Path of outside front tractor tire actor / / / / ' Path of inside rear trailer tire Tractor-semitrailer Twin trailer truck FIGURE 2-2 Offtracking in a 90-degree turn at low speed (TRB 1986)
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Background and Policy Options 37 low-speed turning maneuvers. An offtracking performance criterion was imposed in defining the prototypes in recognition of the objective of the Turner Proposal to introduce new trucks that would be generally useful in a wide range of trucking applications on all roads nationwide now commonly carrying combination trucks.
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TABLE 2-8 BASELINE TRUCK CHARACTERISTICS LE:== Cl==jJ= c) 0 00 0000 oo Five-Axle Tractor-Semi- Five-Axle Twin Characteristic trailer Trailer Nine-Axle Turnpike Double Dimensions Overall length (ft)
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Gross weight under typi- cal current limits 80 80 120 Payload under typical limits 50 50 76 Tractor Conventional Conventional Conventional Trailer Flatbed, van, Flatbed, van, Flatbed, van, bulk bulk bulk Tires" (no. on loaded axles)
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SEVEN-AXLE TRACTOR-SEMITRAILER 48.0ft H 38.7ft -- I H- 1.0 ft 2.0 ft -I H- 4.3 ft 4.3 ft 12.0 ft-.
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F'- 9.0 ft -"-I F'- 4.3 ft F'-12.0 ft-_-.1 4.3 ft NINE-AXLE B-TRAIN DOUBLE F' 33.Oft F' 34.5 ft F'- 2.0 ft 33.Oft I I F' 25.8ft i0.f 2.0 ft - 4.3 ft -.1 F'- 4.3 ft -•1 I- 4.3 ft 12.0 ft -.' ELEVEN-AXLE DOUBLE F' 33.0ff •1 F' 33.0ft '-1 FIGURE 2-3 Midpoint dimensions of prototype vehicles.
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FIVE-AXLE TRACTOR-SEMITRAILER 48.0 or 45.0 ft 40.8 or 37.8ft .
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NINE-AXLE TURNPIKE DOUBLE 45.0 it I-. 45.0ft -I 36.8 it 36.8 it - 1I.-1.0 ft 3.0 it -4•'- 0.0 it 3.0 it -1 I..- 4.3 it - 4.3 it 4.3 it 12.0 it -.' 9.0 it -.4 F- 4.3 it FIGURE 2-4 Midpoint dimensions of baseline vehicles.
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44 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR For the impact analyses in the following chapters, these characteristics have been specified to reflect the requirements imposed by the regulatory options being evaluated and the preferences expressed by motor carriers and manufacturers in the interviews that were conducted to determine market acceptance of the prototype trucks. It was necessary to analyze a range of values for the major features in order to estimate the sensitivities of costs and benefits to the dimensions, weights, and component features selected.
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Background and Policy Options 45 REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Transportation Officials DOT U.S. Department of Transportation FHWA Federal Highway Administration NCHRP National Cooperative Highway Research Program RTAC Roads and Transportation Association of Canada TRB Transportation Research Board AASHTO.
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3 Use and hoductivity I f size and weight regulations were enacted that allowed use of Turner trucks, carriers would apply them where they could provide freight carriage service at a lower unit cost than can existing equipment. Existing trucks would continue to be applied where the added capacity of Turner trucks was not of sufficient practical benefit to offset the higher operating cost per truck-mile.
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Use and Productivity 47 need to know whether their maintenance costs would indeed decline under the proposal, what road classes and regions would feel the effects the most, and the timing of the changes. The use and productivity forecasts are based on four sources of information: A review of past analyses of the effects of changes in size and weight regulations on truck travel and costs.
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48 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR alternative configurations, because cost differences will determine the extent of use. The market potential for Turner trucks is described next, and the volume of Turner truck traffic and traffic lost by other trucks and rail is projected.
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Use and Productivity 49 best. Most of the studies did not deal well with changes in freight-handling or logistics costs.
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50 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR OPERATING COST COMPARISON The difference between the cost of moving freight in the combination trucks used nationwide today and the cost in the Turner prototypes is considered in three steps: Estimates are presented of operating costs per truck-mile and per ton-mile for existing trucks and Turner prototypes. The effects on relative total costs of the special operating characteristics of double-trailer configurations are described.
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Use and Productivity 51 Fuel: all fuel to power the truck and auxiliary equipment (e.g., refrigeration) , including fuel taxes.
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52 NEW TRUCKS FOR GREATER PRoDucrlvrrY AND LESS ROAD WEAR TABLE 3-1 TYPICAL OPERATING COSTS REPORTED IN CARRIER INTERVIEWS AND OTHER SOURCES FHWA • (Sydec, Inc. Carrier Interviews 1989)
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Use and Productivity 53 configuration operated in the same fleet, which can more reasonably be compared (Table 3-2)
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TABLE 3-2 DIFFERENCE IN OPERATING COSTS PER TRUCK-MILE BETWEEN FIVE-AXLE TRACTOR-SEMITRAILER AND LARGER COMBINATION Carrier Interviews Five-Axle Tractor- Larger Difference, FHWAb - Semitrailer Combination Difference . (Sydec, Inc.
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Use and Productivity 55 TABLE 3-3 OPERATING COSTS PER TRUCK-MILE FOR TURNER PROTOTYPES AND BASELINE TRUCKS Operating Costs" ($/mi) Maximum Van Body Tank Body GVW Fully Fully (Ib)
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56 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR other shipments on the same truck or when there are multiple pickup and delivery points at the beginning and end of trips. For travel partially loaded, greater capacity is of no advantage, and the carrier can expect that partially loaded mileage would be unchanged or would even increase if larger trucks were adopted.
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TABLE 3-4 AVERAGE LOAD AND OPERATING COSTS PER TONMILE FOR BASELINE TRUCKS AND TURNER PROTOTYES BEFORE ACCOUNTING FOR LOGISTICAL INEFFICIENCIES OF PROTOTYES Baseline Trucks Prototypes 5-Axle 7-Axle Tractor- 5-Axle 9-Axle 7-Axle 1 1-Axle Tractor- Truck Type Semitrailer Double Double Double Double Semitrailer High-Density Truckload Van Empty weight (Ib)
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58 NEW TRUCKS FOR GREATER PRODUCFIvrrY AND LESS ROAD WEAR TABLE 3-5 AVERAGE LOAD AND OPERATING COSTS PER TON- MILE FOR BASELINE TRUCKS AND TURNER PROTOTYPES AFTER ACCOUNTING FOR LOGISTICAL INEFFICIENCIES OF PROTOTYPES Baseline Prototypes Truck (5-Axle 7-Axle Tractor- 9-Axle 7-Axle 11-Axle Tractor- Truck 1ipe Semitrailer) Double Double Double Semitrailer High-Density Truckload Van Max.
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Use and Productivity 59 Secure facilities for trailers: Many applications in which doubles are popular [e.g., for less-than-truckload (LTL) freight]
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60 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR ing that emphasizes building traffic density in heavily traveled lanes. This advantage is eroded if the carrier must split traffic in a lane between two incompatible types of truck.
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Use and Productivity 61 (TRB 1986) , several carriers reported costs for expanding the number of doors at terminals to handle the additional trailers efficiently.
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62 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR fects) over a tractor-semitrailer.
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Use and Productivity 63 Turner trucks that may alter the cost per ton-mile from the estimates presented above include the following: Downsizing of axles, suspensions, brakes, and wheels to match them with axle loads, reducing initial cost and empty weight and thus increasing payload capacity; Use of single tires instead of dual tires on some or all axles to reduce tire costs and weight and increase payload capacity; Use of lift axles or steerable axles on trailers or dollies to reduce tire wear and lateral pavement forces or improve handling; Regulatory requirements to improve safety, including requirements on brakes, dolly design, and engine power; Alternative size and weight limits, including setting trailer length limits and gross weight limits at values higher or lower than the mid-range values assumed in the preceding section. The average costs used to estimate the productivity benefits of Turner trucks are not adjusted for the effects of downsizing or for the costs of extra safety appurtenances.
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64 NEW TRUCKS FOR GREATER PRODUrnVITY AND LESS ROAD WEAR TABLE 3-6 DIFFERENCE IN OPERATING COSTS PER TON-MILE BETWEEN BASELINE TRUCK AND TURNER PROTOTYPE FOR HIGH-DENSITY TRUCKLOAD FREIGHT Costs per Ton-Mile ($) Difference Baseline Turner Dollars/ Percent Cost Category Trucks Truckb Ton-Mile of Total Driver 0.0154 0.0112 0.0043 62 Interest and depreciation 0.0103 0.0097 0.0006 8 Repairs and maintenance 0.0082 0.0072 0.0010 15 Fuels and fuel taxes 0.0098 0.0083 0.0015 22 Tires and taxes 0.0021 0.0025 -- 0.0005 -- 7 Total 0.0458 0.0389 0.0069 100 NoTE: Costs per ton-mile are from Table 3-4, distributed by cost category according to the FHWA data for the truckload dry van in Table 3-1.
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Use and Productivity 65 First the evidence from the carrier interviews and from the patterns of current use of larger combination trucks is summarized. Then this information is used to estimate the nationwide market for the Turner prototypes and the effect on truck travel of diversion of freight from rail.
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66 NEW TRUCKS FOR GREATER PRODucrIvrrv AND LESS ROAD WEAR However, some typical short-haul applications (e.g., hauling sand and gravel) are also ones in which extra payload weight is most valuable.
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Use and Productivity 67 Loading and Unloading Facilities and Conditions Requirements for and availability of space, labor, and time at loading and unloading points strongly influenced the perceived logistical costs of doubles. Situations in which a queue often forms (construction sites, petroleum terminals)
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68 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LESS ROAD WEAR density freight (Tables 3-4 and 3-5)
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Use and Productivity 69 Reefer Operations using refrigerated trucks (reefers) are diverse.
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70 NEW TRUCKS FOR GREATER PRODucrIvrrY AND LESS ROAD WEAR Factors Influencing Carrier Responses None of the carriers interviewed was unreservedly enthusiastic about Turner trucks, and several stated that they would not use them in applications where, as indicated by the cost analysis in this chapter, they would have an advantage, even after the costs of logistical problems with doubles were considered. In interpreting the responses, several factors influencing how the carriers see the Turner Proposal must be taken into account: Except for a few industry leaders, most for-hire carriers cannot expect increased profits from increased productivity because of the competitive nature of the industry.
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Use and Productivity 71 Almost all carriers interviewed saw potential savings from the greater capacity of the Turner prototypes compared with conventional tractor-semitrailers, but all also recognized added costs per truck-mile of operation and logistical costs associated with using double trailers and introducing new equipment capacities in the transportation system. Most saw the need for detailed analysis of costs and benefits in their operations before an investment decision could be made, although they were able to speculate on how the analysis would come out.
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72 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LEss Ror WEAR tain doubles, and triples -- one or more of which is in use in each of a group of contiguous western states; Eleven-axle semitrailers, doubles, and truck-trailers with weights up to 154,000 lb, used only in Michigan; Heavy truck-trailers with six or more axles used in special applications in some states; Doubles with 28-ft trailers limited to 80,000 lb that are allowed nationwide today; and A large variety of double- and triple-trailer combinations with up to 11 axles and weights up to 140,000 lb used in many parts of Canada. Because several of these combinations are very similar to the Turner prototypes, their use is evidence of the potential scope of the market for the Turner trucks.
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NORTH DAKOTA WISCONSIN SOUTH DAKOTA IOWA NEBRASKA -.- ILLINOIS COLORADO MISSOURI KANSAS S ARIZONA Eastern turnpike doubles system Western LCV region Michigan 11-axle combinations Note: Limited use of larger combinations is allowed in several states not indicated on this map.
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TABLE 3-7 USE OF LONGER AND HEAVIER COMBINATIONS BY REGION, TRAILER BODY, AND RANGE OF OPERATIONS, 1982 (Census Bureau 1985) Double and Triple Combination Miles as Six-or-More-Axle Truck-Trailer Miles as Percent of All Combination VMT in the Percent of All Combination \vIT in the Trailer Range of Cell Cell Body Operations LCV Oreg.- Rest of LCV Oreg.- Rest of Type (mi)
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Use and Productivity 75 through traffic by trucks registered outside the region. The LCV share of through traffic is much less than its share of within-region traffic.)
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76 NEW TRUCKS FOR GREATER PR0DUcrlvrrY AND LESS ROAD WEAR TABLE 3-8 USE OF DOUBLES, TRIPLES, AND TRUCKTRAILERS BY PRINCIPAL PRODUCT, RANGE, AND TRAILER BODY TYPE, 1982 (Census Bureau 1985) Percent of Combination VMT Doubles or Triples Truck-Trailers Product Live animals 1.9 6.0 Farm products 5.5 4.4 Processed food 3.0 1.3 Mining products.
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Use and Productivity 77 surprising either that twins have not been adopted by bulk and other highdensity carriers, because twins are subject to the same 80,000-lb weight limit as semitrailers. It might have been anticipated, however, that twins would be popular among private and for-hire low-density truckload van carriers.
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78 NEW TRUCKS FOR GREATER PRODuCTIvITY AND LESS ROAD WEAR loaded enter into equipment selection decisions. The desirability of being able to use a vehicle configuration to cross the border into the United States probably is one constraint that explains the continued popularity of the five-axle tractor-semitrailer despite Canada's liberal weight laws.
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Use and Productivity 79 The sectors assigned the greatest potential use of the Turner prototypes are intercity dry bulk and LTL carriers. The sectors assigned the least use are for-hire truckload low-density vans, low-density flatbeds, and most local operations.
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80 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR The magnitude of the sectorial shares of larger combinations in the historical data suggests the following quantification of these ratings: low share, 10 percent potential shift of freight to Turner trucks; moderate share, 33 percent; high share, 67 percent. The annual mileage of truck travel that would occur in Turner trucks depends on the current mileage and the mix of vehicles currently employed in each of these sectors.
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Use and Productivity 81 TABLE 3-11 DISTRIBUTION OF CURRENT TRAVEL BY FIVE-OR- MORE-AXLE TRACTOR-SEMITRAILERS, FIVE-AXLE TRUCK- TRAILERS, AND FIVE- AND SIX-AXLE DOUBLES BY MARKET SECTOR, 1987 Billions of Truck Miles Private Carriers For-Hire Carriers Sector Local Intercity Local Intercity Total Van Less than truckload 0 0 0.4 6.3 6.8 Truckload Low density 0.2 2.9 0.2 3.7 7.1 High density 0.6 6.7 0.6 7.1 14.9 Reefer 0.4 3.2 0.2 6.9 10.6 Flatbed Unit loads, automobile haulers, and other low density 0.8 0.9 0.2 2.0 4.0 Other 1.6 2.8 0.6 4.7 9.7 Dry bulk 1.6 2.0 0.9 2.4 7.0 Tanker Petroleum products 0.9 1.3 0.5 1.1 3.8 Nonpetroleum products 0.4 1.1 0.2 1.7 3.4 Total 67.3 SOURCE: Distribution from Census Bureau (1985) (with adjustment for increased use of twin trailer combinations since 1982)
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82 NEW TRUCKS FOR GREATER PRoDucrlvrrY AND LESS ROAD WEAR trailers, which is equivalent to 15 percent of all truck freight projected to be diverted. The seven-axle tractor-semitrailer is assumed to carry highdensity truckload van and flatbed, reefer, bulk, and tanker cargoes only.
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Use and Productivity 83 from rail. If an elasticity of - 1 is assumed, a price decrease averaging 12 cents per truck-mi in existing trucks on 20.2 billion annual truck-mi switching from other trucks to Turner trucks and an average total freight rate of $1.50 per truck-mi in existing trucks would generate new freight for Turner trucks equivalent to 1.8 billion annual existing truck-mi or 1.3 billion additional Turner truck-mi.
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84 NEW TRUCKS FOR GREATER PRoDucrIvnY AND LESS ROAD WEAR TABLE 3-12 DIVERSION OF FREIGHT FROM RAIL TO TURNER TRUCKS BY COMMODITY STCC Code Commodity Annual Truck Ton-Miles Diverted from Rail (billions) Annual Turner TruckMilesb (billions)
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Use and Productivity 85 trucks at the rates shown in Table 3-13. These rates assume that Turner doubles carrying freight shifted from tractor-semitrailers would operate at the less efficient utilization rates shown in Table 3-5 as the penalty for the logistical problems of double-trailer operation, but that the Turner seven-axle tractor-semitrailer and Turner doubles carrying freight shifted from existing twin-trailer combinations would achieve the same capacity utilization as the truck losing the freight.
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TABLE 3-14 TURNER TRUCK FREIGHT DIVERSION AND USE PROJECTIONS Annual Truck-Miles of Freight (billions) Tractor- Semitrailers Truck- and Truck- Trailers Light Turner Trailers Twinsb and LCVs Combinations Total Trucks' Traffic Before Turner Trucks Less than truckload 2.0 4.8 0.1 3.0 9.9 Low-density truckload van and flatbed 10.9 0.2 0.2 5.2 16.5 High-density truckload van and flatbed 34.0 1.2 0.4 8.4 44.0 Tanker and bulk 13.6 0.6 0.3 1.5 16.0 Total 60.5 6.8 1.0 18.0 86.3 Traffic Switching to Turner Double-Trailer Prototypes Less than truckload 0.0 4.3 0.0 0.0 4.3 3.6 Low-density truckload van and flatbed 1.5 0.0 0.0 0.0 1.5 1.2 High-density truckload van and flatbed 6.9 0.3 0.0 0.0 7.2 5.2 Tanker and bulk 3.1 0.2 0.0 0.0 3.4 2.4 Total truck 11.5 4.9 0.0 0.0 16.4 12.5 Rail 1.0
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From page 96... ...
C- Traffic Switching to Turner Single-Trailer Prototype Less than truckload 0.0 0.0 0.0 0.0 0.0 0.0 Low-density truckload van and flatbed 0.0 0.0 0.0 0.0 0.0 0.0 High-density truckload van and flatbed 2.6 0.0 0.0 0.0 2.6 2.2 Tanker and bulk 1.2 0.0 0.0 0.0 1.2 1.0 Total truck 3.8 0.0 0.0 0.0 3.8 3.3 Rail 0.5 Grand total, Turner truck travel 17.3 Five-or-more-axle tractor-semitrailers and five-axle truck-trailers bWjth 28-ft trailers. Six-or-more-axle truck-trailers.
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From page 97... ...
88 NEW TRUCKS FOR GREATER PRoDucrIvrry AND LESS ROAD WEAR larger trucks. These physical problems would probably tend to depress Turner truck use, especially in the East.
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From page 98... ...
Use and Productivity 89 TABLE 3-15 DISTRIBUTION OF RAIL SHIPMENTS OF PRINCIPAL COMMODITIES DIVERTED FROM RAIL TO TURNER TRUCK BY REGION OF ORIGIN Region a Commodityb (billions of total annual ton-mi) Lumber, Pulp, Chem- Coal Wood Food Paper icals Farm Prod- ucts New England - - - 3 - - Middle Atlantic 10 - 1 1 2 - East North Central 11 2 14 3 7 - West North Central 6 1 20 1 4 53 South Atlantic 55 5 4 9 9 1 East South Central 46 4 3 7 5 1 West South Central - 4 5 7 36 6 Mountain 167 7 6 1 15 9 Pacific - 25 16 6 4 8 Nom: Dashes indicate less than 500 million annual ton-mi.
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From page 99... ...
TABLE 3-16 PROJECTED DIVERSIONS FROM EXISTING TO TURNER TRUCKS AND RESULTING FREIGHT COST SAVINGS Savings ($ millions/yr) Savings ($)
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From page 100... ...
Use and Productivity 91 about costs and acceptability of Turner trucks in various applications. Nonetheless, the estimates are a plausible indication of the magnitude of productivity gains that could be achieved with Turner trucks.
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From page 101... ...
4 Safety and 11affic I ncreases in truck size and weight may affect the inherent safety and traffic operations characteristics of combination vehicles as well as the rate of growth of such traffic. The key safety question is what the net systemwide safety impact would be of adopting Turner trucks.
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From page 102... ...
Safety and Traffic 93 Chapter 3 presents estimates of the expected use of Turner trucks and changes in the total travel and operating environment of combination vehicles as the result of adopting Turner trucks. The final objective of this chapter is a synthesis of the estimates of the three foregoing determinants to assess net systemwide changes in number of crashes of combination vehicles due to adopting Turner trucks.
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From page 103... ...
94 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR Examples of research results indicating the influence of the driver on truck accident rates are the following: - Young drivers (under 30) , who make up less than 15 percent of truck drivers, accounted for 30 percent of the drivers of trucks involved in accidents (Eicher et al.
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From page 104... ...
Safety and Traffic 95 safety comparison between Turner trucks and existing trucks, solely because of the differences in physical properties of the two types of trucks when both are operated under identical conditions. These are the factors that would be changed by the new truck size and weight regulations.
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From page 105... ...
96 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR L 4- FIGURE 4-1 Nine-axle Turner double used in demonstration. Traffic Operations Characteristics Traffic operations characteristics of Turner trucks were derived from a review of prior studies.
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From page 106... ...
Safety and Traffic 97 unit of a multiple-unit truck to rapid steering (rearward amplification) , and friction demand in tight turns.
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From page 107... ...
TABLE 4-1 INFLUENCE OF PARAMETER VARIATIONS ON VEHICLE HANDLING AND STABILITY Parameter Variations Gross Target Combination Cargo Trailer Characteristic Value Weight Density Length Tire Suspensions Dollies Brakes Low-speed offtracking 17 ft - - Significant - - Moderate - High-speed offtracking 1 ft Moderate - Significant Significant - Moderate - Braking efficiency 0.7 g Significant Moderate - - - - Moderate Static rollover threshold 0.38 g Significant Significant - - Moderate Moderate - Steering sensitivity 5.7 degrees Moderate Moderate - Significant Moderate Moderate - Rearward amplification 1.4 Significant - Significant Significant - Significant - NoTE: Dashes indicate little or no influence. Significant indicates that the variation has a strong effect on values of the handling and stability characteristics Moderate indicates that the variation has some effect on the handling and stability characteristics.
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From page 108... ...
TABLE 4-2 COMPARISON OF VEHICLE-HANDLING AND STABILITY CHARACTERISTICS BETWEEN PROTOTYPES AND BASELINE TRUCKS Baseline Vehicle Prototype Vehicle Characteristic Polarity of Measure Five-Axle Tractor- Semitrailer' Five-Axle Twin TrailerL Nine-Axle Turnpike Doublec Seven-Axle Tractor- Semitrailer" Nine-Axle B-Train Doubles Nine-Axle DoubIe Eleven-Axle Doubles Low-speed offtracking Lower values (ft) better 15.36 14.27 25.11 15.81 18.87 15.96 13.17 High-speed offtracking Lower values (ft)
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From page 109... ...
100 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LESS ROAD WEAR Kingpin 5th Wheel Offset Tractor Wheelbase Kingpin to Center of Rear Axle or Axles FIGURE 4-2 Tractor wheelbase and kingpin -- rear axle dimension for tractorsemitrailer (TRB 1989)
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From page 110... ...
Safety and Traffic 101 Braking Two major components of truck braking performance are stopping distance capability and vehicle controllability during brake applications. The former, measured by the distance it takes for the truck to come to a complete stop after the brakes have been applied at a given speed, is influenced by a number of factors, including friction available at the tirepavement interface, brake-system characteristics, and distribution of loads on individual axles.
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From page 111... ...
102 NEW TRUCKS FOR GREATER PRODUCrIvITY AND LESS ROAD WEAR rollover threshold increases. Suspension properties and dolly designs also influence static rollover threshold, but are of secondary importance compared with the ratio of width to center-of-gravity height.
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From page 112... ...
Safety and Traffic 103 response to lateral forces, lower gross vehicle weight, and the smallest amount of overhang beyond the wheelbase of the towing unit. Tractor-semitrailers have rearward amplification close to 1.0; that is, the lateral acceleration of the trailer is nearly the same as that of the tractor during steering maneuvers.
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From page 113... ...
104 NEW TRUCKS FOR GREATER PRoDucrivin' AND LESS ROAD WEAR (and thus longer effective trailer wheelbase) reduce rearward amplification and decrease high-speed offtracking, but increase low-speed offtracking.
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From page 114... ...
Safety and Traffic 105 these trailer length limits would be similar to the baseline five-axle 45-ft tractor-semitrailer. Exceptions are the 38-ft 11-axle double, the B-train double, and the 50-ft tractor-semitrailer, which would have low-speed offtracking similar to that of existing 5-axle 48-ft tractor-semitrailers.
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From page 115... ...
106 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR make, and more important, weight savings that would allow larger payloads to be carried. In the interviews, suppliers and carriers indicated two reasons why the extent of component downsizing probably would be quite limited, especially in the early years of use of Turner trucks.
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From page 116... ...
Safety and Traffic 107 . Wide-base single tires with high cornering stiffness (1,150 lb per degree or more)
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From page 117... ...
108 NEW TRUCKS FOR GREATER PRoDucrIvrn' AND LESS ROAD WEAR DUALS RETROFIT WIDE-BASE SINGLES I I I I ORIGINAL EQUIPMENT :0 WIDE-BASE SINGLES FIGURE 4-4 Influenëe of wide-base single tire on the overall width to the outside of the tires on an axle (Fancher et al.
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From page 118... ...
Safety and Traffic 109 Coupling Systems Relative to single-drawbar dollies, which create two points of articulation between the two trailers of a double trailer combination and are commonly used on doubles in the United States, the use of the B-train configuration or the double-drawbar dolly (Figure 2-1) , which allows only one articulation, would reduce rearward amplification and high-speed offtracking of all prototype doubles.
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From page 119... ...
110 NEW TRUCKS FOR GREATER PRonucriviTY AND LESS ROAD WEAR two-lane highways, common freeway maneuvers (such as merging, weaving, lane changing, and exiting) , intersection operations, downhill operations, splash and spray, aerodynamic buffeting, blockage of view, truck blind spots, backing up for loading and unloading, and longitudinal barriers for restraining and redirecting vehicles upon impact.
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From page 120... ...
Safety and Traffic 111 TABLE 4-4 continued Characteristic Comparison Between Turner Trucks and Trucks Replaced Intersection sight dis- Prototype Turner doubles would increase sight tance required for distance required by up to 10 percent relative trucks to cross unsig- to existing 28-ft twins. nalized intersections Intersection sight dis- Prototype Turner trucks, if operated by the exist- tance required for ing range of engine power, would increase sight turning at unsignalized distance required because of their lower accel- intersections eration capability.
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From page 121... ...
112 NEW TRUCKS FOR GREATER PRoDucriviTy AND LESS ROAD WEAR Walton 1986; Strawhorn and Suski 1985) , and the highest horsepower currently available in the United States, which is used with turnpike doubles (tractors pulling two 45-ft trailers)
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From page 122... ...
Safety and Traffic 113 loads and lighter non-Turner loads might choose an engine size that is a compromise. A Turner double capable of maintaining 20 mph on a 5 to 6 percent upgrade would perform quite comparably to most existing tractor-semitrailers (Table 4-5)
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From page 123... ...
114 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LEss ROAD WEAR than that of existing tractor-semitrailers. In severe weather, the use of these Turner doubles would likely be restricted by their traction ability.
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From page 124... ...
Safety and Traffic 115 longer passing sight distance requirements for Turner doubles than for existing tractor-semitrailers or five-axle twin trailers. In practice, such passing maneuvers would likely not be practical except under the most ideal conditions.
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From page 125... ...
116 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LESS ROAD WEAR and deceleration characteristics of the two types of truck are not expected to be significantly different. Intersection Operations Turns at Unsignalized Intersections If a Turner truck had a lower ratio of power to weight than existing trucks, then when turning onto a major road from a stopped position on a minor road at an unsignalized intersection it would require more time to attain the travel speed on the major road after completing the turn.
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From page 126... ...
Safety and Traffic 117 Failure of drivers to properly downshift while descending steep hills can lead to brake overheating or total brake failure. Brake torque and thermal capacity, brake conditions, and GVW relative to maximum rated vehicle weight affect the probability of brake overheating (Fancher and O'Day 1981)
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From page 127... ...
118 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR Aerodynamic Buffeting The likelihood of potentially hazardous aerodynamic buffeting as cars approach and pass trucks increases as the size of the trucks increases. Further, trucks are more susceptible to being buffeted by strong crosswinds as their surface area increases (FHWA 1986)
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From page 128... ...
Safety and Traffic 119 doubles would likely require more yard space for maneuvering. However, the increased trailer length is not so great as to make the loading and unloading significantly more difficult.
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From page 129... ...
120 NEW TRUCKS FOR GREATER PRoDuclivrrY AND LESS ROAD WEAR model of the relationship between handling and accident rate -- an assessment was made of the orders of magnitude of accident rate differences between the Turner prototypes and the trucks they would replace, operated under identical conditions. Accident Rates of Existing Doubles and Tractor-Semitrailers In the TRB study of twin trailer trucks (1986)
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From page 130... ...
Safety and Traffic 121 one exception, their findings are consistent with the conclusion of the 1986 TRB study. The exception is reported by Stein and Jones (1988)
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From page 131... ...
122 NEW TRUCKS FOR GREATER PRoDUcrIvn-y AND LESS ROAD WEAR Fatal accident rates per mile traveled by accident type corresponding to individual handling and stability characteristics were estimated from the University of Michigan Transportation Research Institute data bases Trucks Involved in Fatal Accidents (TIFA) and National Truck Trip Information Survey (NTFIS)
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From page 132... ...
Safety and Traffic 123 01 I I I I 0.3 0.4 0.5 0.6 0.7 Rollover Threshold, g FIGURE 4-5 Rollover threshold versus fatal involvement rate (Fancher et al.
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From page 133... ...
30 01 I 1 I I I 1 I I I 0.8 1.0 1.2 1.4 1.6 1.8 2.0 124 NEW TRUCKS FOR GREATER PRoDucrIvliY AND LESS ROAD WEAR rates increase as steering sensitivity decreases below 9.0 degrees/g (Figure 4-8)
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From page 134... ...
Safety and Traffic 125 Similar relationships for total accidents (fatal plus nonfatal) could not be developed at this time, because data on nonfatal truck accidents are incomplete and lack necessary detail.
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From page 135... ...
126 NEW TRUCKS FOR GREATER PRoDucrlvrry AND LESS ROAD WEAR involvement rate is about 3 percent lower than that of the baseline fiveaxle twins. The prototype seven-axle tractor-semitrailer, with 48-ft trailer and a maximum GVW of 91,000 ib, is predicted to have a 2 percent lower fatal involvement rate than that of the baseline tractor-semitrailer.
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From page 136... ...
Safety and Traffic 127 acteristics were obtained from the TIFA data and the NITIS travel data, which are based on different time periods. That is, the TIFA data are available for 1980 through 1984, whereas the NTTIS travel data are available only for 1985.
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From page 137... ...
128 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR should be noted that the presence of many of the traffic interaction effects characteristic of Turner trucks would be correlated in the existing fleet with the presence of handling and stability properties similar to those of Turner trucks. For example, a truck with worse-than-average offtracking would also be likely to be longer than average (a feature of some Turner trucks that has adverse traffic interaction effects)
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From page 138... ...
Safety and Traffic 129 bilities of fatality and injury than those on urban highways. Therefore truck configuration has only a small effect on accident severity (TRB 1986)
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From page 139... ...
130 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR On a systemwide basis, if Turner trucks were adopted, the annual number of fatal combination truck accident involvements would decrease by 2.6 percent. This estimate is based on the estimated relative fatal involvement rates per mile of travel (Table 4-6)
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From page 140... ...
Safety and Traffic 131 Vehicle Parameters To Reduce Rearward Amplification Rearward amplification contributes to a higher number of rollover accidents of doubles relative to tractor-semitrailers. A minimum trailerwheelbase dimension and a maximum hitch offset would ensure that Turner doubles would not have excessive rearward amplification (Figure 4-3)
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From page 141... ...
132 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR tion vehicles. A minimum-speed performance standard on grades would minimize accident risk due to excessive speed reductions in mountain driving.
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From page 142... ...
Safety and Traffic 133 rearward amplification, which is not experienced by tractor-semitrailers, these Turner doubles would also have slightly better overall handling and stability properties than existing tractor-semitrailers. These findings hold if similar tires, suspensions, and brakes are used both on Turner doubles and on existing trucks.
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From page 143... ...
134 NEW TRUCKS FOR GREATER PRoDucTIvITY AND LESS ROAD WEAR number of truck accidents could be reduced by 2.6 percent. The reduction in miles of travel of combination vehicles would also produce a positive impact that could help to balance the negative traffic operations characteristics of Turner trucks relative to the existing combination vehicles they would replace.
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From page 144... ...
Safety and Traffic 135 Gillespie, T
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From page 145... ...
5 Bridges The effects of large trucks on bridges, the methods used in this study to estimate bridge-related costs of introducing Turner trucks, and the results of the cost estimates are described in this chapter. EFFECTS OF TRUCKS ON BRIDGES Two types of bridge response must be considered in evaluating the effect of changes in truck size: overstress and fatigue.
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From page 146... ...
Bridges137 building stronger bridges, closing deficient bridges to Turner trucks, or, conceivably, changing their practices and criteria. Overstress The bending moment caused by a truck on a bridge induces stress in the elements of the bridge.
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From page 147... ...
138 NEW TRUCKS FOR GREATER PRoDucrivifY AND LESS ROAD WEAR consequences of a load that exceeds the strength of a member depend on the importance of that member to the performance of the entire structure. Some member failures may cause a total collapse of the structure, whereas failure of other members may cause only slight distortion and load redistribution.
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From page 148... ...
Bridges 139 The distinction between inventory and operating ratings is important, because the criterion applied determines whether a bridge would be judged adequate to withstand the increased loading when weight regulations are changed to allow larger trucks. Of the 46 states responding to the survey of state bridge engineers conducted for this study (Moses 1989)
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From page 149... ...
140 NEW TRUCKS FOR GREATER PRoDucrIvin' AND LESS ROAD WEAR Overstress of Existing Bridges The cost of overstress for existing bridges was estimated by Specifying legal loadings for existing trucks and the prototypes that represent worst cases for bridge impacts (Figure 5-1) , Compiling information on the load-bearing capacities of existing bridges from the National Bridge Inventory maintained by the FHWA, Identifying load-deficient bridges with existing traffic and with traffic including the Turner prototype trucks, Calculating the cost to replace those bridges that are deficient for carrying traffic with Turner prototypes but adequate for existing traffic, and Estimating the percentage of bridges that it would be necessary to replace or to post, by road class, in order to create a system sufficiently extensive to carry most types of traffic expected in Turner trucks.
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From page 150... ...
TURNER PROTOTYPE TRUCKS SEVEN-AXLE TRACTOR-SEMITRAILER: WB = 54.0 ft, GVW = 91,000 lb LOL6cDU 4 __ ______ 7.7 4.3 4.3 29.1 4.3 4.3 ft 11 13.33 13.33 13.33 13.33 13.33 13.33 klb NINE-AXLE DOUBLE: WB = 774 ft, GVW = 111,000 lb u.0 4.i 4.3 21.5 4.3 ft 11 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 klb NINE-AXLE B-TRAIN DOUBLE: WB = 78.9 ft, GVW = 111,000 lb 9.85 4.3 23.9 4.3 4.3 4.3 23.65 4.3 ft 11 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 klb ELEVEN-AXLE DOUBLE: WB = 77.5 ft, GVW = 141,000 lb 9.85 4.3 14.75 4.3 4.3 10.85 4.3 16.25 4.3 4.3 ft 11 12.5 12.5 13.3313.3313.33 12.5 12.5 13.33 13.33 13.33 klb FIGURE 5-1 Axle loadings and spacings for prototypes and existing trucks (WB = maximum wheelbase; GVW = maximum gross vehicle weight)
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From page 151... ...
Sensitivity Analysis on Length NINE-AXLE DOUBLE PLUS 15 PERCENT IN LENGTH:WB = 89.05 It, GVW = 111,000 lb 9.85 4.3 24.6 4.3 10.9 4.3 26.5 4.3 ft 11 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 klb NINE-AXLE DOUBLE MINUS 15 PERCENT IN LENGTH:WB = 65.75 ft, GVW = 111,000 lb I 4 '-k+ ) j4.( 9.85 4.3 15.4 4.3 6.8 4.3 16.5 4.3 ft 11 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 klb Sensitivity Analysis on Weight NINE-AXLE DOUBLE PLUS 15 PERCENT IN WEIGHT:WB = 774 ft, GVW = 127,800 lb I If 'I'I' i"I-' 9.85 4.3 20.0 4.3 8.85 4.3 21.5 4.3 ft 12.6 14.4 14.4 14.4 14.4 14.4 14.4 14.4 14.4 klb NINE-AXLE DOUBLE MINUS 15 PERCENT IN WEIGHT: WB = 77.4 ft, GVW = 94,200 lb I -k 10 k -I 40 k 0-II 9.85 4.3 20.0 4.3 8.85 4.3 21.5 4.3 ft 9.4 10.6 10.6 10.6 10.6 10.610.6 10.6 1 10.6 klb FIGURE 5-1 continued
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From page 152... ...
Sensitivity Analysis on Length and Weight NINE-AXLE DOUBLE PLUS 15 PERCENT IN LENGTH AND WEIGHT: WB = 89.05 ft, GVW = 127,800 lb 445 9.85 4.3 24.6 4.3 10.9 4.3 26.5 4.3 ft 12.6 14.4 14.4 14.4 14.4 14.4 14.4 14414.4 klb EXISTING TRUCKS: AASHTO TYPICAL LEGAL LOAD TYPES (AASHTO 1979)
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From page 153... ...
144 NEW TRUCKS FOR GREATER PRoDuclivrrY AND LESS ROAD WEAR options: (a) replace the bridge, (b)
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From page 154... ...
Bridges 145 permitted by AASHTO.) The tolerance was applied to reflect the practice of many agencies that do not post for loads within 5 percent of legal weight.
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From page 155... ...
146 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR moment of the standard truck. The bending moment depends on the axle weights and axle spacings of the truck and the length of the bridge span.
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From page 156... ...
Bridges 147 In 1987 the states spent $3 billion for new bridges, bridge replacement, and bridge rehabilitation (FHWA 1988)
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From page 157... ...
148 NEW TRUCKS FOR GREATER PRODuCrIvITY AND LESS ROAD WEAR TABLE 5-1 BRIDGE FATIGUE IMPACTS OF TURNER TRUCKS Existing Truck Traffic Switching to Turner Trucks Traffic Diversion (truck-mi billions) Percent Change in Rate of Fatigue Damage Per Billion Annual Total Truck-Mi Diverted Five-axle tractor-semi- trailer to nine-axle Turner double 11.5 12.0 1.0 Five-axle tractor-semi- trailer to seven-axle Turner tractor-semi- trailer 3.8 0.7 0.2 Five-axle twin to nine-axle Turner double ...4.2 3.3 0.7 Total 20.2 16.0 0.8 Rail to Turner truck -" 2.2 Total with rail diversion 18.2 Freight diverted from rail is projected to add 1.5 billion annual mi of travel by Turner trucks.
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From page 158... ...
Bridges 149 from a 77-ft wheelbase) would reduce the added fatigue cost by 50 percent if all trucks took advantage of the additional legal length, and by proportionately less if some trucks operated at shorter lengths regardless of the maximum allowed.
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From page 159... ...
150 NEW TRUCKS FOR GREATER PRODuCTIvITy AND LESS ROAD WEAR For traffic including the two prototype trucks likely to be most widely used, the nine-axle double and the seven-axle tractor-semitrailer, 7,000 Interstate and primary bridges (5 percent of the total) would fail the overstress criterion over and above those that do not meet the criterion today (Table 5-2)
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From page 160... ...
Bridges 151 criterion over and above the base case. These would cost $9.4 billion to replace.
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From page 161... ...
152 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR have had long remaining lifetimes if Turner trucks had not been introduced. If any appreciable number of these bridges were likely to be replaced soon (say, within 5 years)
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From page 162... ...
Bridges 153 be extensive enough in some areas that the potential use of Turner trucks would be substantially curtailed. The states' responses to the bridge capacity demands of Turner trucks would have to be managed so that the proposal in practice did not lose its key element, which is to represent a "win-win" arrangement, one seen as beneficial by both truck operators and highway agencies.
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From page 163... ...
154 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR of all Interstate and primary bridges are located. Sixteen percent of all Interstate and primary bridges in these six states are adequate for existing traffic but would be deficient to carry Turner prototypes.
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From page 164... ...
Bridges 155 deficiencies attributed to the Turner nine-axle double and seven-axle single prototypes would occur in six states (not the same six as for Interstate and primary deficiencies)
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From page 165... ...
156 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR This computation assumes a 7 percent rate of interest and infinite term for amortizing capital costs. That is, the $193 million annualized cost of replacement for all deficient Interstate and primary bridges is 7 percent of the total cost for replacing these bridges (reported as $2.76 billion in the section on overstress costs above)
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From page 166... ...
Pavements Reducing pavement wear, and thus improving the average condi-tion of roads and saving pavement maintenance and construction costs, was one of the principal benefits that motivated the Turner Proposal. As described in Chapter 2, highway agencies are spending several billion dollars annually to repair and reconstruct pavements, and car and truck operating costs per mile can easily be as much as 25 percent higher on deteriorated pavement than on pavement in good condition.
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From page 167... ...
158 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR Turner weight limits and assumptions about the kinds of tires used and about highway agency pavement design practices. PAVEMENT WEAR MODEL All road pavements deteriorate over time through the formation of cracks, rutting in wheel paths, roughening of the surface, and other mechanisms.
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From page 168... ...
Pavements 159 ing useful life of the pavement, as the passage of 1.09 standard 18,000-lb single axles. The equivalency relationships were calibrated from the Road Test.
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From page 169... ...
160 NEW TRUCKS FOR GREATER PRoDUcrIvrrY AND LESS ROAD WEAR reasons. The trucking industry has held that it is invalid for predicting the effect of changes in truck weight on damage of pavements in use, because of the accelerated testing methods used and because it does not properly reflect the role of weather in causing damage (American Trucking Associations 1983)
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From page 170... ...
Pavements 161 The change in the cost of maintaining pavements resulting from the change in the rate of wear was estimated under the assumption that highway agencies would act to keep pavement condition and intervals between resurfacing the same as they would have been if traffic had not changed. Sensitivity analyses were used to examine how cost estimates would change if several assumptions were changed: use of single tires in place of duals by a portion of the Turner trucks, various axle weight limits for Turner trucks, changes in suspension design, and a new policy by highway agencies of constructing heavier, more durable pavements than is current practice.
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From page 171... ...
162 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR weight data. The weight distributions for the diverted traffic were the FHWA distributions adjusted to match the averages from the carrier interviews.
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From page 172... ...
Pavements 163 Results Pavement Wear Effect of Traffic Shifts The results of the computation of changes in rate of ESAL accumulation are summarized first in terms of impact per unit of truck traffic shifted to Turner trucks from other vehicles (Table 6-1) and then in the aggregate for the total volume of traffic projected for Turner trucks.
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From page 173... ...
TABLE 6-1 PAVEMENT WEAR EFFECTS OF DIVERSION OF FREIGHT FROM EXISTING TRUCKS TO TURNER PROTOTYPES Trucks Losing Freight Trucks Gaining Freight ESAL-Mi ESAL-Mi Net De- per Annual ESAL- per crease in Annual Avg Gross Avg ESAL- Thousand Mi Avg Gross Avg Mi Thousand ESAL- Effects of 1 Billion Annual Mi Lost Weight (lb ESALs Mi Lost Payload Gained Weight (lb ESALs Gained Payload Mi (bil- Mi of Traffic Diverted (billions) thousands)
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From page 174... ...
Pavements 165 result of the Turner truck's 45 percent fewer ESALs per truck and the 27 percent fewer truck-miles it would require to carry the freight. In absolute terms, for each mile of five-axle tractor-semitrailer travel that is replaced by a Turner nine-axle double, a net saving of 0.8 ESAL-mi would be achieved (Table 6-1)
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From page 175... ...
TABLE 6-2 AGGREGATE CHANGE IN ANNUAL ESAL-MILES RESULTING FROM USE OF TURNER TRUCKS Annual Truck-Mi et Decrease in N ESAL-Mi per Decrease in Annual in Existing Truck-Mi Switching ESAL-Mi (billions) Vehicle Switching to Turner to Turner Traffic Diversion (billions)
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From page 176... ...
Pavements 167 truck traffic diverted (Table 6-1) , the projected total decrease from freight switching to Turner trucks is 20.6 billion ESAL-milyear (Table 6-2)
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From page 177... ...
168 NEW TRUCKS FOR GREATER PRODUCr! VITY AND LESS ROAD WEAR same lifetime for all pavements regardless of traffic volume.
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From page 178... ...
Pavements 169 pavement cost simulation indicates that the annual cost increase from a 10 percent increase in ESALs on all roads would be $370 million annually. Of this, 93 percent would be for preserving existing roads and 7 percent for the average annual increase in the cost of building new roads because of higher expected traffic loadings.
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From page 179... ...
170 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR Chapter 2 that returns to additional expenditures for road rehabilitation would be very high implies that these user cost savings would likely be greater than the highway agency savings if spending for pavements were reduced. The highway agency cost changes estimated in the preceding section include only changes in capital expenditures.
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From page 180... ...
Pavements 171 and because many of the logistical problems of using double trailers, which are related to lack of space, older facilities, and congestion, are severe in the region. In certain states that already allow relatively unrestricted use of longer and heavier trucks than those used nationwide, including several western states and Michigan, Turner trucks would have less appeal to local operators than existing trucks.
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From page 181... ...
172 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR Turner trucks would have lighter axle loads than current trucks, carriers would find it easier to substitute singles for duals. Single tires very similar to the tires in general use today can support Turner axle loads.
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From page 182... ...
Pavements 173 The first three of these issues are analyzed in more detail in the following sections. Conclusions regarding pavement impacts of tires and suspensions rely on a literature review of research in these areas (Deacon 1988b)
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From page 183... ...
174 NEW TRUCKS FOR GREATER PRoDUcTivITY AND LESS ROAD WEAR highway. Unbalanced loads between the tires of a dual set can occur as a result of unequal tire pressures, uneven tire wear, and pavement crown.
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From page 184... ...
Pavements 175 If all of the projected traffic in Turner trucks were equipped with single tires rather than duals on all wheels, and the effect of this were to increase the ESAL rating of every Turner truck by 77 percent, as the analysis described above suggests, the average net decrease in ESAL-miles per truck-mile switching to Turner vehicles on asphalt pavement (Table 6-2) would decline from 0.97 (predicted assuming dual tires)
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From page 185... ...
176 NEW TRUCKS FOR GREATER PRODUCr! vrry AND LESS ROAD WEAR fore, even without restrictions on their use, it is unlikely that more than a minority of Turner trucks would be equipped with single tires.
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From page 186... ...
Pavements 177 Steerable axles can reduce pavement wear by reducing sideways forces during turning, but the major significance of their use is their effect on maneuverability. The B-train with nonsteering axles in all positions under the trailers would have to be restricted to a shorter length than the other Turner double-trailer prototypes if it were to maintain comparable lowspeed offtracking.
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From page 187... ...
178 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR the pavement impact computations were repeated with heavier tractor tandem axles on fully loaded Turner nine-axle doubles carrying truckload freight diverted from other trucks and from rail. The quantity of freight carried by Turner trucks was assumed to be unaffected.
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From page 188... ...
rA Conclusions and Recommendations The examination of the potential consequences of using Turner trucks has shown that their nationwide use, replacing existing trucks in applications where they would lower the carrier's freight transport cost, would reduce the rate of deterioration of highway pavement. Costs to maintain and construct bridges would increase, but by an amount less than pavement savings if Turner trucks are prevented from using some secondary road bridges now open to large trucks on routes lightly traveled by large trucks.
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From page 189... ...
180 NEW TRUCKS FOR GREATER PRoDucrivin' AND LEss ROAD WEAR The volume of freight and truck travel that would be handled with Turner trucks and the effect of this travel on freight costs, Safety and traffic flow, Bridges, and Pavement condition and cost. The important impacts in each category are given in Table 7-1.
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From page 190... ...
TABLE 7-1 continued Category Impact Safety and Traffic Flow Traffic interaction Passing more difficult because of length of dou- bles; merging, lane changing, and exiting diffi- cult because of double's length; may degrade traffic operations in urban congestion Accident rates and Se- No different from existing tractor-semitrailers un- verity der similar conditions, provided recommended equipment and driver requirements employed Systemwide safety No overall increase in highway accident losses; projected decline in truck travel a potential safety gain Bridges Structural deficiencies 7,000 Interstate and other primary bridges and 19,000 nonprimary bridges (currently ade- quate) ; number could be reduced by careful screening to base restrictions on actual capacity Replacement costs $2.8 billion one-time cost to replace all inade- quate Interstate and other primary bridges ($400,000 per bridge)
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From page 191... ...
182 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR Use and Productivity The analysis of the Turner Proposal was organized around a set of prototype trucks: a 7-axle tractor-semitrailer, a 9-axle double with two equallength semitrailers coupled by a single-drawbar or double-drawbar dolly; an 11-axle double, and a 9-axle B-train double, which has two semitrailers coupled by a fifth wheel affixed at the rear of the first semitrailer, rather than by a dolly. Many other vehicles that conform to the Turner concept are possible, and truck operators usually respond to a change in size and weight regulations by devising a variety of vehicle modifications to suit specific needs.
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From page 192... ...
Conclusions and Recommendations 183 Lower utilization rate for equipment and drivers: more time may be required for pickup and delivery in a double-trailer combination, and equipment is used less efficiently when a fleet operation must dispatch several different sizes of trailers and tractors, effectively dividing each traffic lane into several lower-traffic-density, less efficient lanes. Requirements for modification of facilities at loading and unloading points, for example, acquiring more yard space for maneuvering and storing trailers or increasing the number of loading bays.
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From page 193... ...
184 NEW TRUCKS FOR GREATER PRooucrnvrrY AND LEss ROAD WEAR nc incompatibility would restrict their use on a few percent of rural Interstate miles and a significant fraction of other rural primary miles. Productivity Gains Savings to carriers adopting Turner trucks would average 12 percent of line-haul operating costs.
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From page 194... ...
Conclusions and Recommendations 185 both configurations are equipped with similar tires. Using single tires or smaller dual tires on the trailers and dolly of Turner doubles would negate this advantage.
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From page 195... ...
186 NEW TRUCKS FOR GREATER PRoDucriviTy AND LESS ROAD WEAR The need to keep low-speed offtracking within the limits of the available roadway space would effectively restrict the overall length of Turner trucks operated on non-Interstate roads. Operations of Turner trucks substantially longer than existing combination vehicles would likely degrade traffic operations or safety in extreme urban congestion because of difficulty in merging, lane-changing, and exiting maneuvers.
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From page 196... ...
Conclusions and Recommendations 187 Nonetheless, Turner doubles are not expected to have higher rates of rollover crashes per mile traveled than existing doubles. If no special measures were taken to improve their safety, the Turner doubles would probably have an accident rate slightly worse than that of the five-axle tractor-semitrailer they would replace and equal to or slightly better than that of the five-axle twin trailers replaced, when operated under identical conditions.
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From page 197... ...
188 NEW TRUCKS FOR GREATER PRoDUcrIvrrY AND LESS ROAD WEAR Sumption in the analysis was that highway agencies would continue to follow current practice regarding design standards for new bridges and criteria for posting existing bridges to restrict truck traffic. The criterion in the analysis to determine whether existing bridges must be posted or replaced was that loads should not exceed a bridge's operating rating, a rating of the maximum safe load for a bridge determined according to a method defined by AASHTO and which for steel bridges nominally equals 75 percent of the yield load.
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From page 198... ...
Conclusions and Recommendations 189 The largest prototype truck considered in the study, the 11-axle double, would be impractical as a truck for general, nationwide use because of high bridge costs. Potential bridge costs would likely be comparable with or exceed pavement wear savings in some jurisdictions.
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From page 199... ...
190 NEW TRUCKS FOR GREATER PRoDuclivify AND LESS ROAD WEAR as they would have been if traffic had not changed. The cost would be altered in two respects: the time to the next resurfacing of a pavement and the thickness of subsequent resurfacings.
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From page 200... ...
Conclusions and Recommendations 191 the fee. With any fee required for continued use of existing trucks, Turner truck use would be higher than with no fee.
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From page 201... ...
192 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR suggested would be sufficient to ensure that Turner trucks could use nearly all roads significant for truck traffic, that is, if all additional Interstate and primary and one-fourth of all nonprimary bridges deficient for Turner trucks but adequate for existing trucks were replaced. Then, after Turner trucks had achieved their ultimate level of market penetration, highway agencies annually would experience a $729 million reduction in pavement costs and a $403 million increase in bridge costs, for an eventual net saving of $326 million a year in the cost to maintain highways in the condition that would prevail if Turner trucks were not used.
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From page 202... ...
TABLE 7-2 ILLUSTRATIVE ANNUAL COST CHANGES AND PRESENT VALUES Cost ($ millions) by Year 7 and 0 1 2 3 4 5 6 Following Case 1: All Bridge Replacement in First Year; Use Grows over 7 Years Bridge replacement 3,782 New bridges 110 110 110 110 110 110 110 110 Bridge fatigue 0 4 8 12 16 20 24 28 Pavement wear 0 -- 104 -- 208 -- 312 -- 417 -- 521 -- 625 -- 729 Net highway agency cost 3,892 10 -- 90 1190 -- 291 -- 391 -- 491 -- 591 Net present value at 7 percent -- 2,786 Case 2: Bridge Replacement Staged over 4 Years Bridge replacement 946 946 946 945 New bridges 110 110 110 110 110 110 110 110 Bridge fatigue 0 4 8 12 16 20 24 28 Pavement wear 0 -- 104 -- 208 -- 312 -- 417 -- 521 -- 625 -- 729 Net highway agency cost 1,056 956 855 755 -- 291 -- 391 -- 491 -- 591 Net present value at 7 percent -- 3,141 Case 3: Outlays as in Case 2 but Differing Discount Rate Net present value at 3 percent - 14,024 Net present value at 12 percent -- 22 Case 4: Bridge Replacement Staged over 4 Years; Turner Truck Use One-Half That Predicted Net highway agency cost 1,056 1,006 955 905 -- 91 -- 140 -- 191 -- 240 Net present value at 7 percent 989
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From page 203... ...
194 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR replacements that is assumed in the bridge cost estimate, then bridge costs would remain nearly unchanged but pavement savings would fall by approximately the full 50 percent and the net impact on highway agencies would be changed from $326 million annual savings (after full adoption of Turner trucks) to $25 million annual increase in costs (Table 7-3)
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From page 204... ...
Conclusions and Recommendations 195 OVERALL EVALUATION The availability on U.S. roads of Turner trucks operating according to the procedures recommended by this study would produce benefits from savings in the cost of shipping freight and savings in the cost of maintaining and preserving the road system.
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From page 205... ...
196 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR would derive a savings from Turner trucks, the likely need for substantial investment for bridge improvements initially, before Turner trucks could be used, would expose the state to the risk that expected Turner traffic may not materialize or that it may be delayed for so long that the present worth of the pavement benefits would be greatly diminished. A state that expected a net increase in highway costs might nonetheless reasonably decide to adopt the proposal to aid economic development.
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From page 206... ...
Conclusions and Recommendations 197 Whether the Turner Proposal is adopted nationwide or in only some states, a national program perspective and coordination are essential. The following recommendations for Turner trucks should be implemented as a package if the Turner Proposal is to be successful in producing its intended benefits.
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From page 207... ...
TABLE 7-4 RECOMMENDED TURNER VEHICLE RESTRICTIONS Parameter Restriction Weight (ib) , maximum Single axle 15,000 Tandem axle 25,000 Tandem drive axle 28,000 Triaxle 40,000 Four-axle group 50,000 Gross combination - Bridge formulab 500[LN/(N-1)
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From page 208... ...
Conclusions and Recommendations 199 Weight Recommendations Maximum permissible gross weights for axles should be as follows: Single axle, 15,000 lb; Tandem axle, 25,000 lb; Tandem tractor drive axle, 28,000 lb; Triaxie, 40,000 lb; and Four-axle group, 50,000 lb. Weight should be further limited by the following formula: 500 [LN/(N - 1)
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From page 209... ...
200 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR increase in highway costs, contrary to the objective of the proposal. A sensitivity analysis indicates the magnitude of these trade-offs.
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From page 210... ...
Conclusions and Recommendations 201 Double trailers, 34 ft maximum and 32 ft minimum for each trailer other than in B-trains; B-train, 67 ft maximum box length (from front of first trailer to rear of second) and 28 ft minimum trailer length; and Axle spacings, 69 ft minimum on any group of nine axles, from center to center of extreme axles, 59 ft minimum on group of eight axles, and 49 ft minimum on group of seven axles.
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From page 211... ...
202 NEW TRUCKS FOR GREATER PR0DUcrlvrrY AND LESS ROAD WEAR also offers productivity advantages to carriers of low-density as well as high-density freight. The trailer length limits are compatible with the two most common container lengths in use today, 20 ft and 40 ft.
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From page 212... ...
Conclusions and Recommendations 203 turer's designated nominal tire section width. The effect of this requirement is that if single tires were used, they would have greater width and about the same inflation pressure as the tires most commonly used on combination trucks today.
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From page 213... ...
204 NEW TRUCKS FOR GREATER PR0DuCTIvIFY AND LESS ROAD WEAR trucks to be within the range of performance commonly encountered in large trucks in use today. Second, the required engine Size would be economically feasible to operate and would be within the range of engine sizes for road tractors now in standard production.
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From page 214... ...
Conclusions and Recommendations 205 posal infeasible. If the effect of requiring a particular safety feature (for example, antilock brakes on trailers of Turner trucks)
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From page 215... ...
206 NEW TRUCKS FOR GREATER PRoDucriviTY AND LESS ROAD WEAR training program in the Turner truck type being operated. Each state where Turner trucks are allowed should provide for certification of these requirements, either through an endorsement on Turner operators' commercial driver's licenses or through provision of special permits for carriers using Turner trucks.
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From page 216... ...
Conclusions and Recommendations 207 Deficient Bridges The inaccessibility of certain routes and locations because of bridges that are inadequate to carry Turner trucks would be the major initial impediment to gaining the benefits of Turner trucks. Therefore, each state should develop a long-range plan for alleviating constraints on the use of Turner trucks because of deficient bridges.
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From page 217... ...
208 NEW TRUCKS FOR GREATER PRODuCrIvITY AND LESS ROAD WEAR would be the need for immediate spending to remove bridge deficiencies on important truck routes. In setting priorities for spending available funds for bridge work, highway agencies should recognize the possible pavement benefits over time of expenditures that facilitate use of Turner trucks.
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From page 218... ...
Conclusions and Recommendations 209 Adopt the size, weight, configuration, and equipment restrictions recommended in this report, together with the procedures for dealing with deficient bridges and special routing problems specified below (i.e., Turner truck regulations) , as an AASHTO policy guide to the states.
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From page 219... ...
210 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR neighboring states on bridge postings, priorities for removing bridge deficiencies, limits, and enforcement. Enforcement and Monitoring Turner Truck Registration The states should require declaration of the intent to operate a Turner truck at the registration of the tractor and trailers or at the application for a special permit.
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From page 220... ...
Conclusions and Recommendations 211 with the proper incentives to choose trucks that are truly the most efficient, considering both highway and truck operating costs. These adjustments would be particularly important for the implementation of the Turner Proposal because state tax systems are not designed to adjust to a Turner truck that occasioned lower highway costs than a conventional tractor-semitrailer.
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From page 221... ...
212 NEW TRUCKS FOR GREATER PRODUcTIvrrY AND LESS ROAD WEAR Serious practical obstacles exist to applying such an ideal approach. Nevertheless, greater pressures for efficient highway management and freight transport, together with advances in automated highway monitoring and communications, eventually could lead to greater reliance on taxes and fees to regulate truck size and weight.
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From page 222... ...
APPENDIX A Looking Ahead from Milepost 1984 at the f'ederal-Aid Highway Program' francis C Turner My instructions for this session are "to identify what I believe to be the top current issues in highways which the states ought to be concerned about, and to make suggestions as to actions by you thereon." It is easy to draw up a list of 300 issues, but to limit it to only a handful is much more difficult, however my selections are as follows: Persuade our Congressional partners to look at and act on needed highway legislation as national statesmen, Phase down our Interstate system program to early completion, and transfer the same degree of emphasis to the other systems, Enact additional highway user revenues and extend the Highway Trust Fund without a terminal date, Redesign heavy highway trucking units to substantially reduce the damage factor and thus extend pavement and bridge life, Take actions to drastically reduce highway deaths, injuries, and property damages resulting from drunk driving crashes.
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From page 223... ...
214 NEW TRUCKS FOR GREATER PRoDucrlvrrY AND LESS ROAD WEAR will be very unsatisfactory to you and the general public. As members of this Association, you are the nation's, and the world's, top authority and leaders in the highway field.
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From page 224... ...
Appendix A: Looking Ahead from Milepost 1984 215 System into a continuing operation now being referred to as 3R and 4R. For nearly three decades, major emphasis has been placed on the Interstate System, and rightly so.
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From page 225... ...
216 NEW TRUCKS FOR GREATER PRODUCrIVFrY AND LESS ROAD WEAR which were sold in that State, as determined from the State's own records of fuel charges collected from vendors in that State. In this way, each State would receive exactly the same revenue as it would receive had the 6-cent per gallon charge been enacted by its own legislature.
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From page 226... ...
Appendix A: Looking Ahead from Milepost 1984 217 ture; it is a savings; and it is not a tax if used for highway transportation purposes. - WE NEED TO REDESIGN TRUCKS TO FIT THE HIGHWAY It is essential that we stretch our income by lengthening the service life of pavements and bridges already in service and those to be built in the future.
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From page 227... ...
218 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR payload to damage factor in the new vehicle unit could be increased in the order of about 3 to 1 in favor of the new configuration. The net effect of this would be to permit substantial reduction in the cost allocation factors assignable to heavy truck units, and bring them down into a politically reachable level with benefit to both truckers and the highway authorities.
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From page 228... ...
Appendix A: Looking Ahead from Milepost 1984 219 act as leaders in the presently mounting public outcry against drunk driving. It is imperative, of course, that highway safety efforts must also include all other actions which will further the cause, such as use of seat belts and/ or air bags, and strong traffic rule enforcement.
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From page 229... ...
220 NEW TRUCKS FOR GREATER PRODUCFIVITY AND LESS ROAD WEAR way lane capacities, and to reduce air pollution, thereby avoiding probable sanctions by EPA; Strengthen the State-Federal partnership by returning to the concept that it is a joining of exactly equal but complementing partners, and by closing ranks solidly among the State partners so that the Association can consistently speak with one -- and only one -- strong voice; Requesting that our Congressional partners act as national statesmen in highway matters, by refusing to include a clutter of special interest provisions which by their inclusion have lost the entire program for all parties in this last Congress -- and will almost surely do so in future. I believe that AASHTO and the highway program stand this morning at a critical crossroad and interchange, just as we did when last we met here in New Orleans 29 years ago in this same week of 1955.
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From page 230... ...
APPENDIX B Estimation of fatal Involvement Rates for Prototype and Baseline Trucks Fatal involvement rates for the four prototype Turner trucks and the baseline five-axle twin trailer truck and tractor-semitrailer were estimated from the values of the handling and stability characteristics of these trucks (Table 4-2) and the relationships between individual handling and stability characteristics and accident rates developed by Fancher et al.
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From page 231... ...
222 NEW TRUCKS FOR GREATER PRoDucrIvrrY AND LESS ROAD WEAR involvements in the last column of Table B-i) of the five-axle tractorsemitrailer by 0.77 (43.5/56.5)
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From page 232... ...
Appendix B: Estimation of Fatal involvement Rates 223 TABLE B-i FATAL INVOLVEMENTS BY TRUCK TYPE AND HANDLING AND STABILITY CHARACTERISTICS No. of Fatal Involvements per 108 Mi by Type of Accident Rearward Sum of Amplifi- Steering- Involve- Truck Type Jackknife Rollover cation Related ments Baseline Five-axle tractor- semitrailer 6.0 10.8 - 12.2 29.0 Five-axle twin trailer truck 6.5 10.8 5.5 12.2 35.0 Turner Nine-axle double 5.3 10.8 5.5 12.2 33.8 Nine-axle B-train double 5.5 10.8 - 12.2 28.5 Eleven-axle double 5.2 10.8 18.0 12.2 46.2 Seven-axle tractor- semitrailer 5.2 10.8 - 11.8 27.8 Nom: Dashes indicate data not applicable.
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From page 233... ...
APPENDIX C Pavement Cost Methodology The methods and assumptions used to produce estimates of the effects of Turner trucks on costs for new and reconstructed pavements and for. resurfacing and other forms of pavement rehabilitation are described here.
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From page 234... ...
Appendix C: Pavement Cost Methodology 225 most common method remains the application of substantial asphalt concrete overlays to foundation pavement surfaces of either flexible (asphalt concrete) or rigid (portland cement concrete)
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From page 235... ...
226 NEW TRUCKS FOR GREATER PRODUCrIv1TY AND LESS ROAD WEAR reflects factors independent of overlay thickness such as the application of leveling courses, milling, joint repair, subdrainage improvements, and traffic control. Clearly each added ESAL affects overlay thickness and, accordingly, the variable-cost component of an overlay.
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From page 236... ...
Appendix C: Pavement Cost Methodology 227 TABLE C-i ADDED PAVEMENT REHABILITATION COST FOR 10 PERCENT MORE ESALS Added Cost ($ millions per year) Rural Other Urban Other Interstate Rural Interstate Urban Total Flexible pavement 22.57 183.44 7.50 79.78 293.29 Rigid pavement 15.42 14.27 8.24 13.08 51.01 Y is the increase (or decrease)
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From page 237... ...
228 NEW TRUCKS FOR GREATER PRODUCTIVITY AND LESS ROAD WEAR TABLE C-2 PAVEMENT COSTS FOR NEW AND RECONSTRUCTED HIGHWAYS Pavement Type and Highway Classification Typical Structural Number Average Width (It) Pavement Cost ($/mile)
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From page 238... ...
Appendix C: Pavement Cost Methodology 229 loadings is estimated to increase costs for new and reconstructed pavements by $26 million per year. REFERENCES Deacon, J
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From page 239... ...
Study Committee Biographical Information C Michael Walton, Chairman, is currently Bess Harris Jones Centennial Professor and Chairman of the Department of Civil Engineering at the University of Texas.
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From page 240... ...
Study Committee Biographical Information 231 member of the National Academy of Engineering and is an honorary member of the International Association for Bridge and Structural Engineering and the American Society of Civil Engineering. He received the ASCE Ernest E
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From page 241... ...
232 NEW TRUCKS FOR GREATER PR0DUcTIvrFY AND LESS ROAD WEAR William J MacCreery is Deputy Director and Chief Engineer for Highways with the Michigan Department of Transportation.
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From page 242... ...
Study Committee Biographical Information 233 Analysis. He has also been a member of other TRB study committees and review panels.
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From page 243... ...
234 NEW TRUCKS FOR GREATER PR0DuCrIvITY AND LESS ROAD WEAR positions with the Port Authority of New York and New Jersey. She has served as chairman for the TRB Committee on Freight Transportation Planning and Marketing.
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From page 244... ...
1990 TRANSPORTATION RESEARCH BOARD EXECUTIVE COMMITTEE Chairman WAYNE MURI, Chief Engineer, Missouri Highway and Transportation Department, Jefferson City Vice Chairman C MICHAEL WALTON, Bess Harris Jones Centennial Professor of Natural Resource Policy Studies and Chairman, College of Engineering, the University of Texas at Austin Executive Director THOMAS B
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Key Terms
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