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31 The M.o.U. includes some specific dimensional limits that with a gross weight greater than 36,287 kg (80,000 lb). There did not exist previously in some or all provinces. Several car- have been no broad changes since 1991, though a number of riers specified dimensions to the nearest inch of the actual specialized configurations have been defined. metric dimension, and the manufacturers built the vehicle, There have been a number of research studies addressing either a tractor or trailer, to the specified dimension plus or truck size and weight issues, and the following are briefly minus an inch or so. This was not a problem when the error reviewed here: was within the legal range, but it did become a problem the other way. The first step was to measure the vehicle as accu- · The Turner Proposal (67), rately as possible. For wheelbase, axle spacings, or inter-axle · The U.S. Department of Transportation (U.S.DOT) Com- spacings, this meant ensuring the vehicle was as straight as prehensive Truck Size and Weight (CTSW) Study (68), possible, measuring both sides carefully to allow for axles that · Review of Truck Size and Weight Limits (69), and set up not square to the vehicle, and then averaging the results · The Western Uniformity Scenario (70). from the two sides. When a vehicle was found that was spec- ified correctly but built out of tolerance, some provinces 3.3.2 The Turner Proposal would issue a special permit for it at no charge, while others simply recommended that a copy of the specification be car- Former Federal Highway Administrator Francis Turner ried in the cab. It was recommended that carriers specify di- suggested a new approach to truck size and weight regulation mensions at least 0.025 m (1 in.) on the safe side of any spec- in an address to the American Association of State Highway ified dimension, to ensure vehicles would be built within the and Transportation Officials (AASHTO) in 1984. The Turner limits, including any manufacturing tolerances. Proposal envisaged trucks with lower axle and axle group In general, the M.o.U. has increased the proportion of ve- weights, on more axles than current vehicles, and with greater hicles in each province that are standard configurations. It has allowable gross weights. AASHTO asked the Transportation become almost unnecessary to measure vehicles that evidently Research Board to establish a committee to conduct a com- conform to the M.o.U., as they can reasonably be presumed to prehensive study of the proposal and to advise states on its have been built to comply with the specified dimensions. merits (67). The committee designed a package of changes in size and weight limits, safety restrictions, and procedures pertaining 3.3 U.S. Truck Size and to bridge deficiencies, routing, and enforcement as a means Weight Regulation of implementing the Turner proposal. The committee antic- ipated that Turner trucks, if adopted in most or all states, 3.3.1 Introduction would reduce the cost of shipping freight and would not In order to identify areas in which the Canadian truck size compromise safety. It further anticipated that the total cost of and weight experience might be of benefit to the United States, maintaining the road network would be reduced, although it is necessary to understand the U.S. truck size and weight en- pavement-wear savings would be partially offset by higher vironment, and recent truck size and weight research in the bridge costs. States would incur a fiscal risk because upgrad- United States. ing bridges would have to begin before Turner trucks could Truck size and weight limits were the sole jurisdiction of begin extensive operations, so pavement savings would lag the states up to 1956. Since then, federal legislation has been behind the investment in bridges. instrumental in shaping the sizes, weights, and configurations During the study, the committee altered the original con- of trucks allowed today, some nationally, and others on des- cept in two ways. First, the adoption of Turner trucks by states ignated and more limited networks. The Federal-Aid High- would be completely voluntary, and motor carriers could way Act of 1956 established truck size and weight limits for either continue to operate currently legal trucks or they could the Interstate system, but states with weight limits higher than adopt the newer trucks. Second, the new trucks would be re- the new federal limits were allowed to retain those limits quired as a fleet to be as safe, or safer, than existing trucks and under grandfather authority. Federal weight limits were in- be compatible with roadway design on major roads through- creased in 1974 to help offset a large increase in fuel prices, out the country. but not all states adopted the higher limits. The STAA of 1982 The most common large truck was a 5-axle tractor- required all states to allow twin trailers and required all states semitrailer with a maximum weight of 36,287 kg (80,000 lb) to allow weights and dimensions of certain configurations not and length of 15.24 to 19.81 m (50 to 65 ft). The most com- less than specified values. The Intermodal Surface Trans- mon multi-trailer combination had two 8.53-m (28-ft) portation Efficiency Act (ISTEA) of 1991 limited the author- trailers, 5 axles, a maximum weight of 36,287 kg (80,000 lb), ity of states to increase use of double trailer combinations and an overall length of about 21.34 m (70 ft). The truck
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32 configurations considered by the study utilized a wide range effects of large trucks is such that the impacts cannot be fore- of possible values for axle weights, length limits, and other cast with certainty beforehand. vehicle characteristics in order to achieve the best perfor- Major recommendations pertaining to Turner trucks were mance in terms of productivity, pavement wear, bridge costs, made regarding: weight, dimensions, and equipment; route and safety. The study considered the following prototype restrictions and driver qualifications; deficient bridges; state, Turner truck configurations: federal, and industry coordination; enforcement and moni- toring; and finance. The report encouraged a national program · A 7-axle tractor-semitrailer with maximum weight of perspective and coordination to make the Turner proposal 41,277 kg (91,000 lb) and length of 18.29 m (60 ft); successful, and the recommendations needed to be imple- · A 9-axle A-train double trailer combination with two mented as a package for the proposal to achieve its intended 10.06-m (33-ft) trailers, 51,710-kg (114,000-lb) maximum benefits. weight, and 24.69-m (81-ft) overall length; The study recommended the following maximum axle · A 9-axle B-train double with similar dimensions and group weights: single axle--6,804 kg (15,000 lb), tandem weights to the preceding prototype; and axle--11,340 kg (25,000 lb), tandem drive axle--12,700 kg · An 11-axle A-train double trailer combination with maxi- (28,000 lb), tridem axle--40,000 lb, and 4-axle group-- mum weight of up to 63,957 kg (141,000 lb). 22,680 kg (50,000 lb). The study established a "bridge for- mula" but there was no "cap" or gross combination weight The Turner study evaluated the impacts of these proto- limit applied. Restrictions stipulated in this section related to types on productivity, safety and traffic, bridges, and pave- ensuring a high level of safety were as follows: ments. The nine-axle A-train double trailer combination was considered the most attractive to motor carriers. The adop- · Minimum and maximum trailer lengths, with a kingpin- tion of Turner trucks nationwide was expected eventually to to-rear-axle limit; result in a 23% reduction of the existing combination truck · Antilock brakes on power units; miles, within 5 to 10 years after the trucks became legal. · Minimum speed on all grades; Turner trucks would attract 2% of freight ton-miles from ex- · B-train configuration required for tank trucks; and isting trucks, and 4% of rail ton-miles. Combining the larger · Newer coupling options should not be adopted until the payloads of the new vehicles with the rail diversion would appropriate standards could be developed. yield a slight net decrease in the annual U.S. miles of combi- nation truck travel. Turner trucks were expected to offer a The report recommended against allowing Turner trucks small decline in truck crashes and a small reduction in truck on routes with substandard bridges or on routes that would interference with traffic flow, because the total annual miles otherwise not adequately serve the needs of these trucks in of combination-truck travel would decline. The major cost to terms of safety or traffic operations. Each state should estab- highway agencies resulting from the Turner proposal would lish a mechanism with criteria to develop a route network. be bridge costs. The proposal would require replacement of The report recommended a minimum of 5 years experi- 7,000 Interstate and primary highway bridges, 4% of the total, ence for drivers, with a driver training course on the specific at an estimated total cost of $2.8 billion, with an additional vehicle being considered. $4.1 billion to replace bridges on the non-primary system, The report encouraged states to develop a plan for replac- although some of these routes would not be critical. There ing deficient bridges through development of a priority rank- would also be an additional $110 million per year needed for ing for replacement, a timetable, a finance plan, short-term new bridge construction and $28 million annually once measures for mitigating bridge obstacles, postings more ac- Turner truck traffic reached its long-term level. Savings in curately based on actual capacities, and use of Turner trucks pavement wear was estimated to reach $729 million annually as the actual design vehicle. once Turner trucks reached long-term levels. Turner trucks Coordination would be essential between state, federal, would reduce the annual highway agency costs to maintain and industry components to make the Turner truck operat- the road system by $326 million, once they reached full uti- ing environment viable. Turner trucks would exceed the cur- lization nationwide. rent 36,287-kg (80,000-lb) gross weight cap applied to most The estimates of impacts of Turner trucks were considered of the Interstate system, except for grandfather exemptions. highly uncertain at the time of this study. Although some of AASHTO would need to seek action by Congress to direct the the uncertainty might be less today, it still exists. Also, the re- U.S.DOT to adopt standards defining Turner trucks. States port points out that some of the uncertainty, especially per- would also need to make the necessary changes to allow for taining to safety, could be minimized by strict rules for oper- Turner trucks and to determine routing and bridge posting ating the proposed trucks. The state of knowledge of the practices. State motor carrier advisory committees and shippers