Appendix D
Recommendations from Truck Weight Limits Study (1990)

[Transportation Research Board Committee for the Truck Weight Study. Special Report 225: Truck Weight Limits: Issues and Options. TRB, National Research Council, Washington, D.C., 1990, pp. 14–25.]

STUDY RECOMMENDATIONS

The impact analyses conducted for this study support findings from previous truck size and weight studies mandated by Congress. It has been found that increasing truck weights can significantly reduce the cost of goods movement and that cost savings due to more efficient trucks generally exceed the additional pavement and bridge costs incurred by highway agencies. At the same time, other study findings suggest the need for caution in implementing increases in truck weights. Unless the revenues required to cover additional pavement and bridge costs are provided to highway agencies, the condition of the highway system will deteriorate, thereby increasing vehicle repair costs, lowering fuel economy, increasing travel delays and accidents, and adversely affecting driver and passenger comfort. Also, increasing truck weights has both positive and negative effects on safety and traffic operations. On one hand, reduced truck traffic serves to decrease truck-related accidents and congestion. On the other, simply allowing more weight on existing trucks could adversely affect truck operating characteristics and increase accident rates. Further, if user charges do not increase in step with truck costs, inefficient levels of rail diversion might occur. This new truck traffic could cause net losses for the transportation system as a whole if added pavement and bridge costs resulting form diversion exceed savings in transport costs.

In formulating the major recommendations for this study, the committee was guided by the following objectives:

  • To select, from the various proposed changes in truck, weight regulations from industry groups and others, the most practical means



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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Appendix D Recommendations from Truck Weight Limits Study (1990) [Transportation Research Board Committee for the Truck Weight Study. Special Report 225: Truck Weight Limits: Issues and Options. TRB, National Research Council, Washington, D.C., 1990, pp. 14–25.] STUDY RECOMMENDATIONS The impact analyses conducted for this study support findings from previous truck size and weight studies mandated by Congress. It has been found that increasing truck weights can significantly reduce the cost of goods movement and that cost savings due to more efficient trucks generally exceed the additional pavement and bridge costs incurred by highway agencies. At the same time, other study findings suggest the need for caution in implementing increases in truck weights. Unless the revenues required to cover additional pavement and bridge costs are provided to highway agencies, the condition of the highway system will deteriorate, thereby increasing vehicle repair costs, lowering fuel economy, increasing travel delays and accidents, and adversely affecting driver and passenger comfort. Also, increasing truck weights has both positive and negative effects on safety and traffic operations. On one hand, reduced truck traffic serves to decrease truck-related accidents and congestion. On the other, simply allowing more weight on existing trucks could adversely affect truck operating characteristics and increase accident rates. Further, if user charges do not increase in step with truck costs, inefficient levels of rail diversion might occur. This new truck traffic could cause net losses for the transportation system as a whole if added pavement and bridge costs resulting form diversion exceed savings in transport costs. In formulating the major recommendations for this study, the committee was guided by the following objectives: To select, from the various proposed changes in truck, weight regulations from industry groups and others, the most practical means

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 to realize the productivity benefits of increased truck weights while reducing or eliminating possible adverse effects; To make changes in weight limits that would reduce truck accidents and encourage safety improvements in truck design and operation; To provide mechanisms to match user fees with added costs for pavements and bridges; To promote uniformity in the administration of truck weight regulations; To balance the federal interest in protecting the national investment in the Interstate system and facilitating interstate commerce with the interests of states in serving the needs of their citizens and industries; and To develop proposals that are realistic and feasible, and would have a reasonable chance of being implemented. The following are five recommendations that the committee believes to be consistent with these objectives. Recommendation 1: New Bridge Formula Congress should replace the current federal bridge formula on Interstate highways with the following formula: W = 1,000 (2L + 26) for L = 24 W = 1,000 (L/2 + 62) for L > 24 where W is the maximum weight in pounds that can be carried on any group of three or more axles and L is the length in feet of the axle group rounded to the nearest whole foot. States adopting the new bridge formula on Interstates and other roads should identify all bridges that must be posted or replaced as a consequence of the heavier loadings and estimate all additional costs associated with the increase in limits. Taxes on heavy vehicles should then be increased as necessary to cover these additional costs. The recommended bridge formula is the TTI HS-20 formula. This formula, together with federal axle-weight limits, would be applied to vehicles with gross weights of 80,000 lb or less. Recommendation 2 deals with a permit program for vehicles over 80,000 lb and describes how the formula would be extended for these vehicles. Truck costs would decrease by $2.4 billion per year ($2.7 billion per year in transport cost savings less $0.3 billion in higher taxes to cover pavement and bridge cost increases) if all states adopted the recom-

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 mended bridge formula on all their highways. Operators of specialized hauling vehicles (SHVs) such as dump trucks, concrete mixers, and solid-waste disposal trucks would be the principal beneficiaries of this change. Operators of relatively short tractor-semitrailers (such as haulers of tank trailers, dump trailers, and containers) would also benefit. Many states currently have more permissive limits on non-Interstate highways than on Interstates. In these states, increasing the bridge formula on Interstates should serve to attract heavy-truck traffic from other roads. The shift of heavy trucks from non-Interstate to Interstate highways would reduce pavement costs to highway agencies, because on a per-vehicle-mile basis, the pavement wear effects of heavy trucks are much less on thicker pavements. The recommended formula would also cause some operators of heavy three-axle trucks to use four-axle trucks instead. The shift from three-axle trucks to four-axle trucks would be beneficial to pavements, because four-axle trucks cause less pavement wear per ton of freight carried. This shift would occur because the recommended formula provides a greater incentive to add an axle than the current formula. For example, under the current bride formula, 22-ft-long, three-axle trucks can operate at 52,500 lb and 22-ft-long, four-axle trucks can operate at 56,500 lb, a difference of 4,000 lb. Under the recommended bridge formula, the three-axle truck would be controlled by axle weight limits to 54,000 lb (20,000 lb on the single axle and 34,000 lb on the tandem axle) and the four-axle truck could operate at up to 70,000 lb (depending on its axle spacings), a difference of 16,000 lb. Replacing the current bridge formula with the recommended formula would increase the number of bridges that must be posted or replaced. Currently, about 120,000 of the nation’s 600,000 bridges are posted. If all states adopted the recommended bridge formula on all their highways, the number of posted bridges would increase by about 22,000—4,000 on primary highways and 18,000 on nonprimary highways. On an annual basis, the cost to reconstruct all 22,000 bridges would be about $350 million a year. As a practical matter, many states would choose to post rather than reconstruct some of these bridges (particularly those on low-volume nonprimary highways). Whereas posting results in lower bridge costs to highway agencies, it also increases the circuitry of travel for heavy trucks and might make the use of certain heavy trucks impractical because they cannot conveniently reach their destinations. Thus, if highway agencies posted rather than reconstructed many bridges, both truck cost savings and the added costs for bridges should be reduced.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 In summary, the committee found that, even with a cautiously high estimate of the added bridge costs, adoption of the recommended bridge formula by all states would result in a new savings of over $2 billion per year and would reduce congestion and accidents involving heavy trucks. The impact analyses conducted for this study indicate that increases in weight limits beyond the recommended formula would, more likely than not, result in additional savings; however, the committee’s ability to anticipate all the important consequences of such increases is limited. The bridge formula recommended here is the result of striking a balance between the objectives of maximizing net savings and minimizing uncertainty about the consequences of changes in limits. Recommendation 2: Special Permit Programs Congress should broaden the process for exemptions so that it would not be necessary for states to claim grandfather exemptions in order to permit vehicles to operate over the federal gross weight limit of 80,000 lb. Rather, all states should be allowed to establish permit programs for heavier vehicles, provided that such programs included provisions to control the characteristics and operations of permit vehicles. Key features of the special permit programs would be designated routes, maximum weights, fee structures, and safety restrictions for permit vehicles. Designated Routes. States should designate routes over which permit vehicles may operate, and all bridges on proposed routes should be checked to ensure that they can accommodate permit vehicles. Maximum Weights. The maximum weight for permit vehicles over 80,000 lb should be no greater than that given by the current federal bridge formula for vehicles with up to nine axles. How the new bridge formula given in Recommendation 1 could be combined with the current formula for vehicles over 80,000 lb is shown in … Table ES-3. States with grandfather exemptions that currently allow vehicles to operate over federal axle limits or at weights greater than those shown in Table ES-3 should be allowed to continue to do so only if they meet other requirements of the special permit process. Fee Structures. States should establish fee structures for permits that are adequate to cover any increase in highway agency costs resulting from permit vehicles and all costs associated with administration and enforcement of permit programs.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 TABLE ES-3 Recommended Bridge Formula Limits for Axle Groups Maximum Weight (kips) Axle-Group Length (ft) Maximum Weight (kips), 3 or More Axles   Maximum Weight (kips) Axle-Group Length (ft) 5-6 Axles 7 Axles 8 Axles 8 42.0 37 80.5 81.5 87.0 9 44.0 38 81.0 82.0 87.5 10 46.0 39 81.5 83.0 88.5 11 48.0 40 82.0 83.5 89.0 12 50.0 41 82.5 84.0 89.5 13 52.0 42 83.0 84.5 90.0 14 54.0 43 83.5 85.0 90.5 15 56.0 44 84.0 85.5 91.0 16 58.0 45 84.5 86.5 91.5 17 60.0 46 85.0 87.0 92.5 18 62.0 47 85.5 87.5 93.0 19 64.0 48 86.0 88.0 93.5 20 66.0 49 86.5 88.5 94.0 21 68.0 50 87.0 89.0 94.5 22 70.0 51 87.5 90.0 95.0 23 72.0 52 88.0 90.5 95.5 24 74.0 53 88.5 91.0 96.5 25 74.5 54 89.0 91.5 97.0 26 75.0 55 89.5 92.0 97.5 27 75.5 56 90.0 92.5 98.0 28 76.0 57 90.5 93.5 98.5 29 76.5 58 91.0 94.0 99.0 30 77.0 59 91.5 94.5 99.5 31 77.5 60 92.0 95.0 100.5 32 78.0 61 92.5 95.5 101.0 33 78.5 62 93.0 96.0 101.5 34 79.0 63 93.5 97.0 102.0 35 79.5 64 94.0 97.5 102.5 36 80.0 65 94.5 98.0 103.0   66 95.0 98.5 103.5   67 95.5 99.0 104.5   68 96.0 99.5 105.0   69 96.5 100.5 105.5   70 97.0 101.0 106.0   71 97.5 101.5 106.5 NOTE: Axle Group Length is the distance between the extremes of any group of three or more consecutive axles. Maximum weights over 80,000 lb are permitted only under special permit on designated routes. All vehicles are also subject to a single-axle limit of 20 kips and a tandem-axle limit of 34 kips. (1 kip = 1,000 lb.)

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267   Maximum Weight (kips) 9 or More Axles Axle-Group Length (ft) 5-6 Axles 7 Axles 8 Axles 9 or More Axles 93.0 72 98.0 102.0 107.0 112.5 93.5 73 98.5 102.5 107.5 113.0 94.0 74 99.0 103.0 108.5 113.5 94.5 75 99.5 104.0 109.0 114.0 95.0 76 100.0 104.5 109.5 115.0 95.5 77 100.5 105.0 110.0 115.5 96.0 78 101.0 105.5 110.5 116.0 97.0 79 101.5 106.0 111.0 116.5 97.5 80 102.0 106.5 111.5 117.0 98.0 81 102.5 107.5 112.5 117.5 98.5 82 103.0 108.0 113.0 118.0 99.0 83 103.5 108.5 113.5 118.5 99.5 84 104.0 109.0 114.0 119.5 100.0 85 104.5 109.5 114.5 120.0 100.5 86 105.0 110.0 115.0 120.5 101.5 87 105.5 111.0 115.5 121.0 102.0 88 106.0 111.5 116.5 121.5 102.5 89 106.5 112.0 117.0 122.0 103.0 90 107.0 112.5 117.5 122.5 103.5 91 107.5 113.0 118.0 123.0 104.0 92 108.0 113.5 118.5 124.0 104.5 93 108.5 114.5 119.0 124.5 105.0 94 109.0 115.0 119.5 125.0 106.0 95 109.5 115.5 120.5 125.5 106.5 96 110.0 116.0 121.0 126.0 107.0 97 110.5 116.5 121.5 126.5 107.5 98 111.0 117.0 122.0 127.0 108.0 99 111.5 118.0 122.5 127.5 108.5 100 112.0 118.5 123.0 128.5 109.0 101 112.5 119.0 123.5 129.0 109.5 102 113.0 119.5 124.5 129.5 110.5 103 113.5 120.0 125.0 130.0 111.0 104 114.0 120.5 125.5 130.5 111.5 105 114.5 121.5 126.0 131.0 112.0  

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Safety Restrictions. States should use the permit process aggressively to promote safety by establishing restrictions on permit vehicles and vehicle components and by revoking the permits of carriers with serious or repeated safety violations. FHWA and the National Highway Traffic Safety Administration should review their current regulations and establish additional regulations as necessary to ensure that vehicles operating under the permit programs would contribute to improved highway safety. Specific topics to be considered in establishing special safety regulations for permit operations include the following: Power requirements for acceleration and hill climbing; Driver qualifications; Accident reporting and insurance requirements; Braking systems; Connecting equipment such as fifth wheels, pick-up plates, kingpins, and hitch connections; and Axle width, tires, and rims. FHWA should work with states and the trucking industry to establish a review and approval process for state permit programs to ensure that (a) permit fees are commensurate with added highway costs, (b) safety regulations for permit vehicles are implemented, and (c) strict revocation procedures are in effect for permit holders who violate the terms of their permits. Congress should enact legislation to authorize this expanded role for FHWA. One of the key findings of this study is that, although grandfather exemptions provide substantial benefits to the economy of a state through the use of more productive vehicles, the grandfather test itself is an arbitrary and inequitable means for determining such exemptions. This recommendation would allow states that cannot claim grandfather exemptions to establish permit programs for these more productive vehicles operating over the 80,000-lb federal limit on gross weight. The committee recommends a permit process rather than simply the elimination of the 80,000-lb limit for several reasons: Most states that currently allow vehicles over 80,000 lb under grandfather exemptions do so only under special permit programs, with designated networks for permit vehicles. A permit process with a carefully designed fee structure provides a mechanism for covering possible increases in pavement or bridge costs caused by heavier vehicles.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Permit processes strengthen the hand of the state in enforcing weight and safety regulations. They give states considerable latitude to impose special conditions to make enforcement easier (e.g., special markings on vehicle) and permits can be revoked for repeated or severe violations. Permit processes allow states to require safety-related improvements to vehicle components as a condition for using more productive trucks. If the 80,000-lb limit were eliminated, five-axle doubles could operate at up to 92,000 lb, depending on their length. Such vehicles are undesirable at weights over 80,000 lb, because they cause relatively high pavement wear per unit of freight hauled. Under a permit program, these vehicles could be banned or charged higher permit fees commensurate with the damage they add to pavements. There is a substantial body of experience with permit programs for vehicles over 80,000 lb, with limits very similar to those called for by the committee. Currently, 13 western states have permit programs for vehicles over 80,000 lb, with weights controlled by the federal bridge formula and axle limits. Several other states in the East and Midwest allow such vehicles to operate on turnpikes. To ensure that permit revenues cover added costs, states wishing to establish new permit programs should compile the following information: (a) all routes over which permit vehicles would be allowed to operate, (b) bridge replacements and any other improvements necessary to accommodate permit vehicles on these routes, (c) a schedule and cost estimates for making these improvements, (d) estimates of increases in administrative and enforcement costs due to the program, (e) a fee schedule for permits to be issued under the program by vehicle configuration and operating weight, (f) estimates of permit revenue by year, (g) other changes in highway user revenues expected to result from the permit program (e.g., increases or decreases in fuel tax revenues or registration fees), and (h) a comparison of estimated costs and revenues by year. Special permit operations for heavier vehicles will have implications for federal highway program costs as well as state costs. Since it is proposed that state permit fees be collected to cover the full costs of added pavement and bridge improvements necessitated by special permit operations, the issue of federal costs must be considered. If the improvements to accommodate permit vehicles continue to be eligible for federal participation, some adjustment to federal cost responsibility

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 assessments and program apportionments may be necessary to maintain equity. States with many deficient bridges might face a large up-front cost if they wished to open many routes to permit vehicles. This problem might be addressed in the following ways: Initially restrict permit vehicles to routes without deficient bridges and then apply permit revenues as they become available to expand the routes open to permit vehicles. Restrict weights for permit vehicles based on an analysis of the load-bearing capacity of individual bridges. Institute a temporary increase in existing highway user taxes for heavy trucks (e.g., diesel fuel, registration fees) to build up revenues that could then be used to make improvements necessary to open routes to permit vehicles. Once the improvements have been made and permit revenues have become available, the increase in existing taxes could be rolled back. Develop innovative public-private arrangements for funding improvements. For example, carriers might be given a discount on permit fees paid several years in advance. States would then not have to draw on existing revenue sources to advance the money for making the improvements. Recommendation 3: Grandfather Rights Congress should take no action to restrict grandfather rights that have already been claimed by states, but should prevent future expansion of these claims. Many vehicles that can now be operated on Interstates only under grandfather exemptions could, if Recommendations 1 and 2 are adopted by Congress, be operated in all states. For example, the longer combination vehicles (LCVs) that now operate at weights over 80,000 lb in those western states with grandfather exemptions to the federal gross weight limit could operate in any state that chose to establish a permit program for such vehicles. Nonetheless, the implementation of Recommendations 1 and 2 would not completely render moot the issue of grandfather exemptions. Currently, 19 states have axle-weight limits that are exempt under the grandfather clause. Also, several states exempt certain types of vehicles from the bridge formula. For example, Michigan allows vehicles over 80,000 lb that exceed Formula B by a considerable amount, and Arkansas and Pennsylvania apply

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Formula B only to vehicles over 73,230 lb. Further, the 1982 Surface Transportation Assistance Act (STAA) increased the latitude of states regarding grandfather claims based on legislation that was effective in 1956 or 1974. The committee believes that Congress should put a halt to new claims of grandfather rights for weights in excess of federal axle limits and the recommended weights presented in Table D-1. However, a decision by Congress to eliminate grandfather rights that have already been claimed by states could present a hardship to truckers who have purchased equipment to take advantage of these rights and could adversely affect transport costs for commodities that are important to the economies of states. In such cases, the committee believes that the question of whether grandfather clauses should remain in place is best left up to the states themselves. Recommendation 4: Increased Enforcement A portion of the revenues from overweight permits should be used to increase efforts to enforce truck weight laws, particularly on non-Interstate highways, which are more susceptible to damage by illegally overweight trucks. These efforts should include more weight enforcement personnel in the field, more use of portable scales, use of weigh-in-motion scales to screen potentially overweight trucks, and higher fines and penalties for repeated offenses. Congress should ask FHWA to conduct a study directed toward improved enforcement of truck weight laws. The study should address (a) direct enforcement (apprehension and arrest), (b) adjudication and penalties, (c) education of judges and prosecutors, and (d) research and management of enforcement activities. The study should identify specific techniques for improved enforcement and assess these techniques in terms of their impact on the magnitude and frequency of overweight trucks, personnel requirements and other costs to enforcement agencies, and possible burdens on the trucking industry. Increased enforcement would benefit highway agencies and highway users by decreasing the cost required to repair damaged pavements and bridges. Increased enforcement would also benefit truckers and shippers who operate within weight limits by eliminating the competitive advantage of those who operate illegally. Finally, increased enforcement would reduce the number of accidents caused by dangerously overweight trucks.

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Regulation of Weights, Lengths, and Widths of Commercial Motor Vechicles: Special Report 267 Recommendation 5: Regional Cooperation in Standardizing Limits and Permit Practices States should pursue opportunities for standardizing limits and permit practices at the regional level. More uniform weight limits and permit practices would simplify the problem of designing, selecting, and loading trucks for use in interstate commerce. Total uniformity is probably not practical, given regional variations in commodities carried, terrain, density, and highway and bridge design. Nonetheless, there are important opportunities for standardizing limits and permit practices at the regional level. Good examples of past efforts along these lines include (a) ongoing efforts in western states to standardize aspects of the special permits allowing operation of LCVs and (b) an agreement by New England states to implement a common set of procedures for issuing oversize and overweight permits for trucks engaged in interstate transport of nondivisible loads.