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would need to provide input related to bridge postings, lim- mensions. These tools were intended to provide a measure of
its, and enforcement. the relative safety compared to vehicles in widespread use.
The Turner study recommended that carriers declare their The impacts of various vehicles on safety, productivity, and
intent to operate Turner vehicles at the time of registration or so forth were assessed for five truck size and weight scenarios.
when applying for a special permit. The owner should also cer- These scenarios were
tify that vehicles and drivers comply with all restrictions that
apply to Turner trucks. States should develop procedures that · Uniformity--Imposed federal weight limits on all non-
would help the state monitor and document factors associated network highways and removed grandfathered vehicles
with Turner truck safety. These procedures could include li- under provisions in current federal law. This resulted in a
censing and certification procedures for driver qualification and gross weight cap of 36,287 kg (80,000 lb) on all national
training, developing report forms that identify the number of network routes, and LCVs were impractical.
trailers and axles, and collecting travel data to be used for mon- · North American Trade--Increased allowable tridem axle
itoring weight compliance, use, and safety of Turner trucks. loads to be more consistent with limits in Canada and
Recommendations pertaining to finance included initial Mexico. Tridem loads of 19,958 kg (44,000 lb) and 23,133 kg
bridge expenditures and truck taxes. The principal financial (51,000 lb) were considered.
obstacle to implementing the Turner proposal would be the · LCVs Nationwide--Allowed LCVs on a nationwide net-
cost to remove bridge deficiencies on major truck routes. The work, with the largest LCVs restricted to a designated net-
study recommended that states should seek congressional work, but triples combinations and doubles with 10.06-m
action on setting program funding levels to match the accel- (33-ft) trailers allowed more flexibility.
· H.R. 551--Three provisions related to federal truck size
erated spending for bridges in the early years after adoption
of Turner trucks. This accelerated spending would be offset and weight limits in this scenario would phase out trailers
longer than 16.20 m (53 ft), would freeze state grandfather
by reduced need for pavement maintenance in later years.
rights, and it would freeze weight limits on noninterstate
Truck taxes assessed by states, toll authorities, and the federal
portions of the National Highway System.
government should reflect the differences among all vehicles.
· Triples Nationwide--Allow triple trailer combinations to
If adjustments are needed, they should provide the appropri-
operate nationwide at a gross weight up to 59,875 kg
ate incentives to operators to choose trucks that are the most
(132,000 lb), the same as in LCV nationwide scenario.
efficient, considering both highway and truck operating costs.
Table 2 summarizes the estimates of the diversion of truck
3.3.3 The Comprehensive Truck Size traffic for each scenario. VMT is vehicle miles of travel, in
and Weight Study millions, and rail car-miles are also in millions. The four sce-
narios allowing heavier vehicle weights all indicate large per-
The U.S.DOT's Comprehensive Truck Size and Weight centage reductions in travel by 5-axle tractor-semitrailers and
Study was not primarily focused on any policy initiative, but large increases in LCV travel. Total VMT for all scenarios is
more on development and testing of analytical tools to estimate greater than current levels due to the predicted overall growth
potential diversion of traffic from one type of truck to another, in the national economy over the study period. Impacts of the
or diversion between truck and rail, if truck size and weight lim- various truck size and weight scenarios on infrastructure,
its were changed. The study also made significant improve- shipper costs, and the environment were related to the traffic
ments over previous studies by explicitly considering inventory diversion estimates in Table 2.
and other logistics costs to shippers in making transportation Table 3 shows the estimated percentage change from the
decisions. Impacts of proposed size and weight changes consid- base case for key areas. The study assumed that all bridges
ered to be most critical were: safety, productivity, infrastructure with stress exceeding that underlying the Federal Bridge For-
(pavements, bridges, and geometrics), traffic congestion, envi- mula would ultimately be replaced, which is consistent with
ronment, and railroads (68). previous truck size and weight studies sponsored by U.S.DOT
Because safety was and continues to be a contentious issue and TRB, though some states commented that it may overes-
in relation to increased truck size and weight limits, this study timate bridge-related costs. Safety impacts are not shown in
included an extensive review of past safety studies and devel- Table 3 due to the difficulty in determining the impact of pro-
oped a consensus of results. The reason previous studies posed changes on safety. As noted elsewhere, crash rates for
might still continue to raise doubts is that previous crash sta- vehicles with increased weight and length would need to be
tistics come from operating environments that are signifi- extrapolated from environments that are significantly differ-
cantly different from those proposed. Therefore, this study ent from some of those being considered.
developed tools to evaluate stability and control properties of The CTSW study showed significant productivity gains for
different vehicle configurations at different weights and di- each scenario that allowed heavier vehicle weights, with the
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Table 2. Estimated diversion for selected vehicle configurations for
CTSW scenarios.
6-axle
Vehicle 5-axle Tractor-
Tractor- LCVs Total Truck 2 Rail
Class semitrailer
semitrailer
Car-
Scenario VMT % VMT % VMT % VMT % %
miles
Base Case 83,895 6,059 1,517 128,288 25,555
Uniformity 91,205 8.7 3,519 -41.9 542 -64.3 132,351 3.2 NA3 NA3
N.A. (1) 22,274 -73.5 6,209 2.5 49,837 3185 114,671 -10.6 24,354 -4.7
N.A. (2) 24,997 -70.2 6,246 3.1 47,453 3028 114,632 -10.6 24,073 -5.8
LCVs 19,611 -76.6 NA1 NA1 40,980 2601 98,562 -23.2 20,546 -19.6
H.R. 551 83,915 0.0 6,051 -0.1 1,517 0.0 128,311 0.0 NA3 NA3
1 1
Triples 23,405 -72.1 NA NA 39,647 2513 102,400 -20.2 24,533 -4.0
Note:
N.A. (1)--North American Trade Scenario 1, with 19,958-kg (44,000-lb) tridem axle (90,000 lb gross
vehicle weight).
N.A. (2)--North American Trade Scenario 2, with 23,133-kg (51,000-lb) tridem axle (97,000 lb gross
vehicle weight).
1
Six-axle tractor-semitrailers were not included in the two scenarios involving LCVs.
2
The total does not equal the sum of the three vehicle classes shown in the table because other vehicle
classes included in the total are not shown in the table.
3
Potential diversion from truck to rail under the Uniformity and H.R. 551 Scenarios could not be
estimated because of lack of data on rail pricing.
Source: Reference (68).
greatest gains generated by LCVs. There were concerns that strated that they are safe, that LCVs improve productivity,
LCVs would increase infrastructure costs, adversely affect and that current grandfather laws often result in LCVs hav-
railroads, and possibly reduce safety. States differed consid- ing to operate on roadways that are not as safe as the Inter-
erably on changes in truck size and weight and on changes re- state system. Still other states wanted to increase the gross
lated to LCVs. Many states that did not currently operate weight for 6-axle tractor-semitrailers, and also for single-unit
LCVs were opposed to relaxing restrictions on their use. trucks like dump trucks, garbage trucks, and specialized haul
States that allowed LCVs on state highways generally favored vehicles. Such vehicles would not be expected to cause addi-
removing the LCV freeze and liberalizing the rules under tional pavement damage on Interstate highways, nor would
which LCVs operate. They maintained that LCVs have demon- they increase the cost of geometrics.
Table 3. Estimated impacts of scenarios
(percent change from base case).
N.A. N.A.
Uniformity LCV H.R. 551 Triples
Trade (1) Trade (2)
Pavement
-0.3 -1.6 -1.2 -0.2 0 0
Costs
Bridge Costs -13.0 +33.1 +42.2 +34.4 0 +10.4
Geometric
0 +13.3 +13.3 +965.0 0 0
Costs
Congestion
+0.6 -1.2 -1.2 -2.9 0 -7.6
Costs
Energy Costs +2.1 -6.2 -6.3 -13.8 0 -12.8
Shipper Costs +3.0 -5.1 -7.0 -11.4 0 -8.65
Rail
N/A -42.8 -49.7 -55.8 N/A -38.2
Contribution*
Note:
N.A. Trade (1)--19,958-kg (44,000-lb) tridem axle;
N.A. Trade (2)--23,133-kg (51,000-lb) tridem axle.
*The amount of rail revenue available to pay fixed costs after freight service (variable) costs have been
covered.
Source: Reference (68).
