Assessment of Fuel Economy Technologies for Medium and Heavy ...

or non-existent. One exception is that some regulations may lead to the use of technologies that
add modestly to the weight of the vehicle, which will modestly reduce cargo capacity on a weight
basis. This will only be an issue for shipments that ―weigh out‖ (i.e., are limited by the maximum
load allowed), and not those that ―cube out‖ (i.e., are limited by volume). It is also conceivable
that some truck purchasers might purchase smaller engines due to the higher cost of meeting
more stringent fuel economy standards. If this is the case, the purchaser has still determined that
the reduced performance will not be a significant detriment to their ability to conduct business,
and therefore, by definition, there is no significant impact to shippers or to the overall economy.
(vi) Congestion Impacts
Key Question: If regulations reduce truck performance and/or reduce or increase truck VMT,
what are the potential implications for congestion
Background: Section (ii) describes how the demand for long-haul trucking could increase if fuel
economy regulations effectively reduce the net operating cost of long-haul trucking. Truck
demand is estimated to increase by 3.2 to 15 billion VMT (an increase of 2.2 to 10.5 percent),
depending on the technology alternative selected, the prevailing national truck price elasticity
and rail cross price elasticity, regulation, and technology response. While degraded truck
performance could also impact congestion, the concurrent white paper produced by ERG
suggests that the impacts of fuel economy regulations on truck performance will be minimal, if
any.
The remainder of this analysis focuses on basic freeway sections because fuel economy
regulations are most likely to affect long-haul truck traffic, which spend the vast majority of their
time on freeways. (Trucks have a significant impact on congestion at other traffic control
locations, such as signalized and unsignalized intersections, merge sections, and
freeway-to-freeway off-ramps, but the data to analyze these impacts is not readily available.) In
the highway capacity manual (HCM), in basic freeway analysis, trucks are represented as
―passenger car equivalents‖ (PCE). 20 The PCE concept is meant to capture the effect that heavy
vehicles have on traffic flow on a freeway because heavy vehicles occupy more space, travel more
slowly up steep grades and more quickly down them, accelerate more slowly, brake more slowly,
and change lanes more slowly than passenger cars. Furthermore, different passenger car
operators react differently to the presence of trucks; for example, following further behind trucks
than cars. An increase in the total truck traffic PCEs on the road could be attributable to a
number of effects, most significantly an increase in total traffic, although there could also be
modest impacts if trucks have lower power output, higher weight, or regulations that encourage
class-shifting.
The HCM increases the PCE for trucks based on roadway conditions such as grade, number of
lanes, distance to roadside obstructions, and width of lanes. It does not, however, distinguish
between truck PCEs under congested and uncongested conditions. FHWA simulated the effect
of combination trucks as part of its Truck Size and Weight Study to estimate how effective truck
PCEs change based on the weight-to-horsepower ratio of the truck itself, the grade of the
roadway, the road type, geography, and congestion levels. They did not estimate the impacts of
20
Transportation Research Board, Highway Capacity Manual, Washington, D.C., 2000.
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