United States Department of Transportation
i
Truck travel characteristics as an indicator of system condition and performance.
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2011-07-01
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[PDF-10.78 MB]
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Alternative Title:Joint Transportation Research Program Technical Report Series : Civil Engineering
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Edition:Final report.
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Abstract:The effect of trucks on the level of service is determined by considering passenger car equivalents (PCE) of trucks. The
Highway Capacity Manual (HCM) uses a single PCE value for all tucks combined. However, the composition of truck traffic
varies from location to location; therefore a single PCE-value for all trucks may not correctly represent the impact of truck
traffic at specific locations. Consequently, the Indiana Department of Transportation wanted to develop separate PCE values
for single-unit and combination trucks to replace the single value provided in the HCM. Traditionally, equivalent delay and
microscopic simulations have been used to estimate PCE values. In order to facilitate the development of site specific PCE
values, an alternative PCE-estimation methodology was explored in the present study on the basis of lagging headways
measured from field traffic data. The study used data from four locations on a single urban freeway and three different rural
freeways in Indiana. Three-stage-least-squares (3SLS) regression techniques were used to generate models that predict
lagging headways for passenger cars, single unit trucks, and combination trucks. The estimated PCE values for single-unit and
combination truck for basic urban freeways (level terrain) were 1.35 and 1.60, respectively. For rural freeways, the estimated
PCE values for single-unit and combination truck were 1.30 and 1.45, respectively. However, due to the lack of sufficient
quality data for rural freeways, the estimated PCE values for rural freeways are not recommended for use. As expected, traffic
variables such as vehicle flow rates and speed have significant impacts on vehicle headways. The use of separate PCE values
can have significant influence on the LOS estimation. This study also explored regional variation of PCE values. The results
of the likelihood ratio test indicated that it is appropriate to combine data from similar locations (freeway sections at different
geographical locations) for the PCE analysis.
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