Evaluating Speed Differences between Passenger Vehicles and Heavy Trucks for Transportation-Related Emissions Modeling

Abstract

Heavy-duty trucks make up only 3% of the on-road vehicle fleet, yet they account for Ͼ7% of vehicle miles traveled in the United States. They also contribute a significant proportion of regulated ambient emissions. Heavy vehicles emit emissions at different rates than passenger vehicles. They may also behave differently on-road, yet may be treated similarly to passenger vehicles in emissions modeling. Input variables to the MOBILE software, such as average vehicle speed, are typically specified the same for heavy trucks as for passenger vehicles. Although not frequently considered in modeling emissions, speed differences between passenger vehicles and heavy trucks may influence emissions, because emission rates are correlated to average speed. Differences were evaluated by collecting average and spot speeds for heavy trucks and passenger vehicles on arterials and spot speeds on freeways in Des Moines, IA, and Minneapolis/St. Paul, MN. Speeds were compared by study site. Space mean speeds for heavy trucks were lower than passenger vehicle speeds for all of the arterials with differences ranging from 0.8 to 19 mph. Spot speeds for heavy trucks were also lower at all of the arterial and freeway locations with differences ranging from 0.8 to 6.1 mph. The impact that differences in on-road speeds had on emissions was also evaluated using MOBILE version 6.2. Misspecification of average truck speed is the most significant at lower and higher speed ranges.

Short-Term Trend Forecast of Different Traffic Pollutants in Minnesota Based on Spot Velocity Conversion

“…IMS is used in the actual traffic flow model, which is very important for accurate traffic modeling [ 34 ], but it’s difficult to obtain directly owing to technical reasons. Hallmark et al [ 35 ] use the chase car method to collect the IMS along the arterial study links. This method works fairly well on arterial and lower-functional class roadways because there is a place to turn around and wait for the test car.…”

Statistical Approach to Estimating Truck Traffic Speed and Its Application to Emission Inventory Modeling

“…In the current practice, a specific speed distribution for truck traffic on freeways is rarely developed, and the speed distribution for the overall freeway traffic is often assumed for all vehicle types. However, different vehicle types (e.g., cars versus trucks) have different operating speeds, which can affect their emission rates (6). For example, in some states the freeway speed limits for trucks are different than those for cars (7 ).…”