Travel Characteristics of Urban Freight Vehicles and Their Effects on Emission Factors

Abstract

This study collected local commercial vehicle data in Knox County, Tennessee, from the U.S. Postal Service (USPS) and two companies engaged in package pickup and delivery (PUD). Another urban commercial vehicle data set with a wider spectrum of freight companies was obtained from North Carolina for comparative analysis. The two data sets were analyzed to develop two sets of values for input parameters for the U.S. Environmental Protection Agency's MOBILE6 model. Statistical tests permitted four aggregated vehicle usage classes to be formed. Two runs of MOBILE6 modeled the two commercial vehicle data sets in their entirety. Four additional runs modeled each vehicle usage class individually through the use of average speed and starts per day specific to the driving pattern of each class. Differences between the values of input parameters and emission factors based on data collected by this study and those based on the default values of MOBILE6 are discussed. Commercial vehicles examined by this study indicated higher annual mileage accumulation rates than the default values. Also their vehicle miles traveled and engine start distributions by hour of day varied considerably from the default values, occurring primarily between the two daily peak traffic periods (morning and evening). The study found higher volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxide emission factors than in default runs for USPS vehicles, whose driving pattern resulted in lower-than-default average speed. Higher VOC and CO emission factors were found for gasoline and diesel package PUD vehicles due to lower-than-default average speeds and higher-than-default starts per day.