Measurement and Analysis of the Operations of Drayage Trucks in the Houston Area in Terms of Activities and Exhaust Emissions

The effects of exhaust emissions on public welfare have prompted the US Environmental Protection Agency to take various actions toward understanding, modeling, and reducing air pollution from vehicles. This study was performed to better understand exhaust emissions of heavy-duty diesel-powered tractor-trailer trucks that operate in drayage service, which involves the moving of shipping containers to or from port terminals. The study involved the use of portable emissions measurement systems (PEMS) to measure both gaseous and particulate matter (PM) mass emission rates and record various vehicle and engine parameters from the test trucks as they performed their normal drayage service. These measurements were supplemented with port terminal gate entry/exit logs for all drayage trucks entering the two Port of Houston Authority container terminals. The datasets were combined to analyze model year characteristics of drayage trucks over time, evaluate port visit frequencies and durations, assess geographic distributions of trucks that perform port service, and estimate the pollutant emissions related to drayage operations. When compared to certification results, measured pollutant emissions generally exceeded certification standards in terms of nitrogen oxides and PM, although this difference may be partly because these vehicles were not tested on certification cycles but rather actual in-use operation. The findings of this work indicate that less than 3.5 percent of gaseous drayage truck emissions are released during operation within port terminals, as drayage trucks operate at higher engine loads during their extensive travels throughout the region around the port.