Oversized/ Overweight Heavy-Duty Vehicle Emission Impact Study

The Dallas-Fort Worth (DFW) region is in violation of federal ambient air quality standards for ozone. The reduction of oxides of nitrogen (NOx) emissions, an ozone precursor, is an important part of achieving regional air quality goals. Heavy-duty vehicles (HDVs) are a major contributor of NOx emissions, contributing a significant proportion of total on-road emissions. Within the HDV population, it is believed that oversize (OS)/overweight (OW) vehicles generate higher levels of emissions than an average HDV due to excessive load on the engine during OS/OW operations. However, there is limited existing information/knowledge on this subject. Therefore, it is important to develop a systematic approach to understanding the contribution of these vehicles to regional emissions and to develop appropriate policies to reduce OS/OW NOx emissions.

The overall goal of the project was to estimate the emissions impacts of OS/OW vehicles operating in the DFW non-attainment (NA) area. The project objective was accomplished through the completion of three main activities:

  • Characterization of OS/OW operations in the DFW region—To determine the impact of OS/OW operations, the research team first looked at the status of OS/OW operations in the area. This task included analyzing currently available data on OS/OW activities in the area, including weigh-in-motion (WIM) data from the Texas Department of Transportation (TxDOT), OS/OW permit data from the Texas Department of Motor Vehicles (TxDMV), and data on commercial vehicle weight-related violations from the Texas Department of Public Safety (TxDPS).

  • OS/OW activity and emissions data collection—To determine the impact of OS/OW activities, the research team collected and analyzed vehicle activity and emissions data from a sample of OS/OW vehicles. The data collection effort included real-world activity data collection and emissions testing using portable emissions measurement systems (PEMS).

  • Analysis and estimation of OS/OW vehicle operations and emission rates—The collected field data were used to develop emission rates for different OS/OW scenarios used in the analysis to quantify the emissions impacts of OS/OW operations in the DFW area. The analyses were based on methods used in the U.S. Environmental Protection Agency’s (EPA’s) MOtor Vehicle Emissions Simulator (MOVES) model.

Oversized/ Overweight Study Final Report [PDF]
Oversized/ Overweight Study Final Report Appendices [PDF]

Appendix A includes a brief history of OS/OW regulations, the current limits set for permitted and non-permitted loads, the type of permits issued in Texas, and the movement restrictions for operating permitted loads.

Appendix B includes information on OS/OW vehicle operations from sources identified during the literature review, including recent studies on OS/OW vehicle operations in Texas.

Appendix C provides the WIM data from the WIM stations in the NCTCOG area by vehicle classification.

Appendix D provides a summary of other studies that evaluated the emissions impacts of OW vehicles.

Appendix E describes the study design plan that guided the data collection efforts that were conducted for the study.

Appendix F describes the data-processing steps used to obtain the emission rate information from the raw emissions data collected during the testing task.

Appendix G covers the unauthorized OS/OW field campaign and results from the data collection.

Appendix H provides all the emission rates calculated from the data collected during the testing of a sample of OS/OW vehicles.
Incoming heavy-duty vehicle to weigh station. Heavy-duty vehicle with large cargo to be weighed at weigh station. Portable emission monitoring set up for test vehicles.
Portable emission monitoring set up for test vehicles. Over-sized heavy- duty vehicle being tested. Overweight heavy- duty test vehicle.
Oversized heavy-duty test vehicle. Overweight heavy- duty test vehicle. Overweight heavy- duty test vehicle.

Texas A & M Transportation Institute

Jolanda Prozzi
(512) 407-1104
j-prozzi@tti.tamu.edu

Staff Contacts: 
Jason Brown
Huong Duong