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Final Report Now Available: Diesel Inspection and Maintenance Pilot Program

In the Dallas-Fort Worth (DFW) region, approximately 49 percent of on-road emissions of nitrogen oxides are attributable to heavy-duty diesel vehicles (Texas Commission on Environmental Quality, DFW 2008 Eight-Hour Ozone Attainment Demonstration State Implementation Plan Revision for the 2017 Attainment Year Appendix B), yet these vehicles are excluded from the State’s Inspection and Maintenance (I/M) Program. To evaluate the feasibility of incorporating diesel vehicles into the I/M Program, NCTCOG partnered with the Texas Department of Transportation, Texas A&M Transportation Institute (TTI), the Texas Department of Public Safety, and the University of Denver to test the second prototype of an emissions testing technology called the On-Road Heavy-Duty Emissions Measurement System (OHMS).

This study was Phase 2 of a previous pilot study conducted in 2012 by TTI. Phase 2 focused on conducting further testing and design refinements from the pilot study and comparing other technologies that could be integrated with the OHMS or as an alternative to OHMS design. Once the OHMS design was finalized, TTI implemented the updated OHMS design for a field study in New Waverly, Texas. Nearly 1,000 heavy-duty diesel vehicles were included in the study and the final report can be found at

Pictured above: The updated OHMS design for emission testing located at the New Waverly Weigh Station.

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