Federal Highway Administration Resource Center

Efficient Method Developed to Assess Transportation-Related Carbon Monoxide Pollutants

Air quality analysis is a key part of the planning and design process for transportation projects. One of the most studied air pollutants for a transportation project is Carbon Monoxide (CO). Carbon Monoxide is the focus of much of this study because the National Ambient Air Quality Standard (NAAQS) imposes a limit on CO concentrations that result from vehicles operating on a proposed roadway. CO resulting from vehicles operating on a proposed roadway may not increase concentrations that violate the NAAQS.

To conduct a project-level CO analysis is a complex task. Typically the process involves running two separate, complicated computer models. These two computer models are used to compute motor vehicle emission factors and CO concentrations related to a proposed roadway project. State Departments of Transportation (DOTs), working with the Federal Highway Administration, have been developing alternative methodologies to analyze the CO issue in a way that uses available resources efficiently and reduces the time required to conduct a transportation project analysis. One alternative uses the concurrent “worst case” scenario screening strategy. The rationale of this strategy is that if the concurrent worst-case scenario does not produce a violation, other cases will not produce violations. By embedding the worst-case data in the screening program, it eliminates the need to collect site-specific metrological, fleet, and other environmental condition data. Efforts can be concentrated on scenarios that fail the screening test.

The FHWA Resource Center promoted this strategy to the Florida DOT as a way of developing and updating their screening model to meet the new NAAQS. The FHWA Resource Center also provided testing and review of the program.

The Florida Solution

In the early 1990s, the Florida Department of Transportation (FDOT) developed a manual CO screening procedure that was used for all transportation projects. The Project Development and Environment Contract Administrator and Negotiator, achieved a staff time reduction of better than 80 percent when this manual screening procedure was implemented. Recognizing the success of the program, the FDOT converted the manual procedure into a desktop computerized program in the late 1990s. Compared with the manual procedure, the computerized program eliminated the need to manually round down traffic speed and round up traffic volume (in order to obtain a worst case scenario) that was occasionally confusing to new practitioners.

In early 2004, the FDOT’s Environmental Management Office released its latest interim Florida CO Screening Program. According to Mariano Berrios, the Environmental Programs Administrator for the FDOT, this release has incorporated the Environmental Protection Agency’s latest MOBILE6 program. He noted that the program “...will be continuously upgraded as the motor vehicle emission factor model is updated.” Berrios estimates that over the last decade, the computerized CO screening program has saved his agency a minimum of 90 percent staff time on project level CO analysis. At the same time, the screening program has enabled Department staff to concentrate more time on tackling scenarios that failed the screening test. He gave high praise to the FHWA-FL Division Office and the FHWA Resource Center for their “...continuous support, assistance, and leadership role in the development of the screening program.”

“The FDOT and the FHWA work together as one team. We trust each other,” said Berrios.

For more information, contact:

Tianjia Tang
Air Quality Specialist
Air Quality Technical Service Team
FHWA Resource Center, (410) 962-2177
tianjia.tang@fhwa.dot.gov

Joon Byun
Air Quality Specialist
Air Quality Technical Service Team
FHWA Resource Center, (410) 962-0069
joon.byun@fhwa.dot.gov