The Congestion Mitigation and Air Quality Improvement (CMAQ) Program provides funds to States for transportation projects designed to improve air quality and reduce traffic congestion, particularly in areas of the country that do not attain national air quality standards. Created by the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, the program was reauthorized under the Transportation Equity Act for the 21st Century (TEA-21) in 1997, and again as part of the Safe, Accountable, Flexible, Efficient, Transportation Equity Act: A Legacy for Users (SAFETEA-LU) in 2005. Since 1991, the CMAQ Program has provided funding to over 16,000 projects, and has been a key mechanism for supporting investments that help urban areas meet air quality goals, encourage alternatives to driving alone, and improve traffic flow.
In SAFETEA-LU Section 1808, Congress required the U.S. Department of Transportation, in consultation with the Environmental Protection Agency (EPA), to evaluate and assess the direct and indirect impacts of CMAQ-funded projects on air quality and congestion levels. This study responds to that request by analyzing 67 CMAQ-funded projects, using data supplied by States and metropolitan planning organizations (MPOs) in the Federal Highway Administration (FHWA) CMAQ database. From this information, the study team examined the estimated impacts of these projects on emissions of transportation-related pollutants, including carbon monoxide (CO), ozone precursors oxides of nitrogen (NOx) and volatile organic compounds (VOCs) and particulate matter (PM10 and PM2.5), as well as on traffic congestion and mobility. The study team also conducted additional analyses of the selected set of CMAQ-funded projects to estimate their cost-effectiveness at reducing emissions of each pollutant.
As shown in the set of projects examined in this study, many CMAQ projects help to reduce traffic congestion and improve mobility. Traffic flow improvement projects, which include traffic signalization improvements, incident management programs, and intersection improvements, are designed to improve traffic speeds and minimize delays experienced by drivers. Although many of these projects are small in scope (e.g., an individual intersection improvement), they can have a sizable impact on travel times in specific locations. For instance, among the traffic flow projects that reported travel time savings installation of coordinated signalized intersections along a roadway in Newark, Ohio; two intersection improvements in East Baton Rouge Parish, Louisiana; and traffic signal optimization for arterial highways in Lexington, Kentucky the projects were estimated to save from 702 to 6,360 vehicle hours of delay per day. In total, traffic flow improvement projects represented 42 percent of the CMAQ-funded projects (32 percent of CMAQ funding) during fiscal years (FY) 2000 to 2005, according to the FHWA CMAQ database. In addition to traffic flow improvements, freight and intermodal projects are frequently designed to shift goods movement from trucks to rail, and reduce congestion associated with truck traffic on major freight corridors.
Other projects are designed primarily to enhance mobility by increasing travel options, such as transit, bicycling, walking, and ridesharing. Most of the vanpool, park-and-ride, bicycle/pedestrian, and transit bus service improvement projects examined in this study were estimated to remove from about one hundred to several hundred vehicle trips per day. The magnitude of congestion relief effects from this level of vehicle travel reduction is difficult to assess, and was typically not reported by project sponsors. The primary benefit from these projects is enhanced mobility for travelers, as travelers have a greater range of options to meet their travel needs and have greater access to employment, services, and recreational opportunities. These projects often also have other benefits such as reducing travel costs for individuals and supporting improved quality of life in communities. Mobility can also be enhanced through projects that improve incident management, freeway traveler information, and transit information, which improve travel time reliability and enable people to plan their travel routes, mode choice, and time of travel more effectively.
CMAQ projects typically reduce motor vehicle emissions one of three ways: 1) by encouraging changes in travel behavior that reduce motor vehicle miles traveled (VMT), such as shifts to ridesharing, transit, bicycling, or walking; 2) by improving traffic flow, thereby reducing vehicle idling and stop-and-start driving conditions that are associated with higher levels of emissions; and 3) by implementing technologies to reduce the rate of emissions, such as conversion to alternative fueled buses, or retrofits of diesel vehicles. In addition, in some locations, targeted approaches have been used to reduce wind blown particulate matter from roadways, such as funding street sweepers and application of de-icing chemicals instead of sand.
Although the limited number of projects examined in this study does not allow for definitive conclusions about the effectiveness or cost-effectiveness of different types of CMAQ projects, some general findings are noted below.
First, since many CMAQ projects are small in scale (e.g., a single park-and-ride lot, a bicycle path, a transit shuttle), many of these projects yield small reductions in motor vehicle emissions. Among the projects reviewed in this study, the majority had emissions reduction estimates of less than 50 kg per day of both VOC and NOx, and less than 500 kg per day of CO. In the context of regional air quality concerns, these estimated emissions reductions are generally quite small. The combined impact of multiple projects, and longer-term, indirect benefits (e.g., supporting transit-oriented land use patterns), however, may be more substantial.
Second, a wide variation in estimated emissions effects and cost-effectiveness occurs within project types. Some individual projects showed very strong cost-effectiveness, while other similar types of projects appeared to have poor cost-effectiveness at reducing specific pollutants. Within a given project category, estimated project cost-effectiveness typically varied by a factor of 10 or more (e.g., the most cost-effective new bus service in the set of projects examined was estimated to cost $130,000/ton of VOC removed, while the least cost-effective new bus service was estimated to cost $1.5 million/ton of VOC removed). This high level of variability suggests that local context and project-specific factors are important determinants of the level of emissions reductions that can be expected from projects.
Third, although there is a wide range of estimated emissions benefits and cost-effectiveness at reducing emissions across the set of projects examined, there are some patterns when looking at impacts on individual pollutants. Strategies that aim to reduce vehicle travel, such as shared ride programs, travel demand management, bicycle/pedestrian facilities, and transit improvements, typically reduce emissions of all major on-road transportation related pollutants VOC, NOx, CO, and PM10 and PM2.5 with the largest reductions occurring in ozone precursors and CO. PM reductions from these projects tended to be very small and in many cases were not reported by project sponsors.
Traffic flow improvements, such as signal syncronization and freeway management projects, are typically implemented to improve travel speeds on congested roadways, or to reduce idling time. The emissions effects of traffic flow improvements depend on the overall speed improvement and initial speeds. VOC emissions generally decline with increasing speeds, but NOx and CO emissions can increase at higher speeds. As a result, a traffic flow project could reduce VOC emissions but yield a small increase in NOx, and may have little or no effect on PM.
Finally, diesel emissions-focused strategies can be quite cost-effective at reducing PM emissions. Among the sample projects, dust mitigation-focused projects offered the most cost-effective means for reducing PM10 and PM2.5 from wind-blown dust in locations where they were practical. Diesel engine retrofits and truck idle reduction strategies tended to be the most cost-effective set of strategies for reducing particulate matter outside of the dust mitigation strategies. This is perhaps not surprising, given that diesel vehicles are large emitters of particulate matter, but it is also notable that some diesel engine retrofit projects examined in this study were quite cost-effective at reducing ozone precursors and CO as well. For instance, one type of diesel soot filter used to retrofit transit buses was certified to reduce PM, VOC, and CO emissions each by 60 percent; another technology used in a project to retrofit trash collection trucks was estimated to reduce PM emissions by 80 percent, while also reducing CO by 67 percent and VOC by 95 percent.
In addition to determining the impacts of a sample of CMAQ projects on air quality and congestion, SAFETEA-LU Section 1808 directs an evaluation and assessment of CMAQ projects to "ensure the effective implementation of the program." This report is the first phase of a two phase effort being undertaken by DOT, in consultation with EPA, to address the goals of this evaluation and assessment. This Phase I report focuses on an evaluation of a set of CMAQ projects for the purpose of determining their air quality and congestion benefits, while Phase II involves case studies to further explore approaches to CMAQ project selection and implementation that are effective in achieving air quality improvement and congestion relief.
In the course of collecting data on the selected projects a variety of good practices that States and MPOs use to analyze and select projects for CMAQ funding were revealed. These approaches include: development of standardized templates, calculation guidebooks, and spreadsheets that help to ensure a consistent set of project inputs from project sponsors and to make calculations easier and less prone to error; development of systematic procedures for ranking projects, including consideration of project cost-effectiveness at reducing air pollutant emissions of concern and other factors; and coordination with air agencies and local agencies in the project selection process. The information gathered for this Phase I report was used to help select locations for case study visits in Phase II.
The analysis of emissions reduction cost-effectiveness in this study also provides a possible analytic framework that may help States and MPOs develop their own analysis when considering projects for funding. It is important to note, however, that CMAQ projects also generate other benefits beyond emissions reductions, such as congestion relief, travel time savings, energy savings, enhanced mobility, and other transportation system user benefits, which are not quantified in the emissions reduction cost-effectiveness figures but are important considerations in the overall benefit-cost associated with each project. These many factors also are often important considerations in project selection. Many States and MPOs value the CMAQ Program for the flexible funding it provides to help them address air quality concerns from transportation sources and to help support a wide range of transportation objectives, such as enhancing multi-modal accessibility, improving transportation system reliability, and strengthening community livability.