Modal vehicle activity on freeways and freeway on-ramps: An assessment of the oxides of nitrogen emissions impacts resulting from changes in vehicle operating mode due to ramp metering systems

The Clean Air Act Amendments of 1990 and the most recent US Department of Transportation funding bill, the Transportation Equity Act for the 21st Century, signed in 1999, both contain provisions that encourage the use of transportation control measures (TCMs) to help reduce motor vehicle emissions. The primary goal of these provisions is to assist the attainment efforts of communities that do not comply with the National Ambient Air Quality Standards. One widely implemented class of TCMs throughout the US is traffic management strategies that improve traffic flow. In 1992, 36 percent of the Congestion Mitigation and Air Quality program funds were obligated to traffic flow improvement projects. Ramp metering systems are one type of traffic flow improvement strategy that is gaining popularity in many urban areas throughout the US.; This research analyzed the vehicle modal activity on freeway on-ramps and mainline sections under ramp metered and non-metered conditions. Under the premise that vehicle emissions are a function of modal activity (as well as vehicle parameters and operating environment), such as idle, cruise, and acceleration rates, this research used modal activity data, collected in the field to assess the air quality implications of ramp metering systems.; The Mobile Emissions Assessment System for Urban and Regional Evaluation (MEASURE) model was used to evaluate the air quality impacts of the Atlanta ramp metering system. The results produced from the MEASURE model were also compared with emissions estimates produced from the USEPAs MOBIL5b emissions rate model. The MOBILE5b model is an average speed model that is not sensitive to vehicle modal activity.; In addition to producing vehicle NOx emissions estimates, this research assessed the parameters that influence vehicle model activity on freeway on-ramps and in turn vehicle emissions. Roadway design, traffic volume, and metering plans were tested for their impact on modal activity. This information allowed for the development of ramp meter operation guidelines that will lead to metering systems that optimize operations and minimize air quality impacts.