Impacts of Roadway Access Management on Air Quality, Energy Consumption, and Greenhouse Gas Emissions

Focus Area

Air Quality


Air Quality







Research Idea Scope

Roadway access management has been shown to be highly effective in terms of improving both traffic safety and traffic flow. Crash rate reductions of between 40 and 50 percent are well-documented in before and after research where access management has been implemented. Improvements is travel speed and traffic flow are also well documented. It is not uncommon for the peak hour mean travel speed of urban arterials to improve by 10 miles per hour after access management has been implemented. The 2005 Texas Transportation Institute (TTI) Urban Mobility Study includes access management as a potentially valuable treatment in reducing motorist delay on urban arterials; the study estimates potential gains of 46 million lost travel hours in 85 urban areas if access management were to be aggressively implemented.

Relatively little is known about the potential for access management to reduce emissions by motor vehicles and therefore to impact air quality. It is well-known that motor vehicles traveling at a near constant speed of 35 to 50 miles per hour tend to produce significantly fewer air pollutant emissions than those involved in “stop and go” traffic. (This is thought to be true for CO and VOC emissions; the optimal speed for NOx is lower.) So in theory, access managed roadway facilities should generate air quality improvements. The same is true for energy efficiency and therefore greenhouse gas emissions. Maximum vehicle fuel efficiency and green house gas emissions appears to take place at a speed of 35 to 55 miles per hour. Since access management tends to produce urban arterial roadways that operate at free flow speeds of 35 to 50 miles per hour, there could be demonstrable energy efficiency, air quality, and greenhouse gas emissions benefits from wider implementation of access management treatments. Access management may allow transportation systems to operate in a more sustainable manner as a result.

This research is intended to document the environmental and energy efficiency benefits, if any,  of implementing roadway access management. The results should be useful to State DOTs, environmental quality agencies, metropolitan and regional planning agencies, and local governments. The results will also be helpful in updating the TRB Access Management Manual.

Suggested By

TRB Research Needs Database, AHB70, Access Management