A study conducted by the U.S. Department of Transportation Intelligent Transportation Systems shows that electronic toll collection systems reduce environmentally harmful emissions at toll plazas.

The results of the study examined changes in mobile emissions after electronic toll collection systems were installed at three major toll plazas outside Baltimore, Md. The system used toll-tag readers and in-vehicle transponders to automatically execute toll transactions as vehicles passed through tollbooths.

Based on field observations of traffic conditions at the Fort McHenry Tunnel, the Baltimore Harbor Tunnel and the Francis Scott Key Bridge, computer models were used to simulate traffic patterns and quantify emissions of hydrocarbons (HC), Carbon monoxide (CO) and Nitrogen oxides (NOx), before and after the system was deployed.

Three scenarios were simulated to evaluate the impacts on air quality. The first scenario represented conditions prior to the deployment (early spring of 1999). The second scenario represented conditions as the market penetration rates reached 21-28% (summer of 1999), and the third scenario represented conditions as market penetration rates reached approximately 50% (2001).

Results:
A comparative analysis of the pre- and post-deployment scenarios showed that the electronic toll collection system reduced HC and CO emissions by 40-63%, and reduced emissions of NOx by approximately 16%.

Intelligent Transportation Systems U.S. DOT - January 3, 2006