Once implemented, it is important to evaluate the effectiveness of the Road Diet. This typically occurs through studying pre- and post-installation crash data, operating speeds, and operational levels of service.

In addition to the basic vehicular operational and safety studies, other conversion impacts an agency may consider evaluating include:

• Traffic diversion to parallel routes
• Transit operations and similar, the two-way left-turn lane operations, and the ability to evaluate "stopped traffic" in one through lane
• Pedestrian and bicycle safety and operations
• Economic impact / livability

In Pasadena, California, a Road Diet improved Cordova Street's multi-modal level of service which is how well a street serves the needs of all users.