TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 178: Assessment of Auxiliary Through Lanes at Signalized Intersections describes a project that investigated the operational, safety, and design characteristics of auxiliary through lanes (ATLs) at signalized intersections.

The project resulted in the development of guidelines for the evaluation and application of ATLs that were published as NCHRP Report 707: Guidelines on the Use of Auxiliary Through Lanes at Signalized Intersections.