Traffic Analysis for Highway-to-Highway Interchanges on Automated Highway Systems: Congestion in Absence of Dedicated Ramps

Abstract

Special connector ramps linking the automated lanes at automated highway–to–automated highway interchanges may be needed to enable continuous automated driving between two crossing highways. Although a typical cloverleaf configuration has only two levels and is more amenable for such additions, the sharp curvature of this design usually imposes constraints on traffic speed and flow. Because of these constraints, most highway–to–highway interchanges in urban areas have straighter lanes but tend to involve three or more levels. Building the additional connector ramps to accommodate eight high-speed turning movements at an area where the geometry is already complex could be difficult or costly. Therefore, proponents of automated highway systems (AHS) face a major dilemma. This dilemma is studied, including the impact of not providing automated connector ramps on the manual and AHS traffic on manual lanes at or near a highway-to-highway interchange. It is shown that, with a typical cloverleaf design, in the absence of the additional connector ramps, any moderate to heavy AHS-changing traffic could severely disturb the flow of through traffic, seriously exacerbate congestion, and possibly cause a traffic breakdown at the interchange area. These effects will most likely negate any mainline throughput benefits for which an AHS is designed.