Integrating Off-Ramp Spillback Control with a Decomposed Arterial Signal Optimization Model

Congestion downstream of a freeway off-ramp often causes the traffic queue to spill back to the main line and thus reduces freeway capacity at the interchange area. To prevent queue spillback, this study proposes a two-stage control model that optimizes the signal plans on an off-ramp connected arterial. The first stage of the model optimizes the green splits for the target intersections and their common cycle length with a specified queue length constraint. The second stage of the model decomposes the target arterial into two groups of segments: one for accommodating the heaving off-ramp turning flows and the other mainly for through traffic on the local arterial. With field data from the freeway interchange in Chupei, Taiwan, the study evaluates the performance with extensive simulation experiments and demonstrates the effectiveness of the proposed model for preventing queue spillbacks at the off-ramp and for minimizing the resulting impact on the freeway main line.