Field Data for Evaluating 2010 Highway Capacity Manual Operational Analysis Methodology for Interchange Ramp Terminals

Abstract

Interchange ramp terminals provide connections between various highway facilities (freeway–arterial, arterial–arterial, freeway–freeway, etc.), so their efficient operation is essential. NCHRP Project 3–60 developed analysis methods for evaluating the operational performance of signalized interchange ramp terminals. Those methods were based primarily on simulated data. Further research used collected field data to evaluate the interchange analysis methodology developed under NCHRP Project 3–60 to identify application limitations and to suggest improvements. Data were collected at eight sites representing various types of interchanges with different geometric and traffic characteristics. Video cameras, mounted on existing poles on the side of the road and on nearby buildings, were used to gather traffic operation data, including demand, lane utilization, and queue length at each site. The research evaluated both individual analytic model components (such as lane utilization factors and internal queue length) and the performance of the interchange (reflected in average queue lengths and control delay). Overall, the models performed well. However, large discrepancies were observed when operating conditions of the interchange were close to capacity. The queue length prediction at the beginning of the upstream arterial or ramp phase was calibrated to modify the effective green time estimation. A new lane utilization model was based on field data for a four- or five-lane external arterial approach where the two leftmost lanes were extensions of the downstream dual left turn lanes. The findings of the work were incorporated into the 2010 Highway Capacity Manual.