Urban Freeway On-Ramps

Abstract

In this paper the influences of the ramp flow on the freeway flow are deemed invasive influences because the freeway vehicles' priority is violated and the freeway flow is interrupted. Understanding of the invasive influences of the freeway entry process helps to promote efficient and safe operations of the main-line facility and to identify more straightforward indicators of level of service (LOS) for freeway on-ramp segments. First, on the basis of field observations conducted at three on-ramp sites along I-35 within the greater Kansas City, Kansas and Missouri, metropolitan area, ramp merging behavior of vehicles in platoons was identified as the direct cause of invasive influences on the freeway flow. Then, the significance of the invasive influences was evaluated in accordance with the evasive events performed by freeway drivers. These evasive events, instigated by merging conflicts, include slowdown and lane change actions. Finally, more straightforward LOS indicators were recommended for improving the current (2000) Highway Capacity Manual LOS evaluation procedure for freeway on-ramp segments.