The Weaving Length Limit for Short Free Onramps

Onramp merging may be difficult if the onramp weaving/merging length is too short because a driver may find that even merging behind a neighboring large truck on the adjacent outside lane may not be completed safely. Because of insufficient weaving length for onramp acceleration, a slow merged vehicle may be rear-ended by a following vehicle on the outside lane when speed differential between the onramp vehicle and the following vehicle is relatively high. Nevertheless, short onramps at occasions are designed and built when right of way is constrained possibly by a variety of issues. The design onramp weaving length hasn't been well explained physically in various existing guidelines or design manuals. Recently, a design paradigm, where human factors, vehicle dynamics, tire-road friction, and the onramp merging scenarios are integrated into a single framework, has been developed to resolve this merging difficulty. In this paper, the lower limit recommended for onramp weaving length needed for a driver to merge into the freeway traffic successfully is determined based on the physical solutions derived from the paradigm and a physical constraint for avoiding potential rear-end collisions between the slow merged vehicle and the following vehicle on freeway. This weaving length limit sets the minimal weaving length for safer free onramp merging and guides the practitioners/designers who encounter design situations where freeway right of way at onramp is limited.