Observed Distribution Patterns of On-Ramp Merge Lengths on Urban Freeways

Abstract

Three on-ramp sites with moderate to high volumes of through and merge traffic along I-35 within the greater Kansas City, Kansas and Missouri, metropolitan area were selected for investigation of the distribution patterns of the merge lengths of ramp vehicles. On the basis of the observed merging behaviors, merge vehicles were categorized into three types: free merge (FM), challenged merge (CM), and platoon merge (PM). The field data were analyzed with specifically developed software. The results show that (a) FM vehicles merge onto a freeway at arbitrary locations, (b) CM vehicles require traveling a longer distance before a safe merge, and (c) PM vehicles follow a natural smooth path and force themselves onto the mainline traffic within a certain area of a merge lane. The 85th-percentile merge length of all ramp vehicles was further observed to be related to the CM volume, the PM volume, and the average speed of the freeway right-hand first lane. Finally, the potential applications of these findings were discussed, with an example illustrating how to use the 85th-percentile merge length to determine the minimum merge lane length for an urban freeway on-ramp.

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