Merging Vehicles and Lane Speed-Flow Relationship in a Work Zone

In addition to closed merge lanes as physical bottlenecks of work zones, traffic oscillations caused by merging vehicles at multiple locations could reduce work-zone capacity. This study took a step-wise procedure to reveal spatial distributions of merging vehicles along work zones and their influence on speed-flow relationships of lane traffic flows. Field data showed that inserting vehicles from merge lanes could spread their influence over adjacent unclosed through lanes. Moreover, with increases in total volume, merging vehicles could choose their inserting positions further upstream of the work zone, which could induce oscillations near the insertion point. At the identified upstream bottlenecks, capacity drop was found in speed-flow diagrams of through-lane traffic, but it was not found in the diagrams of merge-lane traffic flows. Lack of sufficient demand and special merging behaviors on merge lanes could be attributed to the distinct speed-flow relationship. Two-part piecewise regression models were developed to fit the speed-flow relationships of uncongested and congested flows of through lanes. By comparing the estimated speed-flow models, it was found that when a queue is forming, the extent of the capacity drop and speed reduction is different for through lanes. Queue discharge uses different lengths of time on through lanes and multiple merging locations