Evaluation of Downstream Merge Behaviors Resulting from Driver Lane Choice: A Driving Simulator Study

With the ever-increasing demand to add roadway capacity in a safe and efficient manner, the application of auxiliary through lanes (ATLs) at intersections has increased in recent years. Despite the potential capacity-related benefits, ATLs also introduce the potential for unique driver operation tactics, leading to challenging merge scenarios downstream of signalized intersections. Furthermore, the benefits of increasing capacity are only realized when drivers are making decisions that balance the utilization of the ATL and the adjacent continuous through lane. Moreover, balancing lane utilization upstream of an ATL signalized intersection may introduce an improvement in safety and operations in merging conflicts downstream. Previous research investigated the effectiveness of ATLs through microsimulation and field studies. This research employed two full-immersion driving simulation studies. The initial experiment was conducted using simulation technology to evaluate aspects of driver behavior associated with lane utilization at ATLs. Lane utilization of the ATL significantly increased when the driver was informed of the fundamental design concept, ultimately improving capacity. The second experiment was based upon the results of the initial experiment, coupled with ongoing research evaluating alternative merge signage. Specifically, the second experiment aimed to evaluate downstream merge signage that could mitigate some of the behaviors resulting from the less than optimal lane utilization for ATLs. With an emphasis on improving intersection performance, the results from this paper suggest that the implementation of alternative merging signage may lead to improved merging behavior.

Utilization of Auxiliary Through Lanes at Intersections of Four-Lane, Two-Way Roadways

To increase the capacity of through traffic at signalized intersections, additional lanes with limited length—called auxiliary lanes—are added to the roadway at the intersection. Because of their limited length, as well as other factors, these lanes are not as fully utilized as other continuous through lanes. Research was undertaken with two objectives: ( a) to observe and identify the level of use of auxiliary through lanes added at intersections of four-lane, two-way roadways; and ( b) to study the effects of auxiliary lane length, right-turn volume, and through/right-turn lane group delay on the level of their use. Lane-use data collected during 1,050 saturated cycles at eight signalized intersections with different auxiliary lane lengths were used to accomplish research objectives. All factors investigated—auxiliary lane length, right-turn volume, and stopped-delay—were found to contribute significantly to the use of auxiliary lanes at 0.01 level. The level of each factor’s contribution, however, was dependent on the level of the other two. Lane use of nearly one to seven straight-through vehicles per cycle, depending on levels of factors investigated, was observed at the study locations. Longer auxiliary lanes, lower right-turn volumes, and excessive approach delays encouraged the use of auxiliary lanes by straight-through vehicles. The range of lane utilization adjustment factors ( fLU-factors) calculated from field data was 0.73 to 0.82, which is lower than the 1997 Highway Capacity Manual default value of 0.91 for a three-lane through/right-turn group.

Utilization of Auxiliary Through Lanes at Signalized Intersections with Downstream Lane Reductions

The capacity of multiple through lanes at signalized intersections depends on the distribution of traffic within these lanes, with equal lane distribution corresponding to maximum capacity. However, traffic characteristics, land use, and geometric factors usually prohibit this from occurring. Although the 1994 update of the Highway Capacity Manual considers the case of continuous through lanes at signalized intersections, the default values provided do not address situations in which lane reduction takes place downstream of the intersection. Lane distribution data obtained in the field can remedy the situation but for existing conditions only. This research employed the concept of captive and choice lane users in modeling lane use for intersection configurations with a single continuous through lane and an “auxiliary” through lane, which is continuous upstream of the intersection but is dropped downstream of it. Stepwise multiple regression was performed on data collected at sites in Tennessee to ascertain those factors significantly affecting auxiliary lane use. These factors were found to be ( a) right turns off the facility at the intersection, ( b) total left turns off the facility downstream of the intersection, ( c) right turns onto the facility in the first 122 m (400 ft) upstream of the intersection, ( d) right turns off the facility in the last 152 m (500 ft) of the auxiliary lane, ( e) downstream auxiliary lane length, and ( f) the existence of left-turn bays or two-way continuous left-turn lanes downstream of the intersection. For the configuration studied, lane distribution data often differed considerably from the default values given in the Highway Capacity Manual.