The effect of weaving maneuvers on operation of a free right-turn lane at ramp terminals

Service interchange ramp terminals provide access from the local highway or urban street system to the freeway. In urban areas, the ramp terminals at the arterial road are usually signalized for separation of all high-volume conflicting movements. If right-turn or other movements exiting from the ramp terminals are high, a free right-turn lane, which improves operations for right-turn and through exiting traffic, is sometimes provided at the ramp terminals with an exclusive lane for right-turn vehicles on a departure leg. If the ramp terminal is closely followed by the next downstream intersection, weaving maneuvers will occur since some vehicles make a right turn at the ramp terminal and make a left turn at the downstream intersection. These weaving vehicles usually slow down or stop on the free right-turn lane in order to find an acceptable gap in the arterial road traffic. These slowing or stopping vehicles may cause safety and operational problems. This research evaluates the effect of these weaving maneuvers on the operations of a free right-turn lane at the ramp terminals. To provide a means for evaluating free right-turn lane operations, a linear regression model was developed to predict the delay on the free right-turn lane caused by stopped or slowed vehicles planning on making a weaving maneuver. The variables for this model were arterial through volumes, weaving volumes, number of lanes, and ramp spacing within the interchange. The regression model was based upon the results of the CORSIM traffic simulation model that was calibrated using field data obtained from the study site in College Station, Texas. Once the predicted model was developed, the model validation was performed using the field data to check the accuracy of its prediction. A statistical measure was performed for quantifying the difference between the observed and predicted delay on the free right turn lane. From the research results, it was concluded that the weaving maneuvers influence the operation of a free right-turn lane and cause delay on the free right-turn lane.