Variable Speed Limit Compliance Impact on Bottleneck Lane Changing Pattern

Abstract

Variable Speed Limit (VSL), an active traffic demand management (ATDM) strategy, is widely exercised to improved freeway operations by influencing collective driving pattern during congested condition. Since high traffic flow coupled with elevated lane changing rate can onset congestion on freeway bottleneck locations, VSL benefits should be correlated with its’ proficiency in modifying lane changing patterns of traffic stream. Additionally, different compliance level (CL) of VSL should have different impact on congestion reduction and thus on lane changing pattern. Existing macroscopic lane changing models are proved to be inadequate to address the influence of two major aspects of traffic flow variables (speed difference and density difference) on lane changing decisions. Since most of the earlier lane changing models considered either one of them as lane changing incentive, their estimation was found to be impressionable by roadway traffic condition. This study introduces a model framework to approach the problem using simple microscopic lane-changing concept within a macroscopic model. The proposed model considers both speed and density difference as lane-changing incentive based on prevailing roadway condition. The resulting macroscopic model was calibrated and validated with empirical data. The results showed that the proposed model was able to competently reproduce the expected lane changing flows at different traffic state. The proposed lane changing model was applied to estimate lane changing from field observations at a recurrent bottleneck section for ‘without’ and ‘with’ VSL control cases. The primary objective of this research is to study the effect of optimal VSL control on collective lane changing by modeling several compliance levels to VSL and also to study field observations in order to identify the transformation in lane changing behavior due to VSL Control. In this study, several CL to VSL strategies has been modeled to quantify the transformation in lane changing pattern at different compliance level. The model data analysis have shown definite correlations between CL and lane changing flow. Model output also demonstrated that mobility benefits can be achieved through VSL control with improved compliance. To investigate this conjecture, the field test data of Advisory VSL control on Whitemud Drive, Edmonton, Alberta, Canada have been analyzed. The research findings demonstrated that voluntary compliance to VSL has insignificant implications on compliance behavior and consequently collective lane changing pattern. To obtain substantial advantage, the VSL compliance improvement will be necessary which will eventually bring favorable change in collective lane changing pattern.