Note that the above findings are based on the empirical data collected over a period of eight weeks on one sample roadway segment. Although the overall findings that VSL can be — effective in increasing traffic speed and throughput over a highway segment plagued by recurrent congestion are quite convincing, how to maximize the effectiveness of VSL under various — traffic congestion patterns and resource constraints remains a challenging issue. More experimental studies to improve our understanding of the interrelations between driver responses and VSL control strategies are essential for the development of reliable implementation guidelines. 6.2 Recommendations for Future Research and Experimental Work As one of the pioneering studies for exploring the VSL control for recurrent highway congestion, the research results have revealed some imperative issues that need to be addressed prior to the development of an operational manual for VSL applications and the comprehensive deployment of such a control strategy. Each of those issues is briefly presented below: What criteria and/or guidelines should be used to select target roadway segments suited to the deployment of VSL controls to mitigate their recurrent congestion? Such guidelines should discuss highway geometric features, the spatial and temporal distribution of traffic flow speeds, time-varying volume patterns between upstream and downstream segments during the peak hours, the length of the bottleneck segment versus the entire target segment for speed transition, the transition distance between free-flow and congested flow speeds, and the theoretically available capacity at the most congested location. How many advisory points should be selected for speed transition between free-flow and congested speeds? The guidelines for this issue should consider all
Note that the above findings are based on the empirical data collected over a period of eight weeks on one sample roadway segment. Although the overall findings — that VSL can be effective in increasing traffic speed and throughput over a highway segment plagued by recurrent congestion — are quite convincing, how to maximize the effectiveness of VSL under various traffic congestion patterns and resource constraints remains a challenging issue. More experimental studies to improve our understanding of the interrelations between driver responses and VSL control strategies are essential for the development of reliable implementation guidelines. 6.2 Recommendations for Future Research and Experimental Work As one of the pioneering studies for exploring the VSL control for recurrent highway congestion, the research results have revealed some imperative issues that need to be addressed prior to the development of an operational manual for VSL applications and the comprehensive deployment of such a control strategy. Each of those issues is briefly presented below: What criteria and/or guidelines should be used to select target roadway segments suited to the deployment of VSL controls to mitigate their recurrent congestion? Such guidelines should discuss highway geometric features, the spatial and temporal distribution of traffic flow speeds, time-varying volume patterns between upstream and downstream segments during the peak hours, the length of the bottleneck segment versus the entire target segment for speed transition, the transition distance between free-flow and congested flow speeds, and the theoretically available capacity at the most congested location. How many advisory points should be selected for speed transition between free-flow and congested speeds? The guidelines for this issue should consider all