SAFETY AND CAPACITY EVALUATION OF THE INDIANA LANE MERGE SYSTEM

The entry to a work zone is critical for traffic smoothness and safety because of the discontinuation of one or more lanes. The Indiana Lane Merge System (ILMS) was designed to implement dynamic lane change control at work zone entries by encouraging drivers to switch lanes well upstream of the discontinuous lane taper, thereby reducing the number of aggressive lane changes at the taper. At the time of this research, the ILMS had not been implemented on a large scale at rural freeway work zones. The Indiana Department of Transportation (INDOT) wanted to do a complete safety and capacity evaluation of the system before implementing it statewide. The safety of a system is usually evaluated by close examination prior to and following the installation of the system, i.e., before and after studies. Since crashes are rare and random occurrences, it would take a long time (usually 5-10 years) before the safety study can be completed. Another safety indicator that is used by a number of safety researchers is traffic conflicts. Unfortunately, safety benefits expressed in traffic conflicts (unlike crashes) cannot be converted to a monetary value. In this study, a new method combining crashes and conflicts is proposed. The relative change in the number of conflicts with and without the system is first established, which is then assumed to be equivalent to the relative change in the number of crashes. This value is then multiplied by the expected number of crashes without the system to obtain the expected crash reduction using the new system. Crash prediction models without ILMS and conflict models with and without ILMS were developed. In addition, a capacity evaluation was conducted to estimate the capacity impacts of ILMS. All the models were integrated and a detailed sensitivity analysis was performed by using a spreadsheet-based application that was developed using Visual Basic. The software program also serves as a tool for INDOT personnel to estimate the expected safety and monetary benefits for a given work zone. Sensitivity analysis results are summarized in the ILMS guidelines, which are based on daily vehicle profiles, directional distributions, and heavy vehicle profiles from rural freeways in Indiana. The estimated total benefits showed minimal variation in this study with respect to changes in vehicle profiles and directional distributions of traffic flow.

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