This study develops a comprehensive guideline to estimate the traffic diversion rates and capacity reduction for work zones. The analysis of the traffic diversion patterns with data from past work zones in the metro freeway network resulted in a set of the diversion-estimation models that relate the diversion rates at entrance and exit ramps with the traffic delay on a freeway and alternative route travel times. The interrelationship between diversion and work-zone delays has led to the development of an iterative process, where a freeway simulation model interacts with the diversion-estimation models until a convergence is achieved between diversion and resulting freeway delays. Freeval is adopted in this study as the simulation tool for freeways. The test results of the iterative process with the work zone data showed promising results in determining both the diversion rates and freeway delay for a given work-zone. In particular, the test results with the work zone data not included in developing the process show the similar level of accuracy as those whose data were included. This indicates the transferability of the proposed methodology to new work zones. Due to the types of the work zones used in developing the diversion models, the iterative process developed in this study can be applicable to only “two-to-one” lane reduction cases in estimating the diversion rates for the mainline exit flows, while the diversion rates at entrance ramps can be determined with the current version. The capacity analysis of the lane-closure sections performed in this study has indicated that the geometric conditions of work zones, such as lane-closure configuration, lane-width, and median/shoulder type, directly affect the capacity values of a given work zone. The resulting guideline includes a set of the suggested capacity values for the work zones with two-to-one lane reduction. The above iterative process and capacity analysis results are integrated into a comprehensive guideline, which can provide practical assistance to field engineers in estimating the traffic diversion rates and capacity reduction for work zones. Future study needs to include the expansion of the diversion estimation process to the work zones with different lane-closure configurations other than two-to-one lane-reduction, e.g., three-to-two, by collecting and analyzing additional work-zone data. The capability of estimating diversion rates for multiple time periods would be needed for analyzing large-scale work zones. The advantages of adopting a microscopic network-simulation tool instead of the current macroscopic model can also be studied. Finally, a userfriendly, computerized process for the whole iterative process needs to be developed for efficient estimation of diversion rates by field engineers. (Author/publisher)
Samenvatting