This study evaluated the effectiveness of a dynamic late lane merge system (DLLMS) installed at work zones on I-94 during the 2006 construction season in southern Michigan. The system used microwave traffic sensors, wireless communications, and a series of portable dynamic message signs (DMS) to direct drivers when to merge. When congestion was detected in the open lane (lane without the tapered closure) and average traffic speeds dropped below a preset threshold level of 35 mi/hr, dynamic message signs upstream were activated to advise drivers to “Use Both Lanes to the Merge Point” to preempt queuing and improve traffic flow.
Evaluators compared freeway performance data collected at the DLLMS site with data collected at the control site equipped with only traditional work zone controls. A statistical analysis was performed to quantify the differences in mean travel time delay, the mean travel speed, and crash frequencies, and evaluate the economic viability of the system.
Results from t-testing indicated there was a statistically significant difference in performance at sites with and without DLLMS.
|Description (congested PM peak)|
|Average travel time (sec/10,000 ft/veh) (pre-taper)|
|Average travel speed (mi/hr) (pre-taper)|
|Average number of stops per 10,000 ft/veh (pre-taper)|
|Average delay (sec/10,000 ft/veh) (pre-taper)|
|*Average total throughput (veh/hr)|
|*Average percentage of merges at the taper|
|*Average percentage of merges prior to the taper|
A benefit-to-cost analysis conducted during the study. Results indicated the DLLMS is cost effective where the dollar value of motorists time can exceed $4.85 per hour. The analysis consisted of multiplying the value of motorist time by the travel time saved, adding the related fuel savings, and comparing this value to the actual cost of the system. With respect to travel time benefits, travel time savings were converted to a monetary value based on estimates of what drivers would be willing to pay for travel time savings. Note that safety benefits were not included in the analysis since the calculated change in crash frequency was not statistically significant.
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