Michigan Study Assessed Design and Sign Message Effectiveness for Work Zone Driveway Assistance Devices Using Field Tests and a National Survey.
Statewide, Michigan, United States
Effective Signing Strategies and Signal Displays for Work Zone Driveway Assistance Devices (DADs)
Summary Information
Traditional traffic control for work zones that include a single lane closure on a two-lane, two-way roadway often utilizes flaggers or temporary traffic signals such that only a single direction utilizes the open travel lane at any time. As a part of the Smart Work Zone Deployment Initiative (SWZDI), researchers studied driveway assistance device (DAD) display designs and developed guidelines related to the use of DADs. A DAD is an experimental traffic control treatment that help drivers safely enter a one-lane, bi-directional work zone from a driveway or minor side street, by using alternating left and right flashing arrows to inform drivers of the permitted flow direction and a steady red indication when unsafe to enter. Researchers used a nationwide online survey of 1,015 motorists to study comprehension of DAD signal configurations and auxiliary sign messages, and in summer 2020, conducted a field study of 10 minor access points along a suburban work zone section on US Route 31 in northern Michigan. The field study evaluated the effects of five different auxiliary signs on driver compliance when utilized with a DAD, based on a total of 2,258 exiting vehicle observations obtained from elevated video cameras.
- Implement auxiliary signage in conjunction with the DAD signal to provide clearer direction on actions drivers need to take. Both the survey and field tests found that including the prominent “WAIT” text at the top of the sign could improve sign message effectiveness. For example, the sign message “WAIT Turn Only in Direction of Arrow” had the highest rate of safe movements among all signs tested in this study. Survey results also indicated that messages using “Turn” rather than “Yield” for the flashing yellow arrow indication would better convey the proper action. A “No Turn On Red” sign below the DAD improved understanding of the proper response for the steady circular red indication to 87.6 percent compared to 80.6 percent without signage.
- Avoid using the red-over-yellow arrows signal head configuration which had lower communications effectiveness ratings. Survey results indicated higher effectiveness ratings in communicating driver actions with horizontal and doghouse (a single red above the yellow arrows) configurations, as compared to separate left and right columns with red over yellow arrows.
- Optimize the timing at each DAD to influence optimized gap and dwell times. The DAD signal should be timed to allow platoon clearance but deter drivers from turning on red.
- Provide left and right storage lanes to improve DAD operations at higher-volume access points. The findings from the field study revealed that queued motorists may become impatient and make unsafe movements if vehicles blocked the front of the queue.
