Effective Signing Strategies and Signal Displays for Work Zone Driveway Assistance Devices (DADs)

Project Details



20-733, TPF-5(438)








Smart Work Zone Deployment Initiative

Principal Investigator
Timothy Gates
Co-Principal Investigator
Peter Savolainen

About the research

Work zones that include a single lane closure on a two-lane, two-way roadway present unique traffic control challenges. In these situations, traffic regulators (i.e., flaggers or temporary traffic signals) are often utilized to regulate traffic such that only a single direction utilizes the open travel lane at any time. Recently, an experimental traffic control treatment, referred to as the driveway assistance device (DAD), was developed to 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 along with a steady red indication. As the DAD is a relatively new and under-researched treatment, much is still unknown about the optimal designs of the signal display and auxiliary signage to provide the highest comprehension and compliance.

To address these issues, research was performed to determine best practices related to the DAD design and to develop guidelines related to the use of DADs in one-lane, bi-directional work zones. First, a nationwide online survey of drivers was conducted to determine the DAD signal configurations and auxiliary sign messages that elicited the highest rates of compliance or most effectively communicated the proper driver action. The survey was supplemented by a field study performed in northern Michigan that evaluated the effects of five different auxiliary signs on driver compliance when utilized with a DAD. The conclusions and recommendations resulting from these efforts are summarized as follows. The auxiliary signs most effectively conveyed the proper driver action if the message included the word “Turn” as opposed to “Yield” and if a No Turn on Red Sign was included. Additional improvements were observed for signs that included a prominent “WAIT” message at the top of the sign. These findings were consistent between the survey and field study. Turning to the characteristics of the DAD signal indication, compared to yellow flashing arrows, red flashing arrows showed far fewer “Turn at any time” survey responses, although yellow flashing arrows showed considerably less uncertainty as to the proper action for drivers. Considering the DAD signal head configuration, the horizontal and doghouse configurations more effectively conveyed the proper driver action compared to the red-over-yellow arrows configuration in the driver survey. Based on the research findings, DADs are recommended for continued experimental use along with appropriate auxiliary signage at work zones that include one-lane, two-way traffic where it is not practical or feasible to provide a continuous flagger or temporary traffic signal operation.