InTrans / May 16, 2022

Research studies driveway assistance devices (DADs) as potential work zone option

An example of a DAD

Whether it’s a rural driveway with a single vehicle entering or leaving the house or a busy fast-food chain with near-constant traffic, these access points can be difficult to work around during a construction project.

The low-volumes or the locations can make it impossible to staff a flagger around the clock or place a portable traffic signal. However, a recent innovation known as a driveway assistance device, or DAD, could be a solution.

DADs are wirelessly connected with temporary traffic signals, which may be in a variety of configurations and typically with some additional signage, placed at each end of the lane closure and are coordinated with the signal timing plan for directional traffic on the major roadway.

It is important to note that DADs have not been adopted into the MUTCD and are considered an experimental traffic control treatment. However, as of late 2021, 8 states have received permission from the FHWA to experiment with the DAD; an additional 13 states—including Iowa—have permitted the use of DADs on specific projects, and 5 other states have expressed interest in the DAD.

A recent research project produced by the Smart Work Zone Deployment Initiative (SWZDI) led by Michigan State University Professor Timothy Gates conducted a nationwide survey and subsequent field evaluation in Michigan related to the use of DADs in work zones to help determine the best practices for their design and develop guidelines for their deployment.

Key findings from the research project include the following:

  • Use of a DAD generally resulted in a high proportion of safe movements during the field study, with an overall safe movement rate of nearly 93 percent
  • The principal findings related to DAD auxiliary signage from both the survey and field study are as follows:
    • Auxiliary signs that included the word “Turn” more effectively conveyed the proper driver action compared to “Yield”
    • Additional improvements were observed for signs that included a prominent “WAIT” message at the top of the sign
    • The inclusion of a No Turn on Red (NTOR) sign strengthened the message effectiveness and increased the response rate to the circular red indication
  • Additional survey results related to the DAD signal characteristics are as follows:
    • Red flashing arrows elicited far fewer of the incorrect “Turn at any time” survey responses compared to yellow flashing arrows
    • However, yellow flashing arrows showed considerably less uncertainty as to the proper driver action compared to red flashing arrows
    • Horizontal and doghouse signal-head configurations more effectively conveyed the proper driver action compared to red-over-yellow arrows

The project also included implementation recommendations for those agencies that get approval to use the experimental device. The ultimate aim of the project was to provide further support for interim approval and subsequent adoption of DADs into a future version of the MUTCD.

“The research indicates a DAD could be a potentially low-cost and promising alternative to flaggers or other types of traffic regulators at low-volume access points, providing potential cost savings, productivity benefits, and increased worker safety. This is especially the case if proper auxiliary signage is utilized along with the DAD,” said Gates.

The full research report and a technical summary are available at this research page and an Iowa LTAP webinar on DADs is available here.