Use Driveway Assistance Devices in Work Zones
BY AsphaltPro Staff
Editor’s Note: This summary of 115893 ODOT Final Report (3/2023) offers an overview of researchers’ findings on the use of driveway assistance devices (DADs) in an Ohio rural project. Please use this to pique your interest and then dive into the full report for detailed information at https://rb.gy/vj3eu.
In 2022, the Ohio Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration, worked with ODOT District 5, its Central Office, and Shelly & Sands specifically to collect data and evaluate temporary traffic signals and driveway assistance devices in work zones. The team worked within the ODOT construction contract 210208, which was awarded to Shelly & Sands, on State Route 60 (SR60), in Muskingum County.
According to the report “Evaluation of Driveway Assistance Devices in Signalized Work Zones,” prepared by Deborah S. McAvoy, Ph.D., P.E., PTOE, Bhaven Naik, Ph.D., P.E., PTOE, and Jean Hartline, P.E. PTOE, researchers “examined the performance differences between traditional temporary traffic signals and Driver Assistance Devices (DADs) at driveways in a work zone. The project consisted of a field and microsimulation analysis to quantify operational and safety of both work zone driveway devices, a benefit-to-cost analysis and a user survey.”
The results of their work “indicate that the DADs provide higher levels of driver compliance, improved operational performance and reduced the potential for crashes through work zones over the traditional temporary traffic signal devices.”
The abstract suggested that roadway users understood how the DADs operated and that “construction personnel preferred the DADs over the temporary traffic control signal devices for construction operations and safety reasons.”
Let’s take a closer look at the ODOT study of DADs in work zones.
Temporary Compliance
In its problem statement, the report acknowledges that work zones along major thoroughfares can separate traffic flow with rigid barriers, but when it comes to two-lane roadways, workers are at a disadvantage. The authors remind readers that these setups typically involve temporary traffic signal devices to allow for alternating traffic flow using partial-width construction methods for the roadway, stating this “is particularly common along suburban and rural two-lane roadways.”
The authors zero in on the use of DADs for two-lane roadways.
“When a part-width work zone requires one-way travel along a two-way corridor, driveways and low volume intersecting roads within the work zone create additional challenges.” One of those challenges is how to let drivers enter the mainline one-way traffic stream safely from a driveway in the middle of the work zone. Researchers offer the DADs as a method to:
- safely control driveway traffic within single-lane operation work zones with two-way traffic;
- improve operations by allowing motorists at driveways (and potentially for low volume intersecting roads) to join an existing queue of vehicles;
- reduce user delay;
- increase safety; and
- improve construction efficiency (if one-way work zones can be expanded).
This driveway assistance device (DAD) is from Superior Traffic Services.
At the time of publication, DADs had been developed to safely control driveway traffic within single-lane operation work zones with two-way traffic but had not received approval for inclusion in the FHWA’s Manual on Uniform Traffic Control Devices (MUTCD). The researchers and report authors hoped to determine the feasibility for future use of DADs; if they proved a safe, efficient, and effective temporary traffic control device, inclusion in the MUTCD would allow for widespread use.
SR60 for Control
SR60 is a two-lane, two-way roadway, with a posted speed limit of 55 miles per hour. It’s reported to have an average daily traffic of 3,800 with 13% heavy vehicles. The full depth replacement ODOT project was about 8 miles in length and included widening, bridge rehab and box culvert replacement, according to the report.
An excerpt from the report describes the work zone layout in detail:
“The work zone configurations included the closure of one of two of the travel lanes for approximately 1,000 feet in length while construction was occurring on the other lane. During construction, access to the driveways was maintained by either a temporary traffic signal or the DAD. Traffic was controlled at both ends of the work zones with a temporary traffic signal. The specific study area included four work zones, three utilizing DADs at driveway locations and one utilizing temporary traffic signal devices at driveway locations. All of the work zones utilized temporary traffic signal devices at the end of each work zone.”
To compare performance of the DADs against traditional temporary traffic signals, the researchers collected volume, queuing, compliance, safety and speed of vehicles within the work zone, both along the mainline as well as at the driveways. They also administered survey questionnaires to determine public and worker perception of the traffic control devices. They conducted microsimulation-based analyses to compare operational performance of the temporary traffic signals and the DADs. (They also conducted a sensitivity analysis using microsimulation to determine appropriate deployment metrics for the DADs.) And they conducted a cost-to-benefit analysis to determine the efficacy of using the DADs in the future for partial-width construction using one-lane, one-way traffic.
The data collected at the driveway locations included the following information:
- Camera information (i.e., driveway location and name)
- Data collection timeframe (i.e., day and time)
- Direction of travel (i.e., mainline and driveway)
- Platoon description of the mainline vehicles (i.e., platoon or random arrivals)
- Number of mainline vehicles not a platoon (i.e., including straggler vehicles)
- Time of the front of middle platoon vehicle and end of vehicle passing a specified location
- Time of arrival and departure of a driveway vehicle
- Driveway queue length
- Notes on any conflict of the driveway motorists with the mainline vehicular traffic
- Turn compliance (i.e., whether the driver complied with the device)
- Turn relation to the mainline adjacent vehicle (i.e., within 150-feet or less)
- Turn direction (i.e., with or against the mainline traffic flow)
The data collected at the end of the work zones included the following information:
- Camera information (i.e., driveway location and name)
- Data collection timeframe (i.e., day and time)
- Direction of mainline travel
- End of the work zone queue length at the start of the green signal indication
In the surveys that were conducted, the report showed more than 60% of respondents understood the movements that were allowed under the DADs signal configuration.
Researchers also administered surveys to individuals involved in the construction of the SR60 project. “The purpose of this was to determine how people involved in highway construction project perceived the relationship between temporary traffic control devices, highway safety in work zones, and construction productivity when comparing the DAD devices to temporary traffic signal devices. The respondents included 30.77% ODOT employees, 23.08% consultants, and 46.16% construction personnel.”
Those responses from the “construction-related” survey showed 92.31% of the respondents felt that the driveways controlled with DADs provided an improved rate of construction productivity. More data is summarized in the full report, available at https://rb.gy/vj3eu.
Researchers found the DADs offered multiple benefits during the SR60 project. One area in which the DADs performed well was in reducing delays at driveways while slowing vehicle speeds through the work zone itself. In other words, drivers complied with the devices, allowing the devices to serve their purpose.
The report lists the following in that regard:
- DADs yielded statistically shorter delays at driveways and shorter queue lengths along the mainline roadway at the end of the work zone.
- DADs yielded statistically slower vehicular speeds through the work zone.
- DADs yielded statistically higher levels of driver compliance.
- The placement of DADs in the work zone does not impact driver compliance.
Readers will find additional results of data gathered, surveys conducted, benefit-to-cost calculations, microsimulation analyses and statistical analysis results in the report. The appendices include the specific questions asked in the surveys as well as existing literature describing how Texas DOT, the Texas Transportation Institute, New Jersey DOT, Michigan DOT, Michigan State University and others have employed DADs and hybrid devices to solve traffic and work zone issues in the past decade.