Iowa Field Test Study Showed a Combination of Dynamic Message Signs and Fixed Signs Reduced Tailgating by 29 Percent in a Construction Zone.
Study Implemented Different Configurations of DMS Locations and Messages to Measure the Impact of Car Following Distance on Work Zones.
Cedar Rapids, Iowa, United States
Evaluation of Messaging Techniques to Increase Vehicle Spacing at Work Zones
Summary Information
Work zones significantly disrupt standard traffic flow. This disruption can increase collision risks, particularly rear-end crashes. The 2014 Federal Highway Administration' statistics highlighted that over half of all work zone crashes were rear-end collisions, frequently caused by tailgating and speeding. These behaviors reduce drivers' reaction time, especially in work zones where traffic conditions unpredictably change. Addressing tailgating in these locations is crucial, requiring research into effective strategies to mitigate its risks and maintain safety. The objective of this study was to
- conduct a message design and comprehension test involving the development of graphics and messages tailored for both fixed signs and dynamic message signs (DMS), and;
- evaluate the effectiveness of the design in real-world settings.
METHODOLOGY
This study began by creating many different styles of warning messages designed to increase driver gap acceptance in work zones. It experimented with messages that were numerical versus general, text based versus graphical, and positive or negative. It then administered surveys to 247 respondents (including 44 from the Ames DMV and 203 from the Ankeny DMV) across several different days to gauge driver reaction and comprehension. Messages which were scored high enough across each metric were then tested in actual work zones. Field tests were conducted at two construction sites: a single-lane closure site on US 30 and a shoulder closure site on I-80.
The first test was classified into four experimental periods:
- Baseline. August 21 through September 10, 2022 (3 weeks)
- Only Overhead DMS. September 11 through September 24, 2022 (2 weeks)
- Overhead DMS and Fixed Signs. September 25 through October 8, 2022 (2 weeks)
- Only Fixed Signs. October 9 through October 19, 2022 (10 days)
The second field test was divided into three periods:
- Baseline. May 16 through June 18, 2023 (5 weeks)
- Only portable DMS. June 19 through July 11, 2023 (4 weeks)
- Portable DMS and Fixed Signs. July 12 through August 18, 2023 (5.5 weeks)
Radar detectors were used to capture speed and flow data. To fully understand driver behaviors related to tailgating, sensors were installed both upstream of the construction zones and directly within the active work zones. The two key performance metrics were the mean headway (in seconds) and the probability of tailgating occurrences. The mean headway was calculated from the average of all headways under five seconds where speeds exceeded 45 mph. The probability of tailgating occurrences was determined by the proportion of severe tailgating instances (with a headway of one second or less and speeds greater than 45 mph) relative to the hourly traffic count.
FINDINGS
- In the first field test of a single-lane closure on US 30 with the combination of fixed sign and DMS, the tailgating occurrence percentage decreased from 14.12 during the baseline to 10.08, a 29 percent reduction.
- In the second field test, when fixed signs were added, there was an increase of about 0.1 seconds in average headway and a slight drop in the probability of tailgating occurrences between the upstream and work zone areas.
- Signs that were phrased positively but not humorously, did not contain numbers, and were structured with the warning after a question received the highest receptivity and clarity scores.
