Smart Traffic Sign Assisting Flagger Control in Work Zones in Minnesota Was Tested Through Driver Simulations and Field Pilot in Terms of Driver Compliance.
Scott County
User-Centered Smart Traffic Sign Development Study
Summary Information
Work zone flaggers protect workers by providing temporary traffic control and maintaining a safe traffic flow. However, their safety could be at risk from vehicles intruding into work zones. This project developed a smart traffic sign using low-cost radar chip-based vehicle tracking sensors that can automatically detect potential intruding vehicles and provide an audio-visual alert to warn both the driver and workers in the work zone of the impending event. Usability testing of the initial prototype of the smart traffic sign was conducted in a driving simulation environment involving 36 participants in July 2022, simulating work zones on Scott County Highway 81 in Spring Lake Township, Minnesota. Based on the feedback from the participants in the first round of testing, a second round of tests was conducted with 20 participants, simulating the same driving scenarios, where the signage (flagger and experimental traffic signal) was modified to improve driver performance and response. In addition, the study developed and demonstrated the capabilities of the prototype sensing system that could track the trajectories of nearby vehicles both in real traffic and in controlled simulation tests.
METHODOLOGY
The effectiveness of the developed smart traffic signal was tested and compared with the traditional flagger operations using a driving simulator with two separate work zones. In the control scenario the flagger rotated the sign to the “STOP” side, signaling the driver to stop and hold this position for one minute before flipping the sign back to show “SLOW”. In the treatment scenario, the light first turns to solid yellow then to solid red signaling the participant to stop. The light changes to flashing yellow after one minute, signaling the participant to proceed.
In the second round of the driving simulator scenarios, flagger operation and the smart traffic signal were modified based on the feedback from the first round’s participants. Two modifications were made to the flagger operations: (i) drivers were alerted via audible and visual warnings (ii) flashing red LED lights were installed around the STOP sign. Three modifications were made to the smart traffic sign: (i) “Stop Here on Red” sign was installed at the signal post, (ii) a worker was placed by the signal, (iii) a reflective yellow border was added to the sign to improve visibility.
For the field experiments, 24 vehicle runs were measured during the testing of the intrusion detection system. The runs included 11 vehicles staged to intrude the test area and 13 staged to safely stop or to quickly approach but to stop before intruding.
FINDINGS
- In the first round of the tests, drivers violated the signal light 39 percent of the time compared to 18 percent overall violations with the flagger. Moreover, 93 percent of the signal violations were observed among participants who experienced the signal in their first drive compared to the drivers that experienced the flagger in their first drive.
- When testing the modified systems in the second round of the tests, drivers violated the flagger 15 percent of the time, and the signal 40 percent of the time. In addition, 87.5 percent of the violations of the modified traffic signal occurred among the group that experienced the traffic signal in their first drive.
- The results of the usability testing of the prototype smart traffic signal developed and fabricated in this study revealed that, while 22.8 percent of drivers with the traditional flagger without the alarm system stopped but did not remain stopped, only 10 percent of drivers presented with the alert flagger system committed the same failure, suggesting 14 percent points reduction in failure to comply.
- In the field experiments, 24 vehicle runs were measured during the testing session, and all intruding vehicles were correctly detected.
