This study evaluated a queue warning system (QWS) installed throughout the construction work zone (between mile markers 161 and 181) on U.S. Highway I-25. The QWS was evaluated during September and December 2019 for how well it mitigated sudden vehicle or traffic stops. The average vehicle speed and the average speed reduction during the system activation period were used as measures of effectiveness (MOEs).
The following summarizes the lessons learned from the effectiveness analysis, and from installation, maintenance, and data verification.
- Emphasize placement of the sensors and message boards, aiming of the sensors, visibility of the message boards and the sensitivity of the device detection. Aim the sensors to enhance traffic detection and to ensure that construction activity does not interfere with detection.
- Display “Slow Traffic Ahead” and “Stopped Traffic Ahead” messages to increase travel speeds, reduce speed reduction occurrences, and facilitate traffic movement. The analysis indicated that average speeds were higher and there were fewer abrupt speed reductions during activation of the QWS “Slow Traffic Ahead…” and “Stopped Traffic Ahead…” messages.
- Conduct visual inspections in the field, data verification, field adjustments, and verification of the field adjustment on at least a weekly basis to ensure that the QWS was set up and operating as intended throughout the life of the project.
- Visual inspection should include a review of the placement of sensors and message boards. Sensors should be placed at distances close to the desired set up and all message boards should be placed to ensure proper line-of-sight to oncoming travelers.
- Data collected by the devices should be downloaded and reviewed for completeness and to identify if and when system devices are not measuring filed data properly.
- If necessary, contact the vendor to make field adjustments. Perform visual inspections and data review to verify that field adjustments were made successfully. Repeat the entire process if necessary.
- Improve the reliability of QWS devices by regularly inspecting and reviewing detection data and enforcing penalties for failure to do so. CDOT's use of a pay reduction penalty was effective in significantly improving the reliability of the devices.