Dynamic Speed Feedback Signs and Speed Wizard Application Reduced Work Zone Speeds by More Than Five Percent and Cut Severe Speeding Violations by At Least Eight Percent.
A Field Study on I-65 Work Zone Compared Vehicle Trajectories Across Three Speed Management Strategies.
Robertson County, Tennessee
Strategies for Improved Driver Behavior within Work Zones
Summary Information
Speeding within freeway work zones poses safety risk to both workers and motorists. Although traditional enforcement measures such as police patrols can help manage speeding, continuous enforcement in work zones is often impractical, labor-intensive, or cost-prohibitive. This study evaluated driver speed behavior and compliance on a freeway work zone under three different speed management strategies: 1) Dynamic Speed Feedback Signs (DSFS), 2) Speed Wizard (SW), and 3) combinations of Speed Wizard with Portable Changeable Message Signs (PCMS). The field evaluation was conducted in 2023 on I-65 southbound in Robertson County, Tennessee, over approximately two and a half months.
METHODOLOGY
Vehicle trajectory data were extracted from high-resolution video collected by five solar-powered cameras placed along the corridor. Following the video data processing using object detection and multi-object tracking methods, 22,950 individual vehicle trajectories were obtained, classified by lane, vehicle type, feedback condition, and environmental context. Four scenarios were used in the analyses: (i) Base (no feedback), (ii) DSFS, (iii) SW, and (iv) Combined (SW and PCMS).
Statistical models were used to examine factors associated with speeding severity, including moderate speeding of 10 to 15 MPH over the limit and severe speeding of more than 15 MPH over the limit and capture non-linear speed changes along the corridor. Spatial analysis was also used to measure how vehicle speeds were influenced by nearby vehicles and spatial traffic interactions.
FINDINGS
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The study found that speed feedback systems reduced speeding behavior along the I-65 freeway work zone. DSFS and SW showed stronger effects than the combined (SW + PCMS) treatment. The largest mean speed reduction for SW was 2.97 MPH, followed by DSFS with 2.06 MPH and the combined treatment with 0.74 MPH. Overall, multiple speed-feedback messages reduced effectiveness, suggesting that simpler, more focused driver feedback may outperform layered messaging.
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Moderate speeding violations and severe speeding violations were reduced by at least eight percent under feedback sign deployment. Vehicle speed was also reduced by more than five percent in each feedback sign deployment.
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Despite the posted work zone speed limit of 55 MPH, it was found that about 75 percent of vehicles traveled above the posted speed limit. After passing the feedback sign, vehicle speeds tended to stabilize around 58 MPH; vehicles traveling above this threshold tended to decelerate, while slower vehicles tended to accelerate.
The spatial analysis showed that the benefits of feedback signs extended beyond individual drivers. Vehicle speeds were spatially correlated, meaning drivers adjusted their speeds partly in response to nearby vehicles. For example, DSFS had both a direct speed-reduction effect on exposed drivers and an indirect spillover effect on surrounding vehicles, with a combined reduction of more than 5 MPH.
