Field Study Using Speed Trailer With Red and Blue Lights Resulted in Over 50 Percent Speed Reduction in a Work Zone in the St. Louis Region During Daytime and Nighttime.

Researchers Assessed Effectiveness of Various Speed Management Countermeasures Including Speed Display Trailer, Work Vehicle With Red and Blue Lights, and Active And Passive Law Enforcement in Missouri.

Date Posted
03/31/2023
Identifier
2023-B01733
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Effectiveness of Speed Management Methods in Work Zones

Summary Information

Speed management is considered a viable strategy to reduce work zone crashes. In this study, field study, simulator study, and driver survey were conducted to investigate the effectiveness of speed management countermeasures, including speed display trailer, speed display trailer with red and blue lights, speed trailer with flashing speed, work vehicle with red and blue lights, and active and passive law enforcement, in managing vehicle speeds in work zones. The field study was conducted at a work zone on I-270 in the St. Louis region in August 2021. 

METHODOLOGY

A field study was conducted to collect and analyze approximately four weeks of data from a work zone on I-270 westbound, spanning from the Lindbergh Boulevard interchange to Dunn Road during August 3-26, 2021. The data collection setup for the field study involved two radar sensors mounted on portable trailers, one upstream and the other downstream from the work zone speed countermeasure location. Various countermeasures, including the following were deployed in the work zone during both daytime (6 a.m. to 6 p.m.) and nighttime (6 p.m. to 6 a.m.) during the four-week period:

  • No treatment or countermeasures (base), 
  • Speed trailer, 
  • Speed trailer with flashing speed when vehicles are speeding, 
  • Speed trailer with red and blue lights (red and blue lights flashing when above speed limit), 
  • Passive law enforcement (only police vehicle stationed on the shoulder)
  • Active law enforcement (police officers actively pulling violators in addition to a police vehicle stationed along the roadside), and 
  • Work vehicle with flashing red and blue lights (nighttime only). 

FINDINGS

Daytime Results

  • Field study results showed that the use of speed trailer with flashing speed feedback during daytime led to an additional speed reduction of 1.3 miles per hour (mph), equaling a 24.8 percent further speed reduction compared to the base scenario.
  • During the daytime, the speed trailer with red and blue lights was associated with an additional speed reduction of 2.8 mph, meaning a 53.5 percent further speed reduction compared to the base scenario.
  • Although the speed trailer without red and blue lights was not as effective in reducing vehicle speeds as the other scenarios, it still resulted in an additional speed reduction of 0.5 mph, translating into a 9.9 percent further speed reduction compared to the base scenario.
  • During daytime hours, the implementation of active law enforcement resulted in a 4.3 mph decrease in speed, indicating an 81.7 percent additional speed reduction compared to the base scenario.
  • Similarly, during daytime hours, the implementation of passive law enforcement resulted in a 2.4 mph decrease in speed, equating to a 46 percent additional speed reduction compared to the base scenario.

Nighttime Results

  • In the nighttime scenario, utilizing a speed trailer with a speed display resulted in an additional speed reduction of 0.9 mph, translating to a 22.9 percent further decrease in speed relative to the base scenario.
  • Implementing a work vehicle equipped with red and blue lights yielded an additional decrease of 2.1 mph, corresponding to a 51.9 percent further reduction in speed compared to the base case.
  • The use of active law enforcement during nighttime hours was correlated with an additional speed reduction of 5.5 mph relative to the base scenario, signifying a 135.8 percent further decrease in speed.
  • During nighttime, passive law enforcement was the second most effective countermeasure with an additional speed reduction of 2.8 mph compared to the base scenario, which meant a 69.7 percent further reduction in speeds. 

Figure 1. Speed display trailer deployed in work zone on I-270 near Saint Louis, Missouri (Source: MoDOT)

Figure 2. Work vehicle with flashing red and blue lights in work zone during nighttime road work on I-270 near Saint Louis, Missouri (Source: MoDOT)

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