Speed Study in Oregon Reveals Lessons Learned towards Safer Traffic in and around Work Zones.
Oregon, United States
Speed Variation and Safety in Work Zones
Summary Information
The difference between vehicle speed and the average speed on the roadway has been identified as an important contributing factor to roadway crashes, especially in work zones. This study developed knowledge and practices that can be used to improve driver and worker safety (and as a result, mobility) in work zones. This study focused on select work zones in Oregon that featured high-speed roadways and typical mobile construction and maintenance operations, such as paving and restriping. The study, in coordination with ODOT staff, examined the effectiveness of four interventions for minimizing and mitigating variation in vehicle speed at work zones through field testing on three case study projects.
The four interventions field tested included:
- A “pace car” continuously traveling at or slightly below the posted speed limit throughout the work zone
- A portable changeable message sign (PCMS) with custom messages placed at the advance warning area in the work zone,
- The combination of a pace car and a PCMS
- The combination of a PCMS unit and flashing amber/white lights on paving equipment that were operating in the active work area.
Periods of testing were conducted during the summers of 2019 and 2020 for comparison, both without the traffic control intervention (control) and with the selected interventions. Portable traffic sensors were deployed at multiple locations throughout the planned work area to record vehicle speeds. The data were downloaded and analyzed with statistical methods.
- Use a combination of portable changeable message signs (PCMSs) and flashing amber/white lights as traffic control treatments to reduce speed and speed variation in work zones. A PCMS showing custom messages such as “MAINTAIN CONSTANT SPEED / THRU WORKZONE” could be placed at the advance warning area in the work zone. The results showed that intervention (1) with the pace car did not show any significant effect but intervention (2) with the presence of PCMS was effective at reducing speed variation in the work zone, especially for locations closer to the construction workers and equipment. Compared to the control case, the reductions in one-min standard deviations (SD) in vehicle speeds ranged from 1.29 mph to 2.05 MPH; the reductions in 5-min SD ranged from 0.76 miles per hour (mph) to 2.52 mph.
- Have a “pace car” continuously travel at or slightly below the posted speed limit throughout the work zone in combination with a PCMS. This could serve as a promising speed variation intervention. The results of this study showed that while intervention (1) alone did not show any significant effect, intervention (2) where the combination of the PCMS and pace car was used, was more effective in reducing speed variation than any single treatment alone in the active work area.
- Be strategic about the placement of the PCMS. The PCMS should ideally be placed at the midpoint between the “roadwork ahead” sign location and the beginning of the taper location. One of the field experiments in this study showed that placing the PCMS unit close to the “roadwork ahead” sign at the beginning of the advance warning area could be ineffective in reducing speed variation in the downstream work area because drivers who enter the work zone through freeway entrances downstream of the RWA sign would not see the message on the PCMS.
- Determine the number of PCMS based on work zone characteristics. Depending on the length of the work zone and the number of roadway entrances and exits throughout the work zone, it is recommended to place one or more PCMS units in the advance warning area and at the transition area to remind drivers to travel at a constant speed relative to surrounding vehicles to reduce speed variability.
- Incorporate work zone accident data into analysis to better back up findings. This would enable DOTs or researchers to establish a direct relationship between speed variation and crash occurrence in work zones.
