8 Work Zone Safety
8.3 Safety Radar
8.3.1 Work Zone Safety Warning System – Iowa and Kansas
The information on the Safety Warning System was obtained from the Midwest States Smart Work Zone Deployment Initiative Year One Report.22
Impetus for the Activity
The States of Iowa, Kansas, Missouri and Nebraska formed the Midwest States Smart Work Zone Deployment Initiative to test and evaluate technologies for improving safety and efficiency of traffic operations in work zones. By working together, the agencies avoid unnecessary duplication of research through sharing of research results.
Criteria for System Selection (Hardware and Software)
The group held a series of three workshops to identify work zone problems, to define solutions and to select the technologies for evaluation. Potential solutions were presented by technology providers, and these solutions were matched with work zones on specific construction projects. The Safety Warning System, provided by MPH Industries, Inc. was matched with work zones in Iowa and Kansas.
Description of the System
The purpose of the system is to send warning messages concerning road hazards to drivers with vehicles equipped with either Safety Warning System detectors or K-band radar detectors. Simple K-band radar detectors will sound a basic alarm. Radar detectors capable of reading Safety Warning System messages display the specific message to the driver, such as, “Left Lane Closed Ahead.” The detector can identify and display over 60 messages under 5 categories. The 5 categories include:
- Highway construction/maintenance;
- Highway hazard zone advisory;
- Weather related hazards;
- Travel information/convenience; and
- Fast/slow moving vehicles.
Thus, this technology may have applications in rural safety outside of work zones.
The Safety Warning System was deployed and tested in Iowa in September 1999. The transmitter was deployed in a rural work zone on I-35 that involved a left lane closure leading to a median crossover. The purpose of the deployment and test was to evaluate the impact of the system on reducing speeds in work zones. The system consisted of one transmitter, which was mounted on a stationary pole (it can also be mounted on a vehicle) 685 m upstream of the taper.
The Kansas deployment and test was performed on a rural work zone on I-135 that also involved a lane closure leading to a median crossover. The purpose of the deployment was to provide advance warning to vehicles.
The system does not collect any information on current conditions, it simply transmits the set advisory messages to in-vehicle radar detectors.
System Performance
No problems with system performance in the Iowa deployment were mentioned in the report.
System Effectiveness Evaluation
The system was formally evaluated in both Iowa and Kansas.
In Iowa, traffic data was recorded two days prior to and two days after the Safety Warning System Transmitter was installed. Data was collected 457 m and 152 m upstream of the taper using two traffic data collection trailers.
The evaluation parameters included:
- The time mean speed;
- The speed that 85% of the vehicles travel;
- The 16 km/h speed interval containing the most observations;
- The percentage of observations in the 16 km/h pace;
- The standard deviation of the time speed;
- The percentage of observations complying with posted regulatory and advisory speed limits; and,
- The time mean speed of the highest 15% of speeds.
No statistically significant differences were found in the speeds when the transmitter was in place. There was however, in all data sets, a slight increase in the number of vehicles observing the speed limit while the system was deployed. There were no discernable trends in the other evaluation parameters.
Project personnel felt that speeds probably did not differ significantly before and after deployment due to the small number of vehicles equipped with radar detectors that are capable of receiving the Safety Warning System messages. They did, however, feel that the system holds promise as a means of warning drivers of upcoming hazardous conditions, but noted that the number of radar detector users will have to increase for the system to be effective in reducing speeds.
In Kansas, data was collected for one 24-hour day before system installation and one 24-hour day after. Lane distribution upstream of the project, vehicle speeds upstream of the project and vehicle speeds in the crossover were used as the performance measures. Data were collected using pneumatic tubes and automatic traffic recorders 152 m, 305 m and 457 m upstream of the taper.
After installation, small reductions (less than 1.6 km/h) in the mean and 85th percentile speeds were observed in the crossover for passenger cars at night and for both cars and trucks during the day. There were a number of statistically significant results related to the percent of drivers exceeding the speed limit. For passenger cars, the percent of drivers exceeding the speed limit decreased by more than 20% for day and night. For trucks a significant reduction of 16% was observed during the day. A small reduction of 8% was observed at night, but it was not significant. The difference between cars and trucks was expected because most system compatible devices are radar detectors, which are illegal in commercial vehicles. No statistically significant changes in lane distribution were observed.
Project personnel concluded that, based on the results, the system can’t be recommended on the basis of speed reduction alone. However, they did note that the device may have the potential to improve work zone safety by alerting drivers that unusual roadway conditions/hazards require attention.
Obstacles and Lessons Learned
It appears that the major obstacle encountered was the lack of in-vehicle system compatible radar detectors in the vehicles passing through the work zones.