3 Speed Management
3.2 Variable Speed Limits
3.2.1 New Jersey Turnpike Variable Speed Limit System
Impetus for the Activity
The New Jersey Turnpike Authority considered a technological treatment to ensure an effective traffic management system that provides motorists with a safe and efficient roadway. A technological treatment was chosen over a more conventional treatment to take advantage of available technology to improve traffic control, as well as provide significant improvements in roadway operations.
The expected result of installing the system was to increase the safety and comfort of motorists, as well as to improve roadway operations.
Criteria for System Selection (Hardware and Software)
The Turnpike Authority selected the system that it did based on staff and consultant recommendations.
Description of the System
The system was installed in the early 1960s and is currently active. The purpose of the system is to provide early warning to motorists of slow traffic or hazardous road conditions.
The system is located on the New Jersey Turnpike – an Urban/Rural freeway/high-speed limited access roadway. The system has approximately 120 signs over 238 km and uses inductive loop detectors to collect speed and volume data. The addition of weather-sensing equipment is planned in the near future.
The posted speed limits are based on average travel speeds and are displayed automatically (manual override is used for lane closures and construction zones). The posted speed limit can be reduced from the normal speed limit (105 km/h, 89 km/h, or 80 km/h depending on the milepost location) in 8-km/h increments, to 48 km/h. The posted speed limit can be reduced for six reasons: crashes, congestion, construction, ice, snow, and fog.
System output includes posted speed and warning by means of Speed Limit/Speed Warning signs (CMS and VMSs). The speed warning signs display, “Reduce Speed Ahead” and the reason for the speed reduction. When appropriate, the distance between the warning sign and the beginning of the congestion is displayed on the warning sign. The system updates every minute. The posted speeds are enforced.
System Performance
Although system performance has not been formally tested, in the opinion of the Turnpike Authority, the system has performed satisfactorily. System performance is monitored by in-house testing to identify any technical problems, operable and inoperable equipment, and maintenance that is evaluated daily. The New Jersey Turnpike Authority operations department personnel monitor the system 24-hours per day, 7 days a week.
System Effectiveness Evaluation
Based on observation and experience, the New Jersey Turnpike Authority feels that the signs are effective. The signs provide motorists with information on unusual roadway conditions, which dictate the need for speed reduction. State Police enforce the reduced speed limits by issuing summonses to those motorists found to be in violation.
Obstacles and Lessons Learned
The ever-changing technology that resulted in continuously and constantly updating and upgrading the system was noted as an obstacle.
Additional Comments
The Speed Limit/Speed Warning and CMSs are a part of the New Jersey Turnpike’s Automatic Traffic Surveillance and Control System (ATSCS). Their function is to alert motorists of any incidents detected by ATSCS, which have occurred on the roadway.
Incident information is transmitted electronically, via loop detectors in the pavement, to the Authority’s Operations Command Center where the sign information is generated and displayed instantaneously to the Speed Limit/Speed Warning message boards, alerting motorists of hazardous roadway conditions.
ATSCS detects incidents and minimizes congestion and delays via information displayed on the Speed Limit/Speed Warning overhead signs. This system maximizes the use of available roadway capacity and ensures the safety of motorists.