Mobile Surveillance & Wireless Communication Systems Field Operation Test

Problem

Traffic monitoring can be difficult in areas where permanent detectors, electrical power, and communications systems are not available. This research sought to evaluate the performance of wireless traffic detection and communications systems

Method

The researchers designed and built six surveillance and three ramp meter trailers, a video and data retransmission (or relay) site, and video and data reception facilities at the Caltrans District 12 and Anaheim Traffic Management Center (TMCs) and the University of California at Irvine Institute of Transportation Studies Laboratory. The system was evaluated in two different types of tests. The Anaheim Special Event Test assessed the surveillance trailers in an application that transmitted video imagery in support of arterial traffic control during a special event. The Interstate-5 (I-5) Test examined the use of the mobile surveillance and ramp meter trailers to transmit video imagery and data in support of freeway ramp metering.

Findings

Several difficulties were encountered with the trailers. These include:

• Frequent discharge of electrical systems. This was remedied with a complete redesign of the generator, battery, charging, and power architecture systems.
• Difficult logistics and setup with the use of the trailers. Several weeks and multiple personnel were required to select sites, perform signal strength testing, secure permits, and determine the best way to position the trailers. Moving a trailer a few kilometers and deploying it took about an hour. On construction sites, contractors need to be made aware of the surveillance trailers' use so that space can be allocated for them and thereby reduce the need for the trailers to be repositioned. Supplemental relay sites would also reduce logistics problems.
• Strong winds occasionally moved antennae off mark.

The video system used tended to over-report mainline volume. This is due in part to the maximum height at which the video detectors can be mounted on the portable trailers. In particular, tall vehicles tended to be counted as multiple vehicles; tall vehicles also tended to obscure smaller vehicles and cause them to be underreported. A method of compensating for vehicle overcount by the system studied is needed in order to report more accurate traffic volumes.

The ramp signals responded properly to vehicle demand an average of 85 percent of the time. This is not adequate for ramp-metering operation. Positioning the video camera closer to the ramp may reduce this error. Increasing the camera's field of view and using optical recognition logic may further reduce the error.

Fuel (LPG) consumption of a surveillance trailer was estimated at 0.46 gallons/hour. With an LPG cost of $1.75/gallon, fuel for continuous surveillance trailer operation is estimated at $0.80/hr.