Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Additional Description of Strategies
Information Collection and Dissemination
2.1. Surveillance and Detection
A variety of surveillance and detection technologies are able to detect incidents quickly. These
include inductive loops, acoustic and microwave vehicle detectors, and camera systems that
provide frequent still images or full-motion video. These ITS technologies help incident
management personnel identify incidents shortly after they happen. Surveillance and detection
solutions along a corridor or within a region can provide considerable long-term benefits and are
critical elements for establishing a nationally available, real-time traffic and travel conditions
monitoring system (9).
Additionally, reducing annual road accidents and deaths requires more than improved vehicle and
roadway technologies. Surveillance treatments also include evaluating the capability of drivers to
safely operate a motor vehicle in the short and long terms. Driver behavior such as speeding,
reckless driving, and alcohol or drug use are typically addressed and closely monitored by law
enforcement authorities. Behavioral interventions such as stricter crackdowns on impaired driving,
additional restrictions on high-risk drivers and automated enforcement (10) have proved successful
in other nations
2.2. Probe Vehicles and Point Detection
Probe Vehicles and Point Detection (GPS, Video Detection, Radar, Transponders, Bluetooth
MAC Readers)—Doppler radar, video image processors (VIP) and Global Positioning System
(GPS) are technology devices that are used by roadway agencies for vehicle detection in order to
provide near-real-time travel time estimation. The application of each technology varies among
agencies according to agencies’ knowledge of each technology (11).
Doppler radar works by measuring changes in frequency and wavelength of moving targets. This
sensor is usually installed on a pole or a mast along the roadway and is capable of detecting speed
of vehicles moving toward or away from the radar. Doppler radar provides direct speed
measurements, and is typically insensitive to inclement weather.
A VIP system typically consists of one or more cameras mounted on a pole, a microprocessorbased
computer for digitizing and processing the imagery, and software for interpreting the images
and converting them to traffic flow data. VIP systems are able to monitor multiple detection zones
and provide information on several aspects of travel data (e.g., speed, volume and vehicle length).
Rain, snow, and wind gusts are known to affect sensor performance. Vehicle shadows and
occlusions are other weaknesses of VIP systems.
GPS is a worldwide tracking system based on satellites that orbit the earth. GPS receivers are able
to establish a vehicle’s position, speed, and direction based on satellite information. Continuous
vehicle position information is provided because vehicle direction and speeds are measured in real
time. The receiver is usually placed inside the vehicle and a dedicated data link (e.g. wireless or
cell phone network) is required to identify vehicle direction of travel and speed. GPS receivers
need to have a clear sky to receive signals from the satellite system, and the connection can be lost
when vehicles travel through tunnels, mountains, trees, etc.
ADDITIONAL DESCRIPTION AND QUANTITATIVE BENEFITS OF TRAVEL-TIME RELIABILITY STRATEGIES Page F-2