User Manual

Page 46
Figure 54. Permanent In-The-Road Traffic Sensor
Figure 55. Permanent, In-The-Road Traffic Sensor
Traffic Sensors
The U.S. Government is actively
studying "smart highways" as an
alternative to major new highway
construction. The idea is that
existing highways can
accommodate greater vehicle
densities if electronically managed.
In addition to conventional traffic
monitoring for highway studies
and enforcement, the Intelligent
Vehicle/Highway System (IVHS)
programs create the need for new
classes of "smart highway" high
speed sensors to count and classify
vehicles, provide lane control, and to monitor weight and speed. IVHS also requires "smart car"
sensors, and advanced vehicle surveillance, communications, and software.
Futuristic programs like the IVHS, and more contemporary projects like the Strategic Highway
Research Program (SHRP), require traffic data collection to provide the necessary information required
by the Federal Highway Administration on highway structures. Recent advancements in signal
processing open the door to greatly improved real-time vehicle data analysis, provided that inexpensive
reliable sensor technologies are developed.
Pneumatic road tubing has long been the workhorse of traffic data collection. Road tubes provide a
pneumatic pulse to a piezoelectric membrane, which triggers nearby electronics when an axle is
detected.
The evaluation of alternative
sensor technologies has shown
piezo cable provides the
necessary sensitivity, linearity,
noise immunity and
environmental stability for high
traffic interstate vehicle
classification and weight-in-
motion systems. Piezo cable BL
sensors are used for traffic data
collection from Saskatchewan to
Florida.
Piezo cable traffic sensor
constructions are shown in
Figures 54 and 55. There are
two basic categories of traffic
sensor ... permanent and
temporary. Generally,
permanent sensors are mounted in the road with the top of the sensor flush to the highway surface,
while temporary units are adhesively applied to the road surface for shorter monitoring periods.
Permanent sensors, used for toll booths and interstate highway data collection, are flush mounted to a
road surface and must withstand the rigors of years of high density traffic, snow plows, salt, sand, water
and dragging mufflers.