Dr. Paul
Russell and Dr. Jack Smith
Scottsdale, AZ
Report No. FHWA-AZ87-826
October 1987
The characteristics and sensitivity of inductive loop detectors have been predicted for particular vehicle configurations and have been established empirically through years of experience. This report summarizes the information available and extends the sensitivity versus height calculations to include different models for vehicles of varying size. The degenerative effect on loop sensitivity of reinforcing steel in the roadway has been calculated.
In the absence
of reinforcement, loop sensitivity is predicted to decrease at a rate
of 4% for each additional inch separation between the loop and the average
height of the vehicle. This decreased rate is independent of vehicle size.
Size and
magnetic field distribution essentially determine loop application. Large
loops exhibit reduced sensitivity to small vehicles. the magnetic field
distributions for a small 6' x 6' quadrupole loop is stronger near its
center. As a result it is more sensitive to small vehicles and provides
better lane discrimination.
A major
deficiency in loop theory is the lack of verification of results obtained
from calculations. To verify theoretical models, a detailed experimental
plan is presented.
The result
of successful experimental verification will produce refined design criteria
for determining presence, count and speed from inductive loop detector
applications.
key words:
loop detectors, traffic control strategy, traffic surveillance
This document is available to the public through NTIS, Springfield, VA 22161.
Last Modified: March 20, 2007
Maintained by: traffic@nmsu.edu
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