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Some data to calculate vehicle gaps, intersection stop delay, stop sign delay,
and saturation flow rate, spot speed as a function of vehicle class, and travel
time when the counter is utilized in conjunction with a vehicle transmission
sensor.
Advantages
- Cheap and self-contained, the easiest to deploy of all intrusive systems,
recognized technology with acceptable accuracy for strategic traffic modeling
purposes, hence very widely used.
- Axle-based classification appears attractive, given sub-vehicle categories
are partially axle based.
Disadvantages
- Some units are not counted or classify vehicles.
- Tube installations are not durable, the life of tubes are less than one
month only.
- The tube detectors are not suitable for high flow and high speed roads.
- Units should not be positioned where there is the possibility of vehicles
parking on the tube.
- It can’t detect the two wheelers.
Inductive Detector Loop (IDL)
Oscillating electrical signal is applied to the loop.
The metal content of a moving vehicle chassis changes the electrical properties
of circuit.
Changes are detected at a roadside unit, triggering a vehicle event.
A single loop system collects flow and occupancy.
The speed can be calculated by the assumptions that are made for the mean length
of vehicles.
Two-loop systems collect flow, occupancy, vehicle length, and speed.
Advantages
- It is a very cheap technology. Almost every dynamic traffic control system
in this world uses IDL data.
Disadvantages
- Loops are damaged by utility and street maintenance activities or
penetration of water.
- IDLs with low sensitivity fail to detect vehicles with speed below a
certain threshold, and miscount vehicles with complex or unusual chassis
configurations, or vehicles with relatively low metal content (e.g.
motorcycles).
- IDL data supplied to traffic control systems have a very low sample rate.
- Not suitable for mounting on metallic bridge decks.
- Some radio interference occurs between loops in close proximity with each
other.
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