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Inductive loop detectors are one kind of traffic sensor used to identify the different vehicle classes using the induced current from the loop of a wire which is fixed to the pavement. These are extensively used in highways as they possess very high accuracy and are economical as well.
There are various types of detectors available based on their functionality and usage. They are Pressure type, Push button type, Magnetic, Magnetometer, Inductive loop, radar type, sonic type, radiofrequency type and light emission detectors. Out of all these Inductive loop and magnetometer types are widely used for various purposes.
Inductive loops are very much useful in transmitting the signals by identifying the presence of vehicles passing through the loop. The entire process in which loop detectors work is depicted below.
Inductive Loop Mechanism
There are mainly three components for loop detectors that govern the entire mechanism.
There are various types of detectors available, out of these inductive loop detectors are widely used by traffic engineers due to their and higher accuracy and a wide variety of applications. The most common inductive loop detector applications fall into six categories and are described below.
Inductive loop detectors can be used for isolated intersections to regulate the flow of traffic without considering the operation of adjacent street signals.
Inductive loop detectors used in open arterial networks ensure that the traffic progress along a roadway by the display of successive green signals for the flow of traffic.
In closed networks, Inductive loop detectors coordinate a network of intersection signals within a defined area such as the city’s Central Business District (CBD).
In this type of system, all of the traffic signals within an area will be treated as a single system. Individual signals within this area may be controlled by using isolated intersection network concepts.
Inductive loop detectors help in identifying certain vehicles such as ambulances, fire trucks and buses more continuously through busy intersections.
At busy intersections where pedestrians hardly get any time to cross the signals, inductive loop detectors can be used in pushbuttons to give the right of way to the pedestrians.
Inductive loops used for traffic signal operations are of three types and are described below.
These types of signals are having fixed cycle lengths irrespective of traffic flow along the arms.
Based on the actual traffic length, loop detectors will decide the cycle length for the signal.
These types of signals are a mix of Actuated and pre-timed signals in which the mainstream traffic will have a fixed cycle length and the cross street will have actuated signal for the incoming traffic.
Inductive loops can be triggered when a heavy metal object or vehicle passes through the loop placed over the pavement. When the vehicle moves over the loop or stops over the loop it will generate a vortex current in the loop and thus decreases its inductance. The reduced inductance activates the electronics element output relay, which sends a current to the controller to inform the presence of a vehicle.
Inductive loop detectors are generally economical and hence they are widely used for various applications. Typical inductive loop detectors cost around Rs.1000/piece to Rs.10000/piece in India. Prices may vary from country to country based on the manufacturing and transportation charges etc.
There are some recent advances that can serve as alternatives for Loop detectors. They are described below.
This consists of a cylindrical road sensor containing a transducer and a radio frequency emitter with antennas and a battery. The inroad sensor is powered by an internal battery and it is connected to a relay by a radio link.
This contains a single video camera with processing hardware & software to provide data similar to a multiple loop detector.
In this type of detector, a microwave sensor is mounted onto the gantry/ pole so that when a vehicle passes through this a microwave beam is projected towards the vehicle and based on the reflected microwave the vehicles can be classified.
This is also similar to microwave detectors only but in these ultrasonic waves will be used to project onto the incoming traffic and the reflected waves can be analysed to differentiate the various vehicle classes.
Infrared vehicle detectors will be of two types; one is passive and the other is active type. Passive type detectors simply measure the vehicles by their motion while active type detectors are based on the reflected light from vehicles. All the specifications and design-related concepts can be adopted from the Federal Highway detector Handbook.
I hope the blog provides you with adequate knowledge of Inductive Loop Detectors and their associated features.
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