There are many types of vehicle detectors and sensors available. Which one is the best. It depends.
Inductive Loop Detector: Loop detectors, with regular preventative maintenance of checking loop operation and condition, provide good service. In addition, the loop detector can be designed to detect field wire problems and go into a fail-safe condition. Loop detectors can detect vehicles of all sizes and shapes, classify vehicles, determine speed, and discriminate vehicles. Detection zone is made specific due to physical location but there can be adjacent lane detection, especially with improperly installed loops. They do require some form and quantity of metal to allow detection. They can provide vehicle discrimination, vehicle counting, and special vehicle detection.
Video Detectors: There are several types of video detection. Many claim to be able to detect vehicles under all conditions. That is probably an exaggeration. Video detection systems can be weak, in my opinion. There is a chance of not detecting a vehicle, especially during twilight periods or bad weather. Since there is no exact way of knowing when a vehicle is left un-detected some other means of guarantying service is needed. In order to assure service of all approaches in a “fail-safe” manner, all phases using video detection would need to be left on vehicle recall. When video detection systems are used, their operation needs to be regularly checked. If there are any video alignment changes, they should be corrected. Since they are optical, lens and enclosures should be regularly cleaned. Video detection has problems with occlusion of the detection zone and detection of shadows.
There are simple and complex microwave detectors. Simple detectors are point and shoot. Aim them at the vehicle approach and they provide a contact closure when a vehicle passes through the detection zone. Most only detect moving vehicles and can’t provide a presence detection output.More sophisticated microwave detectors like the Wavetek can do much more. They can provide complex conditions for the turning on the outputs to the controller. Vehicle speed range and detection zone can be used. They seem ideal for detection of vehicle queues and platoons. They are limited in that there is no way to isolate lanes so left and right turning vehicles are included along with through traffic. Manufacturers claim that weather does not affect the operation.
So, What’s Best?
It really depends on the intended use. Traffic signals should be “fail-safe.” That’s where video and microwave detection systems are weak, in my opinion. If only one type of detection is used at an intersection, I believe it should be inductive loop.
This does not mean that video and microwave detection don’t have their uses. They can be effectively used for traffic sampling, vehicle counting, queue detection, vehicle tracking and more. The cost of installation may be lower for large installations. If lane changes may occur, they are easier to reconfigure to the new lanes. Damage due to construction activity will be much less since nothing is buried. The problem is that detection accuracy is lower than inductive loop detection and detection can’t be made “fail-safe.”
I know, I’m old fashioned. New technolegy is always more capable. Right. Not always. I find the old ways are often still the best or at least as good. I do like technology and think that when it is applied properly, does help with traffic management. I just wouldn’t throw away the old technology just yet. The right approach is likely a combination of vehicle detection methods.