How to use ir transmitter/receiver to count parallel vehicles

Hi: I plan to use an infrared sensor transmitter/receiver to calculate the number of vehicles. This is my idea: - Use 8 pairs of transmitter/receiver infrared sensors - The distance between each pair is one meter - If at least 3 pairs of consecutive sensors detect the signal at the same time, it is judged that the vehicle passes (normal car width is about 3 meters) - If 4 pairs of consecutive or more pairs of sensors detect a signal, two or more vehicles may pass in parallel. It is easy to calculate the vehicles one by one. But I have no idea to count how many vehicles pass in parallel? Any suggestions?

What are these vehicles that are passing in parallel? Parallel to what? Each other? Or parallel to your sensors?

Paul

Just like I painted. Two cars pass in parallel through the transmitter/receiver sensor. At this point, the three pairs of connected sensors simultaneously detect the signal. So I know that the vehicle passed. But the problem is that two cars pass side by side. I don’t know how to make sure there are two cars.
Do you have some suggestion?

Detect the cars from overhead with a LIDAR positioned to read each lane. A LIDAR overhead, a time of flight sensor, would give a flat reading when 0 car present which would then be used as a 0 car present in lane reading. Once and as long as there is a deviation from baseline reading there is a car present under the sensor.

This is probably a silly question, but if the two cars have different lengths, are they still parallel?

Paul

It's hopeless. Use what most departments of transportation use for counting vehicles: pneumatic road tubes.

Check out this for more info.

Most motor vehicles are way longer than 3m. More typical is 3-20m (from a small compact car to a long truck). That alone will make your scheme fail.

If you must do it from the side, I’d place a single distance sensor on either side. Measured distance >2m: no vehicle passing in that lane. <1m: vehicle passing. There will be space between two vehicles, so the end of one and the beginning of the next is dead easy to find with a single sensor.

If you need to know the speed, place two sensors at some distance next to one another, so you can measure the time it takes for the vehicle to travel that distance.

Ultrasound or IR will both work fine. IR is much more sensitive to ambient light (sunlight is a major problem) but faster than ultrasound. For just counting, ultrasound. For speed, IR.

Right! Using a distance sensor is really helpful. In fact, I don't have to calculate the exact number. This method is indeed more telling that the car may be driving side by side. Thank you!