How does an automatic road barrier decide when a vehicle is coming?

tired_lemming@sh.itjust.works to No Stupid Questions@lemmy.world – 43 points –

So just something that's been on my mind. At my workplace there's an automatic road barrier that lifts up and down when vehicles arrive. However, it's not used for a carpark system when people wave their tickets or something. It just goes up and down when a vehicle shows up.

However, it sometimes goes up for when say a pushcart is being rolled over whereas it wouldn't for a guy pushing a bin.

So tldr, how does an automatic road barrier decide that yes, a vehicle is coming, and therefore opens up?

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Same as traffic lights. "Inductive-loop traffic detectors use an electrically conducting loop embedded in the pavement to send a signal to the traffic control system to indicate the presence of a vehicle."

So a large wooden horse could slip by without detection

If the large wooden horse is full of men in metal armor, purely hypothetically speaking, would the loop still not pick up the large wooden horse?

Technically speaking it would pick up the men in metal armors, not the wooden horse per se.

But the barrier would lift for the wooden horse full of men in armor indeed.

Depends on how high on their horse they are: They might be too far away to trigger the sensor.

This, it's like a metal detector but, bigger. Temporary boom gates might use infrared motion sensors like automatic lights. edit: "lights" like the lights some people have on their porch.

It's bigger in overall structure size, but isn't really that big itself. It's just a wire loop, they can be installed into existing roads with minimal effort - they just dig a narrow trench and then seal it up, it doesn't require more tarmac.

Huh, so that's a completely new concept I've learned today. Time to do more reading. Thanks!

Check the road in front of the gate. Those loops are usually installed after the asphalt so there should be a loop patched up with tar a bit smaller than a footprint of an average car.