Posted On: Saturday - August 8th 2026 11:10AM MST
In Topics: General Stupidity Science Peak Stupidity Roadshow
That's an induction loop embedded in the pavement. These are everywhere. Nope, this is not an Orwellian Stupidity post. Unlike Flock cameras, and all the rest of the surveillance network around us, these output no information besides a change in current from an inductance change, based on a steel mass above them, for purposes of controlling stop lights, gates, or the like.
I'd thought they were even simpler than this, but wiki has a decent description:
When a vehicle passes over the loop or is stopped within the loop, some of the vehicle's ferrous body material increases the loop's inductance, in the same principle as including a metal core within a solenoid coil.That's fine, but what if you're on a bicycle? There's one gate that I have to get through that uses key-cards for entry and has one of these sensors for exiting. I used to be able to trigger it by riding the bike in a very tight holding pattern. Then, the thing was set less sensitive, so I had to get off the bike and move it near the ground over the loop. Now, that doesn't work, and I must climb the fence to get out, use the card, and get my bike outside... or ride around to a walk-through gate.
However, the peripheral metal of the vehicle has an opposite effect on the inductance due to eddy currents that are produced. The decrease in inductance from the eddy currents more than offsets the increase from the ferrous mass of the engine, and the net effect is an overall reduction in the inductance of the wire loop. The decrease in inductance tends to decrease the electrical impedance of the wire to alternating current. The decrease in impedance actuates the electronics unit output relay or solid-state optically isolated output, which sends a pulse to the traffic signal controller signifying the passage or presence of a vehicle.
At traffic lights, these induction loops can be a problem for people riding motorcycles, bikes, scooters, and the like. Traffic lights are set up for various modes of operation, and this is a good thing. I'm so used to the, well, not "smart" lights, as "smart" has its own connotation now, but let's say fairly bright traffic signals, such that any purely timed one with no traffic passing through on the crossing road irks me now. It's wasteful. ("How dare you!" I exclaim.)
For many years, a nearby small signal light has been set up to have the slightly busier crossing road normally green. It WILL NOT turn green for our road unless the loop is triggered. There is some timing involved too: Our road stays green for 10 seconds, I'd figure*. Then, if it just went back to red, you can't make it green again for another 30 seconds or what-have-you. It all happens in that galvanized steel box on the one corner. The loops must work though.
I used to walk my kid through this intersection when I'd bring him to and from school. It's been a decade now since we both watched a grown man on a bicycle waiting there for a green light. There were no cars in sight. I told the gentleman nicely, "You've got to run this light. It won't change till a car comes up". (I wanted to teach the boy how this works anyway.) He didn't like my lawbreaking advice one bit! He didn't like my lack of respect for the Authoritah of this traffic signaling device. We had a few words even. I still see him ride, but I've not gotten to see how he handles the light ten years later. Has he learned anything, or does he just show up late to work?
The next incident involved my pulling up behind a car that ws hanging back from the intersection behind a bike. I try to give other bicyclists plenty of room too, but unfortunately that car was too far back to trigger the light. We were all going to be sitting there awaiting a car from the other direction for who knows how long. I went around both just to get a small portion of my vehicle over the loop. The driver went into a rage, even after I explained to him how things work.
Lastly a 10-15 y/o (I can't tell) Indian girl on a bike was there the other day. I pulled by her and over the loop. Her parents must have told her to NEVER NEVER go through a red light. I told her through the open window that she'd be there a long long time if no car triggered the loop on in the pavement. I don't think she gets this... but I bet she can spell "induction loop", "Eye, enn, dee, you, see, tee, eye, oh, enn, ell, oh, oh, pee, induction loop".
Common sense has lost out to rote memorization and respect for electrical authoritah, it seems. Inductive stupidity.
* I've seen that some of these more bright traffic lights are set to keep a green longer if more traffic is flowing at the time. You don't need AI or even a massive bunch of software to help traffic move lots more efficiently.
Comments:
The Alarmist
Saturday - August 8th 2026 7:26PM MST
PS
I thought putting the tire rims parallel to the wire might cause enough induction, unless you have carbon fiber wheels. Another thought is to try a few winds of magnet wire, with the ends shorted to one another, on the inside of the rim to create an electrically larger inductor.
I thought putting the tire rims parallel to the wire might cause enough induction, unless you have carbon fiber wheels. Another thought is to try a few winds of magnet wire, with the ends shorted to one another, on the inside of the rim to create an electrically larger inductor.
Moderator
Saturday - August 8th 2026 5:34PM MST
PS: See, that's what used to work, Alarmist, as I wrote in the post. I'd hold the bike near to the ground and move it along the loop a bit. Probably the crank, being a decent chunk of steel (this is no super-lightweight racing bike) was what did it. This works no longer.
This is inside, well, a "secure area", one might call it. On the road, when I'm on my bike, this whole thing is not a factor, as I run plenty of red light that DO turn green. My only goal is to keep away from the cars. Just the other day, I had to go about one block on the sidewalk on this one road on which it'd be suicidal to ride on the road between angle-parked cars and the 2 narrow lanes of traffic on that side. A lady had been looking at her phone and finally looked up as I passed her on the side that worked best. "This is a sidewalk!" "Yeah, I get that.", I replied, with neither an inclination to argue nor explain.
Yes, there are laws in my State to help out motorcyclists, especially at big intersections that also require triggering of the loops. If I got it right from a friend who got a ticket long ago at 2 in the morning before this law, you are supposed to wait 2 minutes. If the light doesn't change by then, and there's no traffic, it's legal to run it.
This is inside, well, a "secure area", one might call it. On the road, when I'm on my bike, this whole thing is not a factor, as I run plenty of red light that DO turn green. My only goal is to keep away from the cars. Just the other day, I had to go about one block on the sidewalk on this one road on which it'd be suicidal to ride on the road between angle-parked cars and the 2 narrow lanes of traffic on that side. A lady had been looking at her phone and finally looked up as I passed her on the side that worked best. "This is a sidewalk!" "Yeah, I get that.", I replied, with neither an inclination to argue nor explain.
Yes, there are laws in my State to help out motorcyclists, especially at big intersections that also require triggering of the loops. If I got it right from a friend who got a ticket long ago at 2 in the morning before this law, you are supposed to wait 2 minutes. If the light doesn't change by then, and there's no traffic, it's legal to run it.
The Alarmist
Saturday - August 8th 2026 5:25PM MST
PS
Try putting your wheel rims over as much of the inductor as possible. If that doesn’t do it, tilt the bike so that the chain is close to it. Something on your bike might be ferrous enough.
If it was just a traffic light, a lot of places will not hold it against you if you come to a full stop and then go if it doesn’t change for you.
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Try putting your wheel rims over as much of the inductor as possible. If that doesn’t do it, tilt the bike so that the chain is close to it. Something on your bike might be ferrous enough.
If it was just a traffic light, a lot of places will not hold it against you if you come to a full stop and then go if it doesn’t change for you.
🕉
Moderator
Saturday - August 8th 2026 5:15PM MST
PS: Well, I don't want my bike hacked up too bad, Alarmist.
This fence, hence, the gate, is a 7 footer or so. I can still climb up it by the poles where there's no barb wire, but bringing the bike with me with one hand is something I could have done only going back 20 years..
I can leave a piece of steel nearby for this and hope nobody picks it up, but I haven't gotten around to that.
This fence, hence, the gate, is a 7 footer or so. I can still climb up it by the poles where there's no barb wire, but bringing the bike with me with one hand is something I could have done only going back 20 years..
I can leave a piece of steel nearby for this and hope nobody picks it up, but I haven't gotten around to that.
The Alarmist
Saturday - August 8th 2026 12:11PM MST
PS
The principles of Peak Stupidity would posit simply throwing the bike over the gate.
Follow me for more useful life hacks.
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The principles of Peak Stupidity would posit simply throwing the bike over the gate.
Follow me for more useful life hacks.
🕉
Why not drill a few holes in the rubber/epoxy filler, near the corners, and pour salt water in there? 🙃
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