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Traffic Light Sensors not tripped by Model S


Feb 2, 2013
Orlando, Fla.
There is at least one red light that will not change when I pull up with my Model S. I've been stopping at the same light for 7+ years without issue (in ICE cars)...

I saw that some Roadster folks had this issue - anybody else run into this with the Model S? I've been making the right on red as a workaround...


Well-Known Member
Aug 7, 2012
Toronto, ON
There is a roadway sensor in my company's lot to open the gate when I leave, and my Model S seems to be able to trip that just fine. (It is a wire embedded in the asphalt, not a pressure sensor)


Electron tamer
Mar 27, 2012
Redmond, WA
There is at least one red light that will not change when I pull up with my Model S. I've been stopping at the same light for 7+ years without issue (in ICE cars)...

I saw that some Roadster folks had this issue - anybody else run into this with the Model S? I've been making the right on red as a workaround...

The sensors embedded in the pavement are wire loops that sense ferrous metals. We who drive motorcycles have this problem occasionally. I know the MS is mostly aluminum, which probably won't trip the traffic light sensors, but I thought the battery pack enclosure was steel for rigidity and safety. Being so low to the ground I would think there would be good coupling to the loop so it would sense the battery pack.


Dec 28, 2011
Saratoga, CA
I thought I was the only one that noticed this, but I'm not sure I'm ready to pin it on my Model S.

There are two traffic lights here in Saratoga CA that I stop at regularly, and I have had issues with the sensor tripping. (for those that live around here, left turn from CA-9 to Fruitvale Avenue, and left turn from Saratoga Avenue to CA-9 in the middle of town).

These are multilane roads and left turn signals, so I don't have any good options except to try to go straight across after the lights have cycled a few times.

AFAIK this has happened only when driving my Model S, and particularly after some rain. I've even seen it when I have had cars behind me in line (and I thought the sensors extended more than one car length).

I'm not ready to blame the MS for this yet, but is awfully coincidental. I would think that the steel plate on the bottom of the battery would be enough to trip the sensor.



Recovering Member
Apr 3, 2011
Northern Virginia
+1 @Captain_Zap

A friend of mine installs the loops here in FL. Basically, the wire has a light current which generates an EMF, when the EMF is disturbed by a bulk of metal (or a magnet) the change in the field trips the light. There are thousands of these in FL and I used to ride a motorcycle which generally doesn't have enough metallic mass to trip the sensors. Tripping the loop does not require ferrous metal, it just requires that the metal be capable of conducting electricity to trip the sensor through inductance. What really drives us nuts here in FL are the number of people who stop 20' before the lights and then wonder why they don't change; well dohhh, they didn't drive on top of the induction loop.

I don't see any reason why a Model S wouldn't trip an induction loop and we've had no problem here, even though Sarasota has them at virtually every junction. There are a couple of tricks that motorcycle riders have, one is to put a magnet on the bottom of their bike frame (see here) and the other is to stop about 2/3 of the way towards the side of the loop so that the bike isn't exactly in the middle of the EMF. Try stopping off-center and see if that makes a difference.


Model S 03182
Jan 13, 2012
Atlanta, GA
My dad is a traffic engineer. He designed many intersections with these induction loops in the road. Nigel is pretty much right on their operation. They only require a electrically conductive mass (better a loop) for them to detect. I had a friend that carried around a foot long piece of 1" rectangular hollow steel that would work every time for induction loops.

I also ride bicycles often. And there is a trick to getting the induction loops to pick up a bicycle. And my bicycle has almost no iron on it at all. If you are directly over a portion of the coil (what motorcycles have a problem with) you just tilt your wheels (large aluminum, or carbon fiber, conductive loops) such they are not perpendicular to the surface of the road and you get picked up. So the Model S being aluminum isn't a problem.

Now they don't even use inductive loops. They use low resolution cameras. They are little white things perched on the signal mast arms, or signal poles. Install cost is so small, and maintenance is also much cheaper. These are tougher to figure out as there are no indications of what the programming is looking for, or what locations it has zoned.

Most likely is that the loop failed around the same time you got your car, or the signal timing got changed. And it seems like your car isn't getting picked up. There plenty of metal, and even plenty of steel to get picked up. And the car is plenty wide enough to sit directly above a piece of the loop.
Mar 11, 2010
Humboldt/Los Altos
we have loops sensitive enough for bicycles now in some areas. It depends a little on the setup of the loop a for the sensitivity that it can have. Some loops are cut in 25' long rectangles near the wheel paths and others are circles/octagons. There are typically a few sets of loops for each lane. Sometimes there are problems where there might be a turn lane next to a through lane with loops too close to each other. The sensitivity can't be high enough that the turn loop is activated for through traffic or vice versa

cameras such where it is windy / foggy or lots of changing shadows, but they are getting better with the software


Lead Moderator
Apr 2, 2010
Ottawa, Canada
An inductive loop can detect both ferrous and nonferrous metals. Ferrous materials amplify the applied AC magnetic field. In nonferrous metals the field induces currents in the metal, which create an opposing "scattering" field. Essentially it has the opposite effect to the ferrous materials. (Depending on operating frequency there can also be a phase shift with nonferrous materials, depending on a bunch of factors.) It is highly unlikely even for a mixture of materials to not be detectable, because at the very least the result would be lossy.

So if the electronics are properly designed, and functioning correctly, they should be able to detect either type of material.

Also, around here something like 90% of the intersections have detector loops, and I've never once had a problem.


Jun 20, 2012
Most instesections I use have that same time of sensor in the pavement, and I ahve had a problem with my Model S.

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