Hypno Toad

I've heard that a bike can trip a stop light sensor; however, I've never had this happen ... until today.

For background, I'm taking about the magnetic sensors in the road surface that detect if a car is waiting for the stop light. Typically, these lights will not change for bicycles (or even motorcycles). And you can know that the sensor is at the stop light if you're using a wireless cyclo-computer (always seem to be the same communications frequency and your computer will lose it's sh.... stuff)

This morning, I was making a left turn, the left turn signal will only go green on if there is a car waiting. However, today I got the left turn light. There was no car behind me. The best I can tell, it was my steel frame bike. I've only had this bike for a few months and haven't used it much. I also have a new steel frame fatbike (Pugsley), but I don't ride that on the roads much.

Anybody else able to get the green light with their steel frame bike?

Wilbur Bud

Well yes, sure, it's really more a case is the sensor adjusted to notice the available mass of the bike. Generally I think these sensing systems are not magnetic but are instead inductive, meaning they sense metal but it doesn't have to be steel. A good setup person will use a couple bike rims to set the low threshold. Willingness to do that depends on where you live and which agency has control of the intersection (State vs local usually). I'm lucky in that most of mine are responsive to a request to adjust, and in some cases will also offer to come paint a line to show where to put your bike to maximize it's ability to trigger.

Amp3rs4nd

I would contact your local transportation department. ALL lights with under asphalt detection systems should accommodate ALL road users including motorcycles and bicycles.

SouthFLpix

The steel bike yes, but I have to park it right on top of the sensors. The aluminium bike is not detected. There was a device marketed on kickstarter that allowed easier detection of bikes at intersections, but it seemed gimmicky to me.

Edit: here is the link to that device I mentioned on kickstarter. Looks like it didn't meet its funding goal. https://www.kickstarter.com/projects...from-your-bike

Edit #2 : After reading through these responses I have tried again several times to trip the sensors with my aluminum bike, and have failed. I usually just look both ways and run the red.

Andy_K 

I usually have no problems triggering the lights that use induction sensors such as you describe. It's all about having your bike in the right place. This link gives some tips: Bikes & Pedestrians

Of course, the sensor has to be properly calibrated to work with bikes. I'm lucky in that the local roads department is very responsive to requests to fix this sort of problem. YMMV.

I have more trouble with the lights that use cameras to detect traffic. These also depend on your placement on the road (waving your arms like an idiot helps too) but it's far more difficult to figure out where you should be. Sometimes I can get the county to come out and paint a marker on the road where a bike can trigger the light. Sometimes they just adjust the sensitivity. I've got one light on my route that I just can't get to work -- except a night...shining a light at the sensor usually does the trick.

HardyWeinberg

Andy_K 

Also of posisble interest: Bike Science: Making sense out of traffic signal sensors - BikePortland.org

Phil_gretz

Yes. Ride down the center loop, over the groove. Works every time.

HardyWeinberg

I commute through 2 municipalities, and the one where my office is, they are disconnecting all the inductive loop sensors and replacing them with cameras. So using the bike placement illustrated above I can always trigger the inductive loop sensors, but the camera sensors just don't see bikes, ever. I assume that's a calibration thing. I've tried weaving across the lane back and forth as I roll up to it, trying to make myself bigger, but no luck.

Hypno Toad

First, that's everyone for the correct, it is inductive not magnetic sensors (sorry, I hadn't had enough coffee when I posted that).

I have tried the bike placement methods with no success - even with some lights where you can see the cuts in the pavement to know where the loop is. I've only had aluminum frame bikes until late last year. I use the intersection in question daily on my commute and that's why it really surprised me when the light triggered today without a car behind me. My only guess was that the steel frame made a difference. I could be that I had the placement just right (by dumb luck).

I will contact the local dept of works, my guess is I will get little interest from them... But as a home owner I might be able to press the issue with more force.

RR3

My bike doesn't trip sensors because I have no traffic lights to deal with.

tsl

I can trip them with both of my aluminum bikes and my titanium one.

If I can't, I report it to the county and they fix it.

Remember that the detectors don't detect magnetism, and they don't rely upon mass. They're a simple metal detector, just like the ones those guys use at the beach, only turned upside down. Metal detectors will detect all metals--gold, silver (which is what they're after), copper (which is why utility companies use them), aluminum cans and pop tops, zinc, and yes, even steel.

Mr IGH

Here in Longmont my steel framed road bike trips inductive loops.

I've heard that the City of Boulder Colorado's cameras detect bikes but I can't find any proof on-line. Going forward I expect the cameras will detect bikes eventually.

ItsJustMe

All bikes can trigger sensors unless they have carbon fiber rims. The question is rather "are the lights on your route properly configured, or do they not trigger for bicycles?"

Also here's the full article the illustration above comes from:

Detection of Bicycles at Demand-Actuated Traffic Signals

TroN0074

Currently wireless detection is the trend with the transportation agencies across the country. the devices that are being installed are capable to detect bicycle but it is up to the installer to set them up that way. The sensors are manufactured by a company called Sensys Network here is the link so you can read about it

MicroRadar® | Sensys Networks

Wired loops are old and if the intersection has been modernized from the last 5 years chances are the wireless access points are installed in place.

Good luck to you.

Squeeze

I don't know if my bike trips sensors or not, because if there are no cars around, I just go press the pedestrian walk button and then get back in the lane and wait for the green light. That works every time.

Hypno Toad

Left turn lane?

I have done this often when going straight at a light. In fact, I recall a couple times using the beg-button when there were cars and the light wasn't changing - so the biker was helping the cars. HA!

Andy_K 

I really hate doing this. It takes you out of the normal line of sight and its generally awkward. At high traffic intersections I suppose it is workable. At intersections with sparse traffic my experience is that it often switches the light almost immediately, leaving my facing the wrong direction and trying to get turned around and in position to cross the intersection before it changes back again. If a car happens to come along while I'm stumbling through this clumsy dance, it feels dangerous.

There's one intersection on my commute with a bike-specific button that's just inside of the curb and the way it's positioned makes this feel even more unsafe than the ped buttons. It's back about 15-20 feet from the intersection on a road with no shoulder and a lot of right-turning traffic. I want to go straight through the intersection and would prefer to take up a position to the left side of the lane that allows the right turning traffic through. If there are no cars at the intersection when I arrive and I cruise over to the bike button a car can come around me from behind and effectively trap me against the curb, unable to reach either a reasonable lane position or the pedestrian waiting area on the corner (unless I climb into the grass and walk there).

prathmann

The town just south of us is replacing their inductive loop detectors with microwave sensors that sit on the traffic or light poles at an intersection. Not only does the new system reliably detect bicycles, but it distinguishes them from other traffic and is connected to the traffic light controller to extend the time for a yellow light if a cyclist is in the intersection so he'll have time to clear the cross road before traffic there gets a green.

Squeeze

No, not left turn lane, and not at high traffic intersections, either. I suppose every situation is different. I do it at two quiet neighborhood streets that cross major boulevards. They're the kind of intersections that never get a green light unless someone is waiting, and even then, it's a LONG wait when I arrive in my car. I get through faster on the bike when I press the button. I've considered jumping out of my car to press the buttons at these two intersections, too, but never have.

ericy

I have this problems in the mornings - our community has a gate that is closed from 9PM->6AM, and if I leave the house before 6AM the gate is closed, and the sensor won't pick up that I am there.

There are two workarounds that I use - I can just ride the sidewalk past the side of the gate (yes, the gate is really that useless), or I can just sleep a little bit later so that the gate is already open by the time I get there.

CliffordK

Sometimes it trips them. Sometimes it doesn't. Sometimes I'm left waiting for a car to come up behind me (hopefully they don't stop 50 feet back, behind the sensors).

My heavy cargo bike + trailer is more likely to trip the sensors than my road bike.

Not being able to ever trip the lights does make for bad left hand turn habits

Andy_K 

That's a nice feature!

locolobo13 

On my normal route there is only 1 trip sensor. When I first started riding this route the light wouldn't trip no matter what. I don't think it had been set for bikes yet.

A few years ago riding up to the light I noticed the "Don't Walk" sign blinking for cross traffic. That's usually a sign the light is about to trip. It would count to 0 then go back to "Walk" without tripping. Eventually I found the sweet spot. Now if there are no cars I can trip the light.

cyccommute 

I've found that I have to be directly over the longitudinal wire shown in the illustrations that HardyWeinberg stole from here. If you can ride the entire length of the wire...especially the center wire of a dipole loop...it helps trip the signal. Stop with your wheel directly over the wire as well.

Motion sensors are hit or miss. I have a camera based motion system near my work that won't detect me during the summer no matter how big I make myself. And calls to the local municipality...even those made by the largest employer in their town...fall on deaf ears.

I don't have trouble tripping it during the winter because I shine my helmet light on it.

Yup. And that is why it doesn't matter what material the frame is made of. The frame isn't being detected. The wheels are being detected. The sensitivity is related to the mass of the material and bicycle wheels have low mass so they need to be as close to the most sensitive part of the loop as possible.

That has to be the goofiest and dumbest thing I've seen. The wheels on the bike will do just as well. If they made it longer, you could use it as a kickstand