Author Topic: Biking question - Left turns at stop lights with sensors  (Read 4662 times)

GuitarStv

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Biking question - Left turns at stop lights with sensors
« on: December 20, 2012, 09:36:46 AM »
We have many stop lights that operate by a sensor.  The sensor doesn't pick up my bike, so if I wait for a turn, I will be waiting until a car comes up behind me . . . could be 5+ minutes in some places.  What I have been doing is going over to the sidewalk and pressing the button, then crossing on the crosswalk walking my bike, stopping once I reach the far lane, hopping on my bike and continuing along.  This sucks though . . . there has to be a better way.

What do you guys do?

MustacheMike

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Re: Biking question - Left turns at stop lights with sensors
« Reply #1 on: December 20, 2012, 09:41:00 AM »
The loop embedded into the pavement responds to a magnet. In the case of cars, the hunk of steel itself is enough to trigger the loop to signal that there is a car waiting. Sometimes, motorcycles can't even trigger the loop, which is why some people recommend attaching a magnet to the bottom of their bike, so it will trigger the sensor.

http://www.youtube.com/watch?v=8GAacxGiV4A

Hamster

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Re: Biking question - Left turns at stop lights with sensors
« Reply #2 on: December 20, 2012, 09:57:42 AM »
I have one left turn on my commute where I can't trigger the sensor. I turn right instead, and make an immediate U turn. Then I go straight through the intersection (right plus U-turn = left turn).

I learned that trick in Taiwan, where it's illegal for motorcycles/scooters to make left turns at big intersections.

If there's already a car in the left turn lane, I just wait behind it so it will trigger the left turn arrow.

iamlindoro

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Re: Biking question - Left turns at stop lights with sensors
« Reply #3 on: December 20, 2012, 10:03:26 AM »
Assuming your bike isn't carbon, stop at the sensor, which you can often see the outline of (it looks like a 3x6 foot rectangle).  Lay the bike down such that the frame "connects" the two parallel lines of the sensor for a few seconds.  You will trigger the sensor this way without any extra gear.

MustacheMike

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Re: Biking question - Left turns at stop lights with sensors
« Reply #4 on: December 20, 2012, 10:36:18 AM »
Assuming your bike isn't carbon, stop at the sensor, which you can often see the outline of (it looks like a 3x6 foot rectangle).  Lay the bike down such that the frame "connects" the two parallel lines of the sensor for a few seconds.  You will trigger the sensor this way without any extra gear.

Smart! Do you have to touch the frame to the ground, or can it be a few inches above?

GuitarStv

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Re: Biking question - Left turns at stop lights with sensors
« Reply #5 on: December 20, 2012, 11:09:14 AM »
Not a carbon frame, but my bike is aluminium (I would figure most bikes sold these days are aluminum).  Being non-ferrous, I'm guessing that it wouldn't trigger the sensor either though.  :(

Hamster

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Re: Biking question - Left turns at stop lights with sensors
« Reply #6 on: December 20, 2012, 11:15:22 AM »
Not a carbon frame, but my bike is aluminium (I would figure most bikes sold these days are aluminum).  Being non-ferrous, I'm guessing that it wouldn't trigger the sensor either though.  :(
Ferrous shouldn't matter, as long as it's conductive. Even a carbon bike with aluminum rims should work if the sensitivity on the detector is high enough (not a given).

If you want more info about how the sensors work, and how to position your bike to trigger them, the link below shows you what to do based on the shape of the cut-outs in the pavement.
http://www.humantransport.org/bicycledriving/library/signals/green.htm

In theory you shouldn't have to lay the bike on the ground as long as you know where to position it to be noticed by the "inductive loop". Laying it on the ground gives you a better chance of hitting the sweet spot.

Where I live, anyone can call the city to have them check the sensitivity of the loop for bikes. I only have one place in my commute (happens to be the left turn scenario we're discussing), where I'm consistently unable to get my bike to trigger the signal, and the city (or I) just can't seem to figure out how to make it work properly.

GuitarStv

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Re: Biking question - Left turns at stop lights with sensors
« Reply #7 on: December 20, 2012, 11:21:47 AM »
Hmm . . . there are four or five places I regularly make left turns around town.  I'll give this a shot and see if I can get at least a couple of them to change.  Thanks!

BlueBeard

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Re: Biking question - Left turns at stop lights with sensors
« Reply #8 on: December 20, 2012, 11:22:00 AM »
Here in MN they address this for motorcycles.  The law says that you must wait a reasonable amount of time and then you can proceed through the intersection safely, as the sensors might not trigger.  When I rode, there were a few lights one right by my house that never picked up the motorcycle.  I assume this would apply to bicycles as well.  I am not sure what the laws are in other states, so you may want to check.  Also if it was a busy intersection you may have to come up with another strategy.

iamlindoro

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Re: Biking question - Left turns at stop lights with sensors
« Reply #9 on: December 20, 2012, 11:30:25 AM »
Assuming your bike isn't carbon, stop at the sensor, which you can often see the outline of (it looks like a 3x6 foot rectangle).  Lay the bike down such that the frame "connects" the two parallel lines of the sensor for a few seconds.  You will trigger the sensor this way without any extra gear.

Smart! Do you have to touch the frame to the ground, or can it be a few inches above?

It can be a few inches above.  I put one foot on the ground and "dip" my bike to the side so that the crank almost touches the ground between my legs.  (Everything else above is great info also, I hadn't seen that link about best practices per sensor shape)

capital

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Re: Biking question - Left turns at stop lights with sensors
« Reply #10 on: December 20, 2012, 12:51:38 PM »
In most states, it's legal to run the light (safely) if your bike doesn't trigger the sensor. You can also often contact your local DOT or the like and see if they can retune the sensor-- if there's a local bike advocacy organization, they might have info on how.

yolfer

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Re: Biking question - Left turns at stop lights with sensors
« Reply #11 on: December 20, 2012, 02:20:22 PM »
In most states, it's legal to run the light (safely) if your bike doesn't trigger the sensor. You can also often contact your local DOT or the like and see if they can retune the sensor-- if there's a local bike advocacy organization, they might have info on how.

In Seattle, I've had a lot of luck contacting the DOT. They even have a crew that comes out with a fake "bike" (it's just a bike rim/tire) to calibrate the sensor. Also, they'll paint a little T or X at the stop light, which indicates the most effective place to put your front wheel, in order to trigger the sensor.

We have a law that makes it illegal for a sensor to not detect bikes and motorcycles (I think). YMMV.