Road Cycling - Triggering Lights at Interesections

This is about the detectors at some intersections...the ones that require the presence of a car to trigger a green light. How do they work? Is it possible for a bicyclist to trigger them, rather than wait for a car to come along?

The answer is yes, sometimes. Here's an article copied from The bicycle FAQ (http://www.faqs.org/faqs/bicycles-faq/part4/). In my experience, contrary to what the article says, the sensitivity can't always be increased. Or maybe the DOT engineer just didn't want to, and lied. Anyhow, first step is to be sure you're running over the sensor.

Subject: 8i.2 Traffic detector loops
From: Bob Shanteau <shanteau@iname.com>

A traffic loop detects metal objects such as cars and bicycles based on
the change in inductance that they induce in the loop. The loop is an
inductor in an LC circuit that is tuned to resonate at a certain
frequency. A metal plate over the loop (like a car) causes the magnetic
flux to be shorted, reducing the inductance of the loop. This causes a
change in resonant frequency, which is detected and sent to the signal
controller. One of the ways of testing a loop is to create a loop about
2 feet in diameter with several turns of wire (connecting the ends) and
placing the test wire in the middle of the traffic loop. The test wire
should cause a dectection, if all is working.

The same effect is seen with a vertical piece of metal, such as a
bicycle, but is weaker. Because aluminum conducts electricity quite
well, aluminum rims help. Steel rims are OK. Non-metal rims cannot be
picked up at all. A bicycle with aluminum rims will cause about 1/100
the change in inductance of a car.

It is always possible to set a detector's sensitivity to pick up a
bicycle. The trade-off is in longer detection times and the possibility
of false detections from vehicles in adjacent lanes. Most people who set
signal detectors use the lowest sensitivity setting that will pick up
cars reliably.

I advocate using the highest setting that will avoid picking up vehicles
in adjacent lanes. Digital circuits used in modern detectors can use
high sensitivity settings without unacceptable increases in detection
times. Unfortunately, there are still a lot of old detectors out there,
and most people who work on signals use principles based on the
performance characteristics of old detectors.

In any case, bicyclists should, as a general rule, place their wheels
over one of the slots to maximize their chance of being detected. That
is where the magnetic field perpindicular to the wheels is strongest.
Bouncing the bike or moving it back and forth does no good. If you have
a metal frame, another tactic that may work is to lay the bicycle down
horizontally inside the loop until the light turns green.

Advancements are under way that may make traffic loops obsolete some
day. In particular, radar, infrared and sound detectors have been
introduced. Systems based on video cameras are especially promising.
Such systems can easily detect bicycles. Such a system may even be able
to detect pedestrians some day.

Bob Shanteau, PhD. PE
Registered Traffic Engineer

if your bike does,nt trigger the pads ride thru the red when its safe to do so. if the pads dont work for a bike & bikes are allowed on the road then the lights are faulty! what would you do in a car if the pads did.nt change the lights ?:rolleyes:

I've had mixed luck at getting those d@mn induction loops to work for me. The old hybrid I used to commute with usually set them off ok, even the tricky one at the rear gate where I used to work. The C'Dale touring bike was a bit trickier, but my road bike was not much at setting induction loop switches off.
I find that repetition often gets these things to work eventually. Riding in a small circle, 3 or 4 times over the loop always eventually tripped the switch on the gate, which sure beat having to unclip. press the button, then run around the gate as it opened.

In the San Jose, CA area and up the peninsula, the transportation department has painted the symbol of a bicycle over the most sensitive spot of the induction loop. It seems to work pretty well, as I have seldom had to run the red light, 'tho it does happen occasionally.

I never saw this type of road marking when I lived in the D.C. area. Any other places have similar lane markings to help cyclists trigger the traffic signal?

they have these "Smart lights" all over where I live. I have only been stuck at one once. All of the ones that I have seen are infrared. I can clearly see the detector. For you guys that ride in the Baltimore-Washington area, there is one on the intersection between route 99 and 32.

I pulled up, waited for about 5 or ten minutes, sort of fuming, until I realized it was a smart light. There was a ford excursion behind me, probably also fuming, and then I decided that I would just turn around and go to the back of the line of cars. the excursion pulled up, and It tripped the light, and I rode through next to the SUV.

There is one near the bottom of my street, and sometimes, when my dad is in his convertable, it won't work. These "smart lights: need some refinement.

Out here in T.O., theres a botton where pedestrian can accelerate the light change, sometime I will go down my bike and will try to activate this botton, and I will always get a smile in my face, when I do that. he he:D :D :D

I awlays end up waiting for a car to come or having to run the light (never more than a minute or two). I always thought it was the weight of the object that triggered the wire which would defidently rule out bikes when trying to change the light. I also ride an aluminum bike but no luck with setting it off:rolleyes: .

I've heard that some have luck at triggering lights, when they lay their bike down on the sensor... never tried it myself though :rolleyes:

You can buy magets to put on your bike that can help trigger the lights (I hope it doesn't interfere with the speedometer!). They are sold for motorcycles and bicycles. Also laying the bike flat on the ground can help trigger the lights. That's what they say to do at the parking garage near me to set off the detector.

I've seen two kinds of sensors around here, both using wires cut into the pavement.

One looks like this:

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And one looks like this:

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The first kind, the single box, is difficult for a bicycle to trigger. The second kind, though, can be triggered if you ride slowly along the center wire and stop above it. I imagine there are differences in sensitivity, but all of the double box ones I've seen can be triggered by the bike.