Monday, December 11, 2006

Pushing the Button & Signal Sensors

In a post today at BloggingLA, Sean tells the "Lady Standing on the Corner Pressing The Crosswalk Button Hundreds of Times" that she "only need[s] to press it once."

He's right: one push of the button will trigger the mechanism in LA City crosswalks. No need to hit it multiple times. It's like an elevator call button - pushing it multiple times doesn't make the elevator car come faster. And, unlike in New York, pushing LA buttons actually works. See, those that have buttons need them - it holds the "walk" or "PedHead" longer for pedestrians to cross. Sometimes, if the button is not pushed, the "PedHead" doesn't even appear. Those lights that ARE calibrated via the City's ATSAC system don't often have thew push buttons, and if they do, it's worked into the system so that the lights remained calibrated... BUT this might take a few signal cycles to get back into "the loop."


Also, flashing your lights does not effective the signals in Los Angeles. If any sensor exists that controls the signal, it's in the ground behind the crosswalk line. (Those visible in the above picture as loops are counting traffic, not controlling the signal). The weight of a vehicle will trigger the signal to change, so driving over it multiple times does not help - you must let it sit long enough to trigger. True, some of these sensors are sensitive and only trigger when the vehicle is in the exact spot. Sometimes backing up to reposition will work, but it really has nothing to do with the back and forth driving over the sensor.

photo via slimdandy at Flickr

10 comments:

Zach Behrens said...

But in Santa Clarita, flashing your lights at most major intersections in the middle of the night when you are stuck at an intersection alone will get you where you are going faster. All those lights with the little tiny cameras are the ones that will work.

Alex said...

I'm pretty sure those sensor loops are Hall-effect devices that use inductance and sense the proximity of large amounts of metal, not pressure sensors.

solmssen said...

Pressure sensors haven't been used for a quite a long time. There's an example of one at the foot of Ocean Way where it crosses Entrada/West Channel in Santa Monica Canyon - it's a large plate about a foot wide across the lane before the stop line. All lights now use the loop triggers like Alexander says, and moving back and forth across them can definitely trigger the light cycle.

Anonymous said...

I like to hit it twice, just so I feel more proactive.

Anonymous said...

Those loops are definitely metal detectors. Sometimes they are not correctly calibrated for motorcycles and I've had to get off my motorcycle and go and press the pedestrian crosswalk button to get the light to cycle (especially at night when the lights are on a different program). Sometimes placing my side-stand directly on the line in the pavement will trip the lights too.

I've often wondered what the large loop that is in the middle of some intersections is for. I suspect it is to detect imminent gridlock caused by stationary vehicles in the middle of the intersection.

Nate said...
This comment has been removed by the author.
Nate said...

Any tips on how to trip those things on a bicycle? Cicle.org, I think, linked to something about how I ought to lay my bike on it so the sensor can get a "whiff" of the metal. But that doesn't seem to work.

Anonymous said...

I don't think those loops are actually metal detectors, but rather they detect electromagnetic energy running through your car. allegedly the amount of electricity running through a motorcycle is not enough to trigger the sensors and change the non-timer lights in the middle of the night. I've heard cutting and restarting the ignition on a motorcycle helps. sometimes late at night at the one really ornery intersection near my apartment, I rev the engine on my honda 750 nighthawk nerd-o-cycle really high just once and the light seems to change soon after, whereas if I sit there with the engine idling it could be two or three minutes before I have to get off my bike and hit the walk signal. or I just run the red light.

Anonymous said...

Hehe... "nerd-o-cycle" :)

Thanks for the tip, I'll give it a try. Although I'll be careful about reving my aftermarket pipes too loudly, I normally try to keep the noise down late at night.

Sahra Bogado said...

When I am riding my fast bike (it's lightweight aluminium), I couldn't get the metal detector loops to recognize me either.

Then someone showed me how to get things done:

(1) Stop you bike off to one side of the magnetic loop

(2) If that doesn't work, tilt you bicycle over a bit (to get it closer to the ground) in a spot off to one side of the sensor.

Or, you can do like this one engineer I know suggested - put a huge magnet on the bottom of your foot and swipe it at the thing when you're at a stop light (not recommended).