Biker trapped in parking garage

January 10, 2006 8:09 AM

How do automatic gates in parking garages work?

I sometimes ride a motorcycle to work. A card key opens both the in gate and out gate (when I'm driving my car, that is), but some kind of sensor needs to trip the card slot to suck my card in, which in turn activates the gate. Strangely, I can get through the in-gate on my bike, but not the out gate! The parking attendant has no long-term solution for me and the parking office couldn't care less about me and my problems. I guess my question is: Is there an electric eye involved, or is it something like those underground "trippers" like the ones that trigger certain traffic lights? And, if it's the latter, do any MeFi bikers know if a Green Light Trigger will work in this situation?

posted by scratch to travel & transportation (8 comments total)

At the parking lot at my college it was magnetic induction loop sensors buried in the ground - I believe this is fairly common. We could trip those sensors with a Club (locking device) held parallel to the gate on one of the cut lines in the asphalt - if there's enough room try turning your bike at a 45 degree or more angle and see if that trips it. This seems to adress roughly what you are talking about.
posted by true at 8:18 AM on January 10, 2006

...Or you can ride the bike around the gate as you flip off those who don't care about you and your problem.
posted by Makebusy7 at 8:23 AM on January 10, 2006

If you can figure out where the outline of the loop is exactly try riding directly along one side of the loop (trial and error may let you figure this out too). This is how I used to be able to trip traffic signal lights on my bicycle. It is usually easy to see the outlines in ashpalt because they cut a patch to install the loop. If your parking garage uses concrete it might not be so obvious.
posted by Mitheral at 8:55 AM on January 10, 2006

Had the same problem at my apartment with a tiny sports car. There was a ~three foot piece of metal just inside the gate that we sometimes had to drag over the concrete to get the gate to activate. You may end up finding having a portable piece of metal stashed somewhere near the entrance is easier than moving your bike around trying to find the sweet spot.
posted by user92371 at 9:20 AM on January 10, 2006

I install these sorts of gates all the time for carwashes.You could ask the parking lot's maintenance/service crew to bump up the frequency of the gate - if they have a key to the post that the gate arm hangs off of, inside there's sensitivity and frequency switches.
The loop sensor everyone's talking about (sometimes cast into the concrete, ergo, no cut lines in the pavement) has a pair of twisted wires running around a roughly 2'x4' loop. It senses metal (obviously)via the change in the induction of the wires when something metallic nears its magnetic field. If they don't want to up the sensitivity, figure out where the loop is, then use a ~3' piece of cast iron pipe and cross the loop - from the midpoint of one side to the midpoint of the other side. Roll the pipe a little bit, and you should be golden. It'll be a bitch to carry, but...[for the record, the aboveground loops we use to sense car length can be set off using metallic conduit.]
posted by notsnot at 9:42 AM on January 10, 2006

My motorcycle-driving brother asked me to post this suggestion: use a traffic light trigger. It's a magnet to place on the bottom of your bike which will trip a traffic sensor.

Can't guarantee how well it works since I've not used it (or driven a motorcycle)...
posted by bCat at 12:25 PM on January 10, 2006

... re-reading your initial comment and my post above (along with my brother's cryptic e-mail), I should have written that he has successfully used light triggers in parking garages.
posted by bCat at 12:35 PM on January 10, 2006

Thanks all. I'm not sure I'll be able to schlep around a 3-foot piece of cast iron pipe without being arrested on suspicion of something or other, but I'll try one of those magnetic triggers for sure.
posted by scratch at 4:28 PM on January 10, 2006