Not to quibble with all the frustrated physicists, but magnets may react to aluminum, copper, kryptonite or unobtanium. Non-ferrous bikes often don't trigger traffic sensors. That's the point of the thread. I'd be thrilled to read about capacitors and floating aluminum disks in a science forum -- heck, I like science -- but that's neither germaine nor interesting to the folks who come to this forum to exhange information about (brace yourself) bicycles.

If you care to explain, referencing the appropriate physics, how an inductive loop detector works and why it will not respond to a non-ferrous metal, I'm all ears (eyes).

Otherwise we have it on the authority of a EE that they work just fine with aluminum, there's nothing special about steel or magnets other than the fact that they conduct electricity. I've provided real-world hands-on examples of how non-ferrous metals can interact with a magnetic field (and all detection of any kind is premised on interaction--if you can interact, you can detect). Or perhaps we shouldn't make reference to wheels, levers, or any of the other simple machines that seem to frequently play a roll in the world of cycling because that's science, not bikin'!

So what's the deal? How is it that aluminum doesn't doesn't trigger the detector apart from the fact that the detector is simply misadjusted. Sometimes my very ferrous rides don't trigger them either.

Thanks, Steve, for the link to your article. I think it will be great help for anyone petitioning localities to alter their detection systems.

(And, as I'm a physicist, it was fun to read!)

It depends on where you are relative to the most sensitive part of the loop and to how sensitive the loop has been set by traffic engineers. Some loops have been desensitized because of heavy (volume) or heavy (size) cross traffic. Try to ride straight down the middle of quadrapole type sensors (the figure 8 kind). For dipole type, ride straight down the wire on either side (these are much harder to trip). This assumes that you can see the wire cuts in the pavement. If you can't see them, it's a bit like playing Battleship :D You just hope you hit it right.

Or you may be running across the more frequently used, but still uncommon, motion detection sensor. If the traffic lights have what looks like little telescopes on each pole, it's probably a motion detector. I only have a couple of these on my routes but they can be a bugger to get tripped. I finded that if I do a little left (or right) hook just as I get to the light, I become a bigger target and the light will trip.

I found it is good to find the individual who is responsible for making sure sensors are tuned right and develop a friendly relationship with them. If you don't get response, they letters to city leaders are appropriate. But you want to be able to report improperly tuned sensors as you find them, which is why knowing the best individuals to contact is important.

I don't like buttons off to the the side of the road for cyclists to push. We have them here and they mean you must scurry up to the edge of the sidewalk which is a horrible place to be for left turns and going straight. Also once a button for cyclists is in place it takes away the responsibility for the sensors to work for bikes (as I have disapointingly learned)

Al

I think it would be great if there was an LED on the lightpost box that turned on when the light is triggered. Round here there can be a many minute delay after a light is triggered and when on a bike its hard to know if you've done it or not.

The LED should help drivers and public work dept. too.

Al

Not only that, but they can be physically difficult to reach (say if it's snowed recently) and can make it difficult to reenter the traffic flow. Not only that, but once you have gone over there, you've pretty much surrendered your right of way.

Scott:
Getting a public works employee to adjust an inductive loop detector to sense an alloy rim is a political/legal challenge, not a technical problem. It is great that you took the initiative to write to your public works department and copy your elected officials. Unfortunately, few bicyclists know how effectively advocate for change.

The East Bay Bicycle Coalition assists such grassroots activism throughout 33 cities in two San Francisco Bay counties. East Bay bicyclists frustrated with unresponsive signals, or other hazards, fill out an on-line Hazard Report Form and the EBBC sends it to the correct jurisdiction along with a notice of legal liability. We retain records of such reports and follow-up to insure that they are responded to. This process is extremely effective because: 1) we contact the right people; 2) we remind them of your legal standing; and 3) united in a coalition of bicyclists, we have political clout.

Stuart:

I must say, I think you are wrong about the City of Denver. The city has a policy that it will not adjust the detector loops for bikes. Even the latest lights malfunction in this fashion. A good example: Stapleton's new lights don't work.

Obviously, if there is a car present, as there often is if you are commuting during regular hours on roads full of cars, the detectors are not a problem. Also about half the lights are timed.

Denver doesn't have a policy against adjusting detector loops that I am aware of. Denver has been very progressive on bicycle use. It may just be a problem with a particular light. Contact the city bicycle planner. He may be able to help.

Well, if you would be kind enough to give the city bicycle planner a call, you could start with these intersections:

23rd & Syracuse
26th & Quebec
Montview & Colorado
17th & Steele
St Paul & 1st Ave
E. Ellsworth & Cherry Creek
E. Bayaud & Cherry Creek

Thanks.

Where I live you need to be very specific - just an intersection name is not enough. Which lane and which road & direction is needed and what time of day.
Al

My experience is that in Denver that's not needed, because the city simply says "no." But I'm hoping Stuart knows whom to call and will have more success than I have had.

Call Signal Repair 720-865-4000. Be personable and get names.

Also get to know:
James Mackay
Bicycle Coordinator
720-865-BIKE (2453)
James.Mackay@ci.denver.co.us

And let him know of your traffic signal issues.

Al

Thanks for the information.

The folks who answer the phone - quite nice - have never received a call about bicycles. They referred me to an engineer - also quite nice - who relates that Denver adjusts loops in bike lanes but nowhere else. Perhaps Stuart can do better.

I know you meant this well, but this is not someone I would call. He is an oldtimer at the city. He probably also means well. Nonetheless, the new lights installed at Stapleton just this year still malfunction (and a significant number of Denver's bike routes use sidewalks.)

Hey I'm glad you tried. I can understand the logic (but disagree) of not adjusting a loop if there is an adjacent bike lane with a loop. But what if there is no bike lane? What about left turn lanes where triggering with a bike is very important. I'd say you Dever folks need to do some advocacy. A policy of having intersections that do not function properly for bicycles should be changed.

Al

One more addition to the Denver list! If you know whom to call in Denver to get something done, you might also mention the lights that stay red until a car approaches doing below the speed limit (plus a few mph.) They may be called "rest on red." Those lights, like the loop actuated signals, don't detect bikes. A responsible cyclist, obeying the signal, ends up stopping at an empty intersection until a car approaches. The one on Montview around Elm would be a good example.)

(That light is a good example because, ironically, Montview is one of the small number of Denver streets with a bike lane. It may be the only bike lane in Denver that allows room for the "door zone." The new lanes at Stapleton don't. They allow no margin for an open door or even for a wide SUV. In addition, at least a couple of the recently designed and approved Stapleton lanes run riders directly into protruding curbs!)

The lights are good to slow cars down but indicative of Denver's approach to bikes, i.e. bikes belong on paths or sidewalks but not on the road. Speer Boulevard is the future of Denver bicycling: Bikes prohibited; use the sidewalk, press the pedestrian button, and show up once a year for Bike to Work day.

Vancouver and its suburbs have started installing a lot of these. On my morning commute thu New Westminster i go thru about 5 of these. They are mostly on side streets labeled as bike routes crossing a busy main street. They are placed on the right hand curb, right at the edge nearest the street, with the button facing the street. No need to get off the bike to press it. (most people i see using them stay clipped in and use the post to hold themselves up till safe to go.

The ones i activate daily work on what seems to be about 5 second delay. There isnt even enough time to take a drink before the light switches after pressing them. Very fast, rarely have to unclip, and no time to cool off waiting like slow ones.

I agree they dont work on multi lane roads since on those we need to be in lanes other than the curb lane to turn, etc. But for the situations I described above i find them working quite well.