[Mister_Snuggles]

This already happens in some cities. There are traffic lights in my city, for example, which adjust for trains, presence of cross-traffic, etc. The cross-traffic one is neat because a light will, quite literally, stay red forever and only change when a car pulls up to actually use the green light.

From this[0] article:

> Today, cities use computer-controlled traffic lights that adjust their timing based on traffic levels, the time of day and even the number of trucks on the road. In Los Angeles, for example, city officials use traffic management to control their 4,400 traffic lights, reducing travel time by 12 percent.

[0] http://www.foxnews.com/tech/2014/08/05/high-tech-traffic-lig...

[wlesieutre]

My hometown had one of those "cross-traffic" lights a few blocks from my house at an intersection that I had to cross to reach one of the major bike paths.

Naturally, it didn't register bikes. So if you wanted the light to ever change, you had to cross over to the left side of the street, go up on the sidewalk, and push the pedestrian button (no crosswalk on the right side of the intersection). Not much of a fan.

I'm not saying they're always bad, but they're not always good either. Maybe newer ones have improved on detection, but my understanding was that the sensor was induction based and required a big chunk of metal in order to spot you.

[ericfranklin]

I've seen the induction loops "presence" sensors too. One near where I used to live would never change to green unless the sensor was triggered, but wouldn't register until your car was beyond the crosswalk, nearly in the intersection. That means if someone in front of you stopped where they were supposed to, the light would never change.

I suppose there is bias though, in that people don't notice as much when traffic lights are operating efficiently.

[maxerickson]

If the sensor there is an induction loop you might be able to figure out where it is and line a wheel up well enough that the metal rim triggers it.

[wlesieutre]

I was never able to, but I didn't do a careful search for it. If only every city used that same bike icon to show you where the sensor is.

[fredophile]

Probably not. From my experience bicycles and small motorcycles will not trigger the sensor on the induction loop.

[maxerickson]

I looked around some before I posted that. This article seems respectable enough and at least supports the idea that bikes are intended to be able to trigger some of them:

http://bikeportland.org/2010/09/27/bike-science-making-sense...

[fredophile]

It looks like those are specifically designed to be triggered by bikes. I've been at intersections with a 50-100cc motorcycle that would not trigger the light.

[maxerickson]

I have the idea that they are broadly intended to work for bikes and the like but that they aren't always installed or tuned correctly.

[fredophile]

In my area I find that the cross-traffic ones are poorly implemented. I'll drive up, come to a complete stop, the light will change for me and will already be back to yellow before I clear the intersection. This forces me to always stop when there was no traffic on the preferred route. It also means that if there is a car more than a few car lengths ahead of me it will change for them and force me to wait a full cycle even when there isn't traffic on the preferred route.

This shouldn't be a hard problem to fix. Sensors just need to be installed farther from the light to detect approaching vehicles earlier.