Why will traffic lights give right of way to EMS vehicles in Chicago Suburbs but not Chicago?


Grew up in the suburbs and have grown accustomed to the strobe light sensors that sit atop traffic lights. They’re incredibly useful for sensing oncoming emergency vehicles, and usually activate the traffic light to stop traffic and give EMS the right of way.

I’ve noticed when driving in the city of Chicago on roadways near, let’s say, the Argonne Ballroom or lakeshore drive, these were not present.

What’s the deal?

In: 9

Those systems cost thousands of dollars per intersection. And Chicago has a lot of traffic signals.

As stated, could be a cost issue.

The emergency departments in that area may not have the systems installed on their vehicles, so there’s no point installing them on the signals.

I don’t know Chicago at all, but if the area you describe is a different city that’s within the overall Chicago area, that public works department can have a different approach to traffic management.

I do not have any specific knowledge of Chicago, but my hypothesis would be that it is related to how the traffic lights are controlled.

In the suburbs where the traffic is light or there are fewer junctions each set of lights can be considered as an enclosed system – whatever method they use to decide when to change the lights (timers, sensors) are calibrated to suit that one junction and that’s it. If an ambulance overrides the system that’s fine as they don’t consider any knock on effects.

Traffic lights in a city are calibrated (or controlled) to take into account not just the set of lights at one junction, but all of the junctions around it. You can see this when sometimes you can drive across town and every light is on green, but catch a bad light and they’re all on red. A lot of thought goes into getting this right. An ambulance overriding one set of lights could have a knock on effect that gridlocks an entire city.

Having all of the lights centrally controlled by a computer which can make changes on the fly could facilitate this, but new infrastructure costs money.