[tren-hard]

Also worth noting that just about every redlight intersection has cameras mounted on top pointing at traffic in each direction.

It's pretty much impossible to navigate through a city anonymously in a vehicle.

Now with facial recognition software getting so advanced I'd water it's impossible to walk through a city anonymously as well.

They don't necessarily need aerial imagery when every intersection has HD cameras pointing at you.

[lotsofpulp]

They’re not cameras, they are metal/RF/infrared/whatever detectors used to detect vehicles waiting at the intersection so lights don’t stop traffic for no reason.

Source: I’ve had to call municipal governments to get the detectors rotated or angled properly due to them not detecting cars and therefore not changing the light to green.

Of course it’s technically possible they also contain cameras, but I have yet to see any proof.

[Animats]

Traffic signal cameras for traffic light control are common. They used to be dumb monochrome analog cameras connected to simple "non-pavement object detected in box" processing units. There's been considerable mission creep since. Here's the promo video from Econolite's current product.[1] HTDV, WiFi, car, truck, bus, bicycle and pedestrian detection, connects to control center if the bandwidth is available.

CALTRANS has most of their highway cameras available from their web site.[2][3] CALTRANS has been at this since the 1980s, and the cameras are mostly somewhat old and low-rez.

[1] https://www.econolite.com/products/detection/autoscope-visio...

[2] http://cwwp2.dot.ca.gov/vm/streamlist.htm

[3] http://cwwp2.dot.ca.gov/vm/iframemap.htm

[kube-system]

Yes, optical detectors are often used for traffic control.

Traffic cameras which stream visible-light video are also very common. https://www.weatherbug.com/traffic-cam/

[catalogia]

I'm not sure why you've been downvoted. Traffic-aware traffic lights are generally implemented using induction loops built into the road surface: https://en.wikipedia.org/wiki/Induction_loop

Today, many have cameras for other reasons. But this is not ubiquitous and the prevalence of these cameras varies from location to location. Many traffic lights don't have cameras (many don't even have induction loops, and work off timers instead.)

[nucleardog]

In areas where the ground is covered in a foot of snow and ice all year those aren't particularly effective and they do use devices that look kinda like cameras and everyone assumes are cameras.

They're actually just small radar devices. It's a much simpler problem to solve across a wide variety of conditions to simply point radar at the ground and when the distance suddenly drops 4-8' assume a vehicle is there.

These devices don't have any sort of lens assembly which should be your first clue, but they also are pretty easily differentiated if you own a radar detector as well...

[stephen_cagle]

How often is this done? Do they also detect if a bike is at the intersection? Will they eventually cycle the light even if nothing is detected (just in case the sensor is not working)?

[lotsofpulp]

They are at almost every intersection in my state. I’ve heard people in bikes complaining about having hard time getting detected sometimes. I suppose it depends on how the light is programmed if it has a max time before it cycles, but I’ve had to go through intersections on a red light because I waited minutes and it didn’t turn green.

[jcrawfordor]

Video-based lane occupancy detection is widely used by traffic lights, but it's rare for these cameras to be connected to anything other than a trigger module in the signal cabinet. It is conceptually possible to also connect these cameras to a remote monitoring system, but this comes at a very high cost. My city has been one of the stronger proponents of doing so but has only connected a very limited number of intersections due to the expense.

[fapjacks]

The city (major suburb) I used to live in has done this with all the intersections that lead into the city, effectively making it impossible to enter or leave the city without them having a record of it. I know they are able to scan license plates from these cameras -- and do so automatically -- because it's how they are able to "catch" people trying to use those 3M strobe lights that ambulances and fire trucks use to make the lights turn green: An intersection detects the use of the strobe, but also is able to know that no (deployed) emergency vehicle is near that intersection, so it automatically "calls" the police department with the license plate of the offender. This information was buried on that city's website in a bunch of short videos the traffic engineers made about their new gee-whiz traffic management system.

Which, by the way, many municipalities are building (or have already built) "new gee-whiz traffic management systems" which are Orwellian nightmare machines. They seem to be flying well under the radar because everybody hates traffic, and especially because nobody is allowed into the new traffic management buildings for tours, to see the capabilities of the system that seem to be hooked directly into law enforcement's computers.

[jcrawfordor]

Do they directly say that they are using license plate reading? I find it far more likely that they are using the OPTICOM GPS solution which, in hybrid with OPTICOM IR, solves the same problem using cooperative radio equipment in emergency vehicles. Reporting on received IR preemption with no matching radio communication is an advertised feature of this system, whereas performing ALPR at the range and conditions of lane occupancy cameras is still largely experimental. ALPR virtually requires IR illumination, while lane occupancy cameras have no illuminators and are usually monochrome.