25 ms·

I've always wondered why those cabinets are so big. Traffic light controls seem like the kind of thing that could be reduced to a much smaller package given gre

I've always wondered why those cabinets are so big. Traffic light controls seem like the kind of thing that could be reduced to a much smaller package given greater computing power combined with smaller and more efficient hardware. What does all the hardware inside actually do?

ams6110 8y ago
probably sized to house standard rack-mount gear.
greenyoda 8y ago
Maybe one box needs to communicate with a network of other boxes to keep traffic in sync over a wider area. I'm guessing that the bottom rack with the yellow cables plugged into it is some kind of networking gear. Also, the equipment has to switch some fairly high-power loads - until the recent adoption of LED-based traffic lights, I'd guess that traffic light bulbs probably drew a few hundred watts each, and there can be many lights in a large intersection. You can see a row of 15A and 20A circuit breakers in the box in the photo, on the left side of the second rack from the top, with a 50A main breaker below them. The equipment below that rack looks like power-switching modules. It's also entirely possible that this equipment is 20 or 30 years old, built at a time when computer hardware was much bulkier. There would be little incentive to replace it with something smaller if it was still working reliably.
- AstralStorm 8y ago
  In fact, this being repairable in the field by a person with a soldering iron and a bag of parts is a consideration. Sometimes you cannot just get a full module to swap.
  - _jal 8y ago
    This. Repairability and durability are two reasons a lot of 'old tech' is in use. I have a friend who is an engineer with PG&E who is great to take to parties full of tech nerds. They're always horrified by the '100 year old tech' running the grid. My take is that they're right to be horrified by the fragility of the grid, but have the 'why' exactly backwards - it isn't the vats of oil that make it fragile.
- ams6110 8y ago
  IIRC, in some cities (Chicago for one) there is a radio broadcast timing signal for traffic lights. There is a receiver in each control box. Sort of a WiFi NTP for traffic signals. Probably totally insecure and subject to hacking also.
nwahs_kc 8y ago
A previous post was correct. There width is a standard rackmount in 332-type cabinets. The 332 type cabinets were originally designed by the California Department of Transportation. A lot of the design of cabinet dates back to the 70's. Until just recently the industry started to look at shrinking things down. Going to LED signal indications has helped a lot. The devices used to convert the low voltage coming from the traffic signal controller to switch to the high voltage driving the old incandescent heads took up a bit of space. How you land all the wires from signals heads and sensors also takes up a bit of space. Some day when we have connected vehicles, vehicles talking directly to the signal cabinet we should be able to shrink things down even more.
- HeyLaughingBoy 8y ago
  How you land all the wires from signals heads and sensors also takes up a bit of space That's what I figured the most likely answer to be. Simply connecting one wire to another (in a manner that makes repair/replacement easier) can take up a surprising amount of space and most control panels have rows of terminals that exist just for that purpose.

ams6110 8y ago

probably sized to house standard rack-mount gear.

greenyoda 8y ago

Maybe one box needs to communicate with a network of other boxes to keep traffic in sync over a wider area. I'm guessing that the bottom rack with the yellow cables plugged into it is some kind of networking gear. Also, the equipment has to switch some fairly high-power loads - until the recent adoption of LED-based traffic lights, I'd guess that traffic light bulbs probably drew a few hundred watts each, and there can be many lights in a large intersection. You can see a row of 15A and 20A circuit breakers in the box in the photo, on the left side of the second rack from the top, with a 50A main breaker below them. The equipment below that rack looks like power-switching modules. It's also entirely possible that this equipment is 20 or 30 years old, built at a time when computer hardware was much bulkier. There would be little incentive to replace it with something smaller if it was still working reliably.

AstralStorm 8y ago
In fact, this being repairable in the field by a person with a soldering iron and a bag of parts is a consideration. Sometimes you cannot just get a full module to swap.
- _jal 8y ago
  This. Repairability and durability are two reasons a lot of 'old tech' is in use. I have a friend who is an engineer with PG&E who is great to take to parties full of tech nerds. They're always horrified by the '100 year old tech' running the grid. My take is that they're right to be horrified by the fragility of the grid, but have the 'why' exactly backwards - it isn't the vats of oil that make it fragile.
ams6110 8y ago
IIRC, in some cities (Chicago for one) there is a radio broadcast timing signal for traffic lights. There is a receiver in each control box. Sort of a WiFi NTP for traffic signals. Probably totally insecure and subject to hacking also.

nwahs_kc 8y ago

A previous post was correct. There width is a standard rackmount in 332-type cabinets. The 332 type cabinets were originally designed by the California Department of Transportation. A lot of the design of cabinet dates back to the 70's. Until just recently the industry started to look at shrinking things down. Going to LED signal indications has helped a lot. The devices used to convert the low voltage coming from the traffic signal controller to switch to the high voltage driving the old incandescent heads took up a bit of space. How you land all the wires from signals heads and sensors also takes up a bit of space. Some day when we have connected vehicles, vehicles talking directly to the signal cabinet we should be able to shrink things down even more.

HeyLaughingBoy 8y ago
How you land all the wires from signals heads and sensors also takes up a bit of space That's what I figured the most likely answer to be. Simply connecting one wire to another (in a manner that makes repair/replacement easier) can take up a surprising amount of space and most control panels have rows of terminals that exist just for that purpose.