system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do traffic lights cost so much money?

From the Washington State DOT:

"It costs the taxpayer $250,000 to $500,000 to purchase and install a traffic signal. Electric bills and routine maintenance amount to about $8,000 a year."

Thats a ton of money. Or is it?
gpt
The cost includes paying people to examine the area to survey the area, design a plan, purchase the parts, and hire a crew to do the actual installation. The crew will have to dig up existing street to install the detection coils, dig holes for the poles to support the lights, and then repave and clean up everything once it's installed. Each intersection is slightly different, so while there may be some reuse from existing intersections, a lot of work still has to go in to a new installation.