Comment by toast0

You've got the capital costs of having the several lights, built for 24/7 operation, plus the traffic controller. Then you've got to wire that up, and get an electrical connection for the controller box. Plus all the cuts in the pavement for vehicle detectors. Additionally the pedestrian intend to cross buttons and accessibility indicators for pedestrians. And you may need to resurface before or after, and redraw the lines. Likely you'll need signs. Possibly any other curb work that had been neglected, but needs to be done on a new project.

Plus it costs money to do the traffic survey and analysis to decide if you wanted to build the thing in the first place, and to determine the cycle timings. If you need to run an environmental impact report, that's more money on analysis.

Here's some estimates for component prices https://wbt.dot.state.fl.us/ois/tsmo/TrafficSignalBudgetingC... which I don't think includes installation. Probably $50k to $100k for the hardware, but there's a lot of labor, and engineering time.