No they don't. I'm not sure where they got that number from, but it's either wrong or being misrepresented (costs of entire infrastructure project confused with cost of lights). $10M is off by 1-3 orders of magnitude, depending on if you're counting installation of just one signal or a complete intersection.

It's conceivable for the installation of traffic lights in a remote place to be an expensive project if there's no power available there, but that's a much larger project than just a single traffic light.