By the way, if you are bothered with “costs”, you should be reading what is planned 15 to 20 years down the road. It is called “congestion pricing”. Civil engineers have given up trying to build our way out of traffic congestion. Gas taxes (which substantially pay for new construction) have not kept up with costs for years and the infastructure is declining.
The solution is the force people off the road by making it too expensive for them to use it. It is already used in several places in Europe (and London). When Bloomberg tried it in NYC recently, it was slapped down (this time), but it will keep coming back until the politicians decide it is the right time.
That is the choice. Either build more (with more costs that you actually get something for — a street) or drive people off the road with congestion pricing (which you get nothing for). Which do you think is going to happen in the long run?
They are putting up traffic cameras to make money- not for safety.
The insurance companies and local governments sponsor studies to justify them as it suits their interests. Insurance companies like being able to raise rates on drivers who get tickets and local governments want the money.