Portugal's Velocidade Controlada -- speed control traffic signals
Recently I did a road trip through Portugal. I always enjoy finding something new that they are doing in a country which has not yet spread to the rest of the world.
Along a number of Portuguese roads, you will see a sign marked "velocidade controlada" -- speed control -- and then a modest distance down the road will be a traffic light in the middle of nowhere. There is no cross street. This is an interesting alternative to the speed bump or other "traffic calming" systems.
At the sign a radar gun measures your speed. If you are over the limit, then as you approach the light, it turns red. It turns red for you, and also anybody behind you and the oncoming traffic.
The result is people slow down for these signs to the limit. Far more effectively than any speed bump, and without the very annoying bump. Mostly this is done on faster roads than the quiet residential streets that have speed bumps, and of course traffic lights cost more than speed bumps, at least today.
The social dynamic is interesting. Even though many of us are scofflaws when it comes to the speed limit, most are much more religious about a red light. Even a red light like this one where there is no physical danger to running the red light, just the fairly unlikely risk of a stronger ticket. Strangely, though both speeding and running this light are both just violations of the law, I never saw anybody run one, and drivers who were total speed demons elsewhere quickly slowed down before these signs. (People know where they are, so they aren't a general speed reducer, but rather more like a speed bump in cutting speed in one particular place.)
Added to this is the element of public shame. If you trigger this light, you stop everybody around you too. If you're a sociopath, this won't concern you, but for most there is a deep shame about it.
Today, as noted, a traffic light and radar gun are a moderately expensive thing. These lights are not nearly as expensive because they don't require the complex intersection survey and programming of sometimes 20-30 real lights, but they still need a pole, and electricity, and weather hardened gear. In the future, I predict this sort of tech will get quite inexpensive, possibly cheaper than a speed bump. You could imagine making one with solar power and LEDs which only displayed the red light, not the green, and so needed no external power for it. They need not be on all the time -- in fact if the batteries got low, they could just shut down until they recharged. The radar and communications link could also become quite cheap.
Of course, I would like to see this combined with more reasonable speed limits. I have pointed out before that the French Autoroute approach of a realistic limit of 130km/h that everybody obeys and where you really get tickets if you exceed it is much better than the US approach of a 65mph limit that 90% of drivers disregard. This system is much better than the speed bump. Speed bumps hurt cars and impede emergency vehicles. Emergency vehicles can blow through these. These could even vary their speed based on conditions and time of day.
Robocars of course would know where all these are and never trigger one, even if the occupants have commanded the vehicle to exceed the limit. But this is mostly a technology for human drivers. It is halfway along the path to "virtual infrastructure," which is how roads and traffic control will work in the future when every car, human driven or not, uses a maps and data over phones to know the road, rather than signs and lights.