Two cities have found a relatively novel way to reduce high-speed crashes by rewarding law-abiding drivers rather than just punishing the lead-footed ones.
Seriously, also aren’t lights supposed to be programmed to move the most traffic throughout the day… Why would people want to make it less efficient.
Edit: went back and watched the video. They aren’t giving preferred treatment to anyone, they just timed the lights so if you go from 1 to the next it should turn green based on speed/distance. I’m not really sure why you would even need the speed sensors, you can just measure the distance and set them…
This is because at higher speeds, far more safety distance is needed. Because it is dominated by the braking distance, the safety distance increases roughly quadratic with speed. The transport capacity of a steet is however defined by speed divided by safety distance times its lanes. Which means that at higher speed, fewer vehicles per second can pass a point. And small, slow city streets can easily, and safely, transport more vehicles per second than a highway.
That’s also why at an airport, a plane needs a runway with kilometers of free space for a single plane. It is the speed, which requires lots and lots of longitudinal space to retain safe control.
And this is also why bike paths can generally transport far more vehicles per second than streets for cars. For example, Copenhagen has a bicycle bridge that spans the harbour, which is called Cykelslangen. It has only two lanes, and at rush hour times, it transports over two vehicles per second.
I had thought this too, but in the article they mentioned speed sensors that track the speeds of vehicles in one (maybe two?) of these cities. So I think it’s a mix of both of those things, with them probably preferring the preferential approach.
Seriously, also aren’t lights supposed to be programmed to move the most traffic throughout the day… Why would people want to make it less efficient.
Edit: went back and watched the video. They aren’t giving preferred treatment to anyone, they just timed the lights so if you go from 1 to the next it should turn green based on speed/distance. I’m not really sure why you would even need the speed sensors, you can just measure the distance and set them…
Slower speeds are more efficient.
This is because at higher speeds, far more safety distance is needed. Because it is dominated by the braking distance, the safety distance increases roughly quadratic with speed. The transport capacity of a steet is however defined by speed divided by safety distance times its lanes. Which means that at higher speed, fewer vehicles per second can pass a point. And small, slow city streets can easily, and safely, transport more vehicles per second than a highway.
That’s also why at an airport, a plane needs a runway with kilometers of free space for a single plane. It is the speed, which requires lots and lots of longitudinal space to retain safe control.
And this is also why bike paths can generally transport far more vehicles per second than streets for cars. For example, Copenhagen has a bicycle bridge that spans the harbour, which is called Cykelslangen. It has only two lanes, and at rush hour times, it transports over two vehicles per second.
We’ve had this forever. It is called the “green wave”
I had thought this too, but in the article they mentioned speed sensors that track the speeds of vehicles in one (maybe two?) of these cities. So I think it’s a mix of both of those things, with them probably preferring the preferential approach.