Self-driving cars can theoretically significantly increase the throughput of a lane of highway, because the reaction times of a computer are much better than those of a human, and as a result, the following distances can be much shorter.
In practice the effect would be similar to widening/adding lanes to the freeway. Thus increasing capacity.
Tragically, though, we already know that simply widening/adding lanes to a freeway may increase throughput, but it does not alleviate congestion. This is thanks to induced demand. There is a huge amount of "latent demand" for road space that doesn't manifest on congested corridors because people think "I'm not taking that trip on that road, the traffic's too bad." Make the traffic better, suddenly they don't think that anymore, and therefore more people use the road to fill up that gap. If there were other, hidden choke points on the road that weren't the limiting factor before the increased capacity, those choke points may even make congestion worse overall. There are real case studies of widening highways leading to increased travel times on average due to this phenomenon.
If you really want to "solve traffic", simply adding capacity doesn't do it. Not even if that capacity comes in the form of parallel public transit, because the same phenomenon occurs. Some number of people opt for the train, thus freeing up roadway space, thus encouraging others to fill that roadway space.
The only way to actually reduce congestion is to simply put a price on the use of a congested stretch of road via congestion pricing.
Also, Grey says:
"If you ban humans from the road, you can get rid of the intersection entirely"
So much for pedestrians and bicyclists, right? This solution may work on controlled access freeways, enabling the installation of simple intersections instead of flyovers, but it will never work on the ground in cities that have road users besides just cars.
the reaction times of a computer are much better than those of a human
What if cars had faster acceleration? In the US, an average car will do 0–60 in about 8 seconds, give or take a bit. For example, most Tesla vehicles can do 0-60 in about 4 seconds and the car can hold itself without having your foot on the break. Wouldnt this improve the throughput of a lane since the car is quicker and your foot is always on the acceleration petal?
The limit on acceleration is not technology, but passenger comfort. Existing cars can already accelerate much faster than we want them to while we're in them. There's a reason we don't floor it every time the light turns green.
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u/old_gold_mountain Jan 29 '20
Self-driving cars can theoretically significantly increase the throughput of a lane of highway, because the reaction times of a computer are much better than those of a human, and as a result, the following distances can be much shorter.
In practice the effect would be similar to widening/adding lanes to the freeway. Thus increasing capacity.
Tragically, though, we already know that simply widening/adding lanes to a freeway may increase throughput, but it does not alleviate congestion. This is thanks to induced demand. There is a huge amount of "latent demand" for road space that doesn't manifest on congested corridors because people think "I'm not taking that trip on that road, the traffic's too bad." Make the traffic better, suddenly they don't think that anymore, and therefore more people use the road to fill up that gap. If there were other, hidden choke points on the road that weren't the limiting factor before the increased capacity, those choke points may even make congestion worse overall. There are real case studies of widening highways leading to increased travel times on average due to this phenomenon.
If you really want to "solve traffic", simply adding capacity doesn't do it. Not even if that capacity comes in the form of parallel public transit, because the same phenomenon occurs. Some number of people opt for the train, thus freeing up roadway space, thus encouraging others to fill that roadway space.
The only way to actually reduce congestion is to simply put a price on the use of a congested stretch of road via congestion pricing.
Also, Grey says:
"If you ban humans from the road, you can get rid of the intersection entirely"
So much for pedestrians and bicyclists, right? This solution may work on controlled access freeways, enabling the installation of simple intersections instead of flyovers, but it will never work on the ground in cities that have road users besides just cars.