3 ms·

Funny you mention that metric since it happens often and is irrelevant since throughput would be way more interesting since it is often chosen as a metric to "s

by consp 4y ago

Funny you mention that metric since it happens often and is irrelevant since throughput would be way more interesting since it is often chosen as a metric to "solve" congestion, especially total throughput (including not cars) would most likely increase the total speed (in general) for all commuters due to limiting congestion. Don't mention to car-centric politicians the most effective speed for safe throughput is about 40kph/25mph and not 120/75.

eru 4y ago
> Don't mention to car-centric politicians the most effective speed for safe throughput is about 40kph/25mph and not 120/75. I would assume that depends on the road in question? Eg Autobahn vs dirt road? If not, that would be a very interesting result!
- consp 4y ago
  Throughput is mostly independent of road as distances between cars increase more than you can speed up to compensate (you reaction time stays the same or get's worse). Type of road can make a difference, obviously dirt makes the distance requirements worse. If people also exit/enter the road it's even worse. I was assuming an ideal road though with everyone sticking to the same speed. Cross lane movement and speed difference in traffic also places limits and slower speeds limit both of those afaik.
- wiredfool 4y ago
  It's pretty well known graph in traffic engineering -- Max throughput isn't free flowing traffic. (Though I remember it at 35-40 mph on interstate/motorway). The basic reason is that free flowing traffic requires bigger gaps between vehicles. (safe anyway, but practically the way people drive generally follows the safe spacing function, but with a 'bit' of y offset). At the minimum latency (the free flow speed (ffs)) the spacing between cars is x seconds, so you get 3600/x cars per hour. At maximum flow rate, ~1/2 the ffs, the spacing is more like 1-2 seconds, so you get closer to 2k cars per hour. Even slower, the cars can be packed closer, but you don't clear the road nearly as quickly so the throughput is lower. See https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd1.pdf https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd... (page 13) and https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd2.pdf https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd... (page 9) It's a little bit like the tradeoff between latency and throughput in servers.

by consp 4y ago

eru 4y ago

> Don't mention to car-centric politicians the most effective speed for safe throughput is about 40kph/25mph and not 120/75. I would assume that depends on the road in question? Eg Autobahn vs dirt road? If not, that would be a very interesting result!

consp 4y ago
Throughput is mostly independent of road as distances between cars increase more than you can speed up to compensate (you reaction time stays the same or get's worse). Type of road can make a difference, obviously dirt makes the distance requirements worse. If people also exit/enter the road it's even worse. I was assuming an ideal road though with everyone sticking to the same speed. Cross lane movement and speed difference in traffic also places limits and slower speeds limit both of those afaik.
wiredfool 4y ago
It's pretty well known graph in traffic engineering -- Max throughput isn't free flowing traffic. (Though I remember it at 35-40 mph on interstate/motorway). The basic reason is that free flowing traffic requires bigger gaps between vehicles. (safe anyway, but practically the way people drive generally follows the safe spacing function, but with a 'bit' of y offset). At the minimum latency (the free flow speed (ffs)) the spacing between cars is x seconds, so you get 3600/x cars per hour. At maximum flow rate, ~1/2 the ffs, the spacing is more like 1-2 seconds, so you get closer to 2k cars per hour. Even slower, the cars can be packed closer, but you don't clear the road nearly as quickly so the throughput is lower. See https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd1.pdf https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd... (page 13) and https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd2.pdf https://courses.washington.edu/cee320ag/Lecture/Freeway_LOSd... (page 9) It's a little bit like the tradeoff between latency and throughput in servers.