3 ms·
>> The capacity of a sufficiently long road section does not increase with speed Most roads aren't sufficiently long and there's plenty of other factors and pr
by CraigJPerry 6y ago
>> The capacity of a sufficiently long road section does not increase with speed
Most roads aren't sufficiently long and there's plenty of other factors and practical road usage is nowhere near this perfect maximum of safe usage but to point out your mathematical error:
For 10 minutes a section of road 1 mile long has traffic pass through it. The cars have 3 second gaps between them.
At 30 mph: 160 cars max throughput
At 60 mph: 180 cars max throughput
In the 30mph example, for the first 2 minutes, 0 cars have completed the 1 mile stretch, for the period 2-10 mins, cars pass the finishing line every 3 seconds. 160 cars complete the 1 mile stretch in 10 mins.
In the 60mph example, only the 1st minute is spent without traffic completing the throughput analysis. For the period 1-10 mins, cars pass the finishing line every 3 seconds. 180 cars complete the 1 mile stretch in 10 mins.
- yholio 6y agoYes, you need to double the speed and construct an artificial trafic burst to notice a marginal increase in capacity that is strictly due to the increased delay (and storage capacity) of the slower road. That was my point. In practice trafic ramps up slow enough so that we can ignore the lost capacity due to empty roads in the early hours. After that, it is steady state for both scenarios. > there's plenty of other factors and practical road usage is nowhere near this perfect maximum of safe usage Precisely, but this even further argues against high speed limits. If the road tends to be congested, windy, has trafic lights and is poorly maintained, the areas where you can increase the speeds are very limited and the total impact in trip time is low. So high speeds not only not deliver higher throughputs but they fail to even deliver speed.