Re:Drone footage of Seattle's new 57 foot SR 99 tunnel [video]
by mulmen on Monday October 23, 2017 @09:16PM
(#15538409)
Fine points but in this case posted MPH isn't an output, it's an input. So is the number of lanes.
Spacing is a function of speed. Even with autonomous cars spacing is not constant because there are on and off ramps so some will be accelerating or decelerating. We don't even know how those cars will work, maybe you can pay more to drive faster!
The question here is which configuration of the tunnel will maximize throughput.
I can't find any explicit statement of the planned speed limit but I did find a document [1] that implies there will be variable speed limits much like other highways in the area.
[1]: http://www.wsdot.wa.gov/Projects/Viaduct/Media/Default/-NewD...
If the spacing of the cars is the same between the two, then a 60 mph lane is moving more cars per second than a 40 mph lane. The spacing never is the same, though, unless these are autonomous cars.
Also, throughput is limited by bottlenecks. If an upstream bottleneck has throttled things to one car every ten seconds, it doesn't matter whether the downstream lane is 30 mph or 60 mph.