Wednesday, August 29, 2012

"One simply does not drive in to Mordor"

, says Lileks of the twincities' discouragement of vehicular efficiency.


big update:

as a slight tangent to that article, the comments began to discuss whether or not repurposing lanes from auto to bike traffic adds to traffic congestion - to which the obvious answer is "obviously". but one commenter took the "pious bicyclist" attitude, which eventually included the claim that:
On urban streets, lane reductions in themselves almost never affect capacity, congestion, or level of service - it's the higher-volume intersections that control how well vehicles can get through (green time doesn't grow on trees).
to which i replied (snarkily i'll admit):
"lane reductions in themselves almost never affect capacity" - seriously??? replace the water and sewer lines at your house with quarter-inch pipe and tell us how that works for you...
some hours later he replied with:
Fluid molecules and drivers are not the same. Fluid molecules are much more predictable. Fluid molecules do not drink, text, or become distracted, and do not have $500 collision deductibles.

A very common early assignment in college introductory-level transportation courses is for students to analyze the capacity of an urban street - first, by analyzing the capacity of the roadway between intersections (usually high), and then by analyzing the throughput at intersections (much lower unless there are many lanes or unbalanced phasing). It's a great way to get it through the students' heads that things aren't always as they initially seem, and that analogies to other flow concepts don't always hold up.
, which is partially true but sidesteps the issue.

(i would have added my rebuttal at lileks' site, but it seems to disable additional comments for previous days.)

the whole bit about fluid molecules is true, and it's true that things aren't always as they initially seem. but even simple geometry dictates that fewer lanes hold fewer cars. if his claims were true, no road would need to be more than a two-way path. if "capacity" and "number of lanes" have no connection, then the "capacity" of the katy freeway out of houston is the same as fm2092 out of menard. And if more lanes do not mean more cars, then all highway expansion projects are pointless as they do not allow more cars on the road.


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