Real-world graph problems



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Posted by: stak
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Posted on: 2011-09-30 10:01:46

I've spent a bunch of time over the last few weeks walking and biking around downtown Toronto, and it seems to me that the whole "right-turns-only is more efficient" argument doesn't apply here. Whenever cars want to make a right turn in Toronto, they end up having to wait an absurdly long time for pedestrians to finish crossing. Also the right lanes on most streets are filled with all manner of parked cars and service vehicles, so anybody wanting to stay in the right lane needs to keep merging in and out of the left lane to avoid these obstacles.

Given the gridlike arrangement of the streets, it seems to me that the most efficient route between any two points would involve exactly one turn, which would ideally be a left turn at an intersection with an advance green. In practice you'd probably need multiple turns to avoid going down one-way streets the wrong way. Also avoiding streets which have streetcars but not a dedicated streetcar lane is a good idea, since cars have to stop for streetcars that are loading/unloading passengers, and this causes traffic to back up.

I wonder if UPS/FedEx take these things into account when they plan their delivery routes...

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