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transit and mode share

I've been reading a bunch of kchoze posts the past couple days. This one is on the economics of transit, and transit efficiency.

'if transit is economically inefficient, why are third world cities dominated by transit and not by personal cars? Why do the Japanese pay 10% of their income on transport versus 20% for Americans and Canadians?'

There are some numbers, and discussion of cost per mile vs. cost per trip. But there's one thing which I sort of gut felt that he spells out: transit friendly cities are denser, so they're more walkable as well.

Let me spell that out. In a sprawling car-centric city, up to 100% of trips may be taken by car. Actual numbers are more like 90%. [Caveat: that's share of trips to work, not all trips.] But you'll never see a city that's 90% transit mode share. (Some cities listed do get up to 70% transit, but again, that's commuting to work.) A city that has lots of transit is a city with lots of walking, too, especially if uses are decently mixed.

(I'm sort of imagining a degenerate case where there's no point to walking around one's residential neighborhood, not even for groceries or school or church, and having to catch transit elsewhere...)

So the reasonable target is not getting transit share really high, but car share low, with the slack being taken up by a mix of transit, walking, and bikes.

This has an extra economic effect: in Sprawlville, the cost of cars (roads, parking, cars, gas...) can be spread over almost all trips. Naively, the cost per trip of transit is doing to have a smaller denominator, only 40% of trips rather than 100%, even though the other non-car trips are part of a coherent dense system that must include transit.

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Damien Sullivan

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