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I’ve been reading a book on transit and traffic in the 20th century, devouring its dates, facts, and tables, when I was brought up short by a familiar phrase.  “Per-capita”.  A terrible, but easy phrase to use with transportation.

A better metric would of course be per mile, as some people don’t even use transportation, and others are limited through ge or infirmity in their use.  A metric like person miles traveled per mile of way, or trips per mile of way, would be more relevant.  I understand this is harder data to get, and its still not as descriptive as it needs to be.

As I’ve mentioned before, nobody experiences life in the aggregate.  We experience it from our points of view.  I can say that Atlantans on the average have a worse commute than Columbians on the average.  I cannot infer that most Atlantans have a truly worse commute however, because I know nothing about the routes and needs of Columbians and Atlantans.  One person with a 5 hour commute counts as much as ten with a ten minute commute.  One road in Columbia could be regularly more hellishly congested than any road in Atlanta, but because only a few hundred drivers

The problem with comparing transit versus traffic usage per capita is that traffic goes everywhere, while transit only goes along transit routes.  The more people, jobs and hosing are along those transit routes, the mrs people will be able to use transit.  If transit doesn’t go where you need in a timely fashion, then you don’t use transit.  Fortunately, we had 4.5 million route miles and 800 million parking spaces built in the last century to let you use traffic to get everywhere with a street address.  And everywhere has a street address.

We don’t talk about a crisis in ferries because per capita ferry use is way down for commuters from the 17th century.  Ferries are essentially bound to bays and rivers.  Now that we have bridges, we use ferries a lot less.  But for thousands of commuters in metro Seattle, New York and Boston, the ferry is still an indispensable part of their commute.

Assuming $3 ml / traffic lane mile and $100 ml / transit route mile

As we can see from the above table,we have built many more roads than transit lines in our cities.  Roads don’t function very well unless they are connected to lots of other roads.  They also don’t function well under high volumes without multiple lanes.  The closer they get to capacity (at 40% of capacity, actually), the more traffic engineers start to plan to add more lanes in one or more directions.  The $3 million per mile of new traffic lane Is nothing like the $100 million per mile of transit, but nobody uses all the miles in their town.  People use far less of their road networks than they do their transit networks, even if they take the train once a year.