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Monday, May 30, 2011

Transit and Journey to Work (JTW)

There is a famous census table called the 'journey to work', which asks "What mode of travel did you take to work'?, and lists alternatives such as 'private automobile', 'motorcycle', 'carpooled', 'worked from home', and a couple of different forms of transit.

The actual percent of people who take transit to work is pretty low. As the figure from shows, the vast majority of American's drive to work alone. Anti-transit propagandists like to harp that this number is little changed, despite significant investments in transit over the last decade.  Portland is a favorite target, because it shows minimal mode-shift, despite enormous record transit construction.

 But I was reading the latest Brookings report, and this phrase struck me:
The typical metropolitan resident can reach about 30 percent of jobs in their metropolitan area via transit in 90 minutes. 
Using Mode share to estimate transit usage is using the wrong divisor--it's like being told someone 'drove' from Florida to Puerto Rico--impossible. (Let us assume, for the sake of argument, that 1.5 hours is a reasonable amount of time to spend traveling to work--it's not). If only 30% of the jobs can be reached by transit, then the effective transit mode share needs to be revised. Multiple that by the mode share, you get a bit over 16%. If we lower the travel time to something saner (an hour), I'll bet the multiple rises, and so does the actual share of work-trips being made by transit, until it start looking a lot more like Melbourne, Australia:

Looking at the whole metro area, the car is clearly dominant. Looking at the CBD (a transit-rich area) and things look very different.