Some further half-baked thoughts on fares and metrics.  My goal in writing this is not to break new ground, but rather to summarize many of the common-sense ideas I’ve heard others say.  I’m sure others who have studied transit have come up with better summaries.

The overarching metric I’m kicking around is mobility per subsidy.   This pushes the hard work back one level into defining mobility and subsidy, but I think mobility is a useful idea inside of which one can compare submetrics.

First, the denominator: Subsidy here means the total revenue the transit agency receives from taxes.  Why per subsidy and not per dollar?  Because, from this perspective, we are judging the transit agency based on how effective it is in working with tax dollars.  If a transit agency sells advertising and uses that revenue to improve the service, the marginal improvements it funds will probably not be as cost-effective as the first dollars spent, but it would be perverse to judge the transit agency as having provided worse mobility to the taxpayer because they found new revenue sources and put the money to use!

How does subsidy interplay with costs?  For the purpose of this analysis, I’m assuming that the transit agency cannot run a significant surplus or deficit over time, and therefore costs are equal to revenues.

What is mobility?  Roughly, getting people where they want and need to go.  I choose this concept because it nicely encompasses some of the other concepts that people have bandied about for transit metrics.

For example, what’s the difference between ridership and mobility?  If ridership is measured as number of rides in a system, this is an imperfect measurement of mobility.  A system that connects linear points A, B, and C might have two buses that connect A to B and B to C .  Through-running a single bus from A to B to C will reduce the number of rides needed to get from A to C from 2 to 1, but increase mobility by making it possible to take one bus from A to C.   In this sense, number of trips is closer to mobility than number of rides, and fits our commonsense notion of what a better system should be.

But number of trips is an imperfect metric as well, as some trips aid mobility more than others.  Setting the fare of UT shuttle buses like the FA to zero has helped them become some of the highest-ridership buses in the entire Capital Metro system.  Many of these trips are vitally necessary: say, students going to class.  Some of them, though, aid mobility negligibly: say, students hopping the bus for a single block they could’ve walked because it was there and it was free.

However, distance traveled itself isn’t a good metric of mobility.  The student who takes a bus 2 miles to go to class could not feasibly walk to class every day any more so than the student who takes a bus 12 miles.  A bus trip of 2 miles therefore is providing as much mobility as a bus trip of 12 miles.

Mobility already encompasses some common sense notions of equity.  Some people are in greater need of transit services: people for whom it’s harder to substitute other transportation.  For example, people with mobility impairments preventing them from walking or driving, or people too poor to own a car.  However, there are notions of equity that are incompatible with mobility.  For example, some of those who need the most help and who use the transit system may be those who use buses as a cheap air-conditioned environment.  However, while these may be people in need, the transit system should not prioritize their needs, as the transit system is meant for providing transit, not any social service that is needed.  That allows city and county governments to compare spending additional funds on air conditioning for the needy to other priorities.

Finally, one note: mobility per subsidy is mainly a useful metric at the margin.  Spending more money overall on transit might reduce the overall efficiency of the spending, as the last bus unit added will probably add less mobility than the first.  However, it can be useful in determining which of many routes should be added or whether it’s worthwhile to raise fares and use the money raised to provide additional service.