How should we measure SMART's effectiveness?

On August 4, Wayne County voters decide on a millage that would let Metro Detroit's suburban bus system, SMART, significantly expand service. Local anti-transit activist Matthew Wilk calls this potential funding increase a "waste," and he's always using one statistic to prove his case: SMART buses, he says, average just 3.9 riders .

"Our best advertisement against this tax is buses driving around town — because they drive around empty,” Wilk said.

It's the sort of effective anti-transit messaging that has worked for decades in Metro Detroit, because it conjures the image of a 60-seat bus going down the road with only 4 people on it that appeals to many people's preexisting biases about transit.

Let's talk about where this number comes from, and, more importantly why it says nothing about whether SMART is worth funding.

Where 3.9 actually comes from

The federal National Transit Database publishes yearly profiles of every transit agency in the country, including SMART. These profiles contain a number of statistics, but you won't find the "3.9" figure Wilk references directly on the page. He builds it himself with the following numbers:

SMART vehicles across all modes traveled about 12.5 million "revenue miles" last year (i.e. it was actively providing transit service)

SMART passengers across all modes traveled just under 49 million miles in total

48,784,608 annual passenger miles divided by 12,554,344 annual vehicle revenue miles = ~3.9

This statistic is average occupancy. A suburban bus system that's oriented toward providing coverage across a large area, such as SMART, will have a low average occupancy because of what that service area looks like. But that doesn't mean that it's not doing its job or that it's not providing benefits to society.

A problem with using mileage-derived statistics to try and make your case with an "average riders per bus" (or, really, any transportation metric) is that you introduce a bias in relation to physically longer trips. Imagine two riders of the SMART bus system:

Alice takes a 4-mile round-trip commute and runs a 2-mile errand every day.

Bob takes a daily round-trip commute of 12 miles.

By passenger-miles, Bob (24 miles/day) "counts" twice as much as Alice (12 miles/day), even though Alice rides more often and derives more usefulness from the system. There's no perfect way to measure the effectiveness of a transit system, but Wilk is cherrypicking numbers here to make his case in a disingenuous way.

Note: One basic problem with Wilk's use of this specific calculation is that these figures include SMART's "Flex" micro-transit service (which runs at less than 1 person per vehicle by design) mileage alongside regular, fixed route buses that everyone thinks of when you use the term "bus". Removing the Flex mileage causes the average occupancy for fixed-route buses to go up to 4.8.

Average occupancy mainly measures density

Let's do a bit of comparison with other bus systems in the US. How do other transit agencies score with this metric?

New York City | 1.19B / 83.1M, for 14.4

San Francisco : 168M / 13.3M, for 12.6

Chicago : 449M / 49.5M, for 9.1

Detroit/ DDOT : 70.1M / 9.13M , for 7.6

Cleveland : 73.3M / 13.4M, for 5.5

SMART: 4.8

Ann Arbor : 15.9M / 3.55M, for 4.5

If the busiest bus systems in the country, in the most transit-friendly conditions imaginable, can only get to two or three times SMART's average occupancy number, SMART's 4.8 isn't the huge problem Wilk's argument needs it to be. Average occupancy is mainly a function of land use and density (which are completely out of SMART's control), not transit agency effectiveness.

For reasons that are both political and physical, SMART is obligated to run transit service in areas that don't naturally support it , where houses and businesses are simply physically farther from each other. These routes generate a low passengers-per-revenue-mile relative to routes like the FAST Gratiot/Michigan/Woodward routes, which spend most of their time (and generate most of their ridership) in dense urban corridors.

Wilk claims that he's not just reflexively anti-transit:

“That’s not to say that public transportation is not necessary. We feel that it just has to be done right.”

If he is truly interested in this question, he should say what "public transportation... done right" looks like, particular in areas like western Wayne County. He's wrong to point at the average occupancy figure as a sole judge of the value SMART provides to the region, and his use of this statistic makes me doubt his professed interest in better transit. I also hope that going forward, the media covering this fight can start to more critically look at the basis of most anti-transit arguments.