What's better than public transportation?

I'm a big fan of public transportation. The ability to survive without owning a car would lead to a tremendous reduction in cost-of-living. Reduction in traffic is in everyone's best interest. And not having to drive every day would let me get a lot more reading done. (Or more realistically, sleep.)

But here in Nashville, the bus system is more or less a joke for much of the city. I live in the city limits, and I could get to work by bus, but I'd have to spend ninety minutes instead of twenty, I'd get there late, and I'd spend more money. The many thousands in the exurbs are pretty much hosed except for the Music City Star, and even then your options once you reach Nashville are limited.

The more I think about it, the more I think the emphasis on trains and buses may be misplaced. Mass transit as a concept has one inherent limitation: each rider wants to stop at only two places, and no others. The more riders there are wanting different stops, the less convenient it gets for everyone involved. But the fewer stops the bus (or train or whatever) makes, the fewer people the bus is convenient for. You want a very high person-to-stop ratio. This only works for high-density end-to-end traffic paths, like an express from a park-and-ride, a commuter train, or a small local circuit in a high-density area.

But what about those of us (and I'd guess we're the majority) who neither live nor work in high-density areas? By definition, we collectively have more stops to make. To keep a high person-to-stop ratio, you have to reduce the number of people per vehicle. Perhaps to, say, five.

I argue that mass carpooling could have more effect getting cars off the road than any imaginable public transportation system. Say we're comparing three options: 60-person buses, 5-person carpools, and the default single-occupant car. If there are six thousand people commuting from Clarksville (to pick a random number and exurb), that's six thousand cars, twelve hundred carpools, or one hundred buses. Obviously both carpools and buses are vast improvements to traffic. And if everyone would ride the busses, they win over carpools. But not everyone will bus, because of the lack of flexibility.

So the next question is, how many people are willing to bus? How many are willing to carpool? And at what point does realistic carpooling get more vehicles off the road than busing? I won't bore you with my algebraic prowess (maybe later), but in our case the answer works out to be pretty interesting: regardless of the number of people involved, if just 25% more people are willing to carpool than are willing to bus, mass carpooling gets more vehicles off the road. This even though a bus holds twelve times more people! Since a carpool is far more convenient than a bus, I'd expect far more than 25% greater ridership.

Now let's consider cost. If you've got 100 busses, that's at least $30,000,000 in capital expenditure. Probably more. Each bus costs around $100/hr to run. Even if you assume they only run four hours a day (two round trips), that's $40,000/day, or $10,000,000 a year in operating costs. Assuming each bus lasts ten years, that's $13,000,000/year to get 5,900 vehicles off the road. This seems like a lot, but consider that adding a lane of interstate between Nashville and Clarksville would cost something like $150,000,000 and take several years.

How about gasoline? A hundred mile round trip at 25 mpg costs $15 a day. That's $22 million a year in gasoline saved by getting those 5900 cars off the road! That's a number so big I almost want to cry.

Further, consider that traffic can add half an hour to your commute each way. One hour a day saved, times six thousand drivers, is 1.5 million man-hours per year. Figure an average wage of $12/hr, and $13,000,000/year starts to sound cheap.  If we come up with a solution that makes a significant reduction in traffic that only costs, say, a million dollars a year, we collectively are coming out way ahead.

So here's the idea: we should pay people to carpool. But not at a flat rate. Put a million dollars in a pot, and declare that that pot will be distributed evenly among everyone who carpools that year, weighted by how many days they do it. Imagine how people would respond to an incentive like that! If only five people carpool all year, boom, easy $200k each. Pay it out more often than once a year, too. Say every two weeks. Within a few months you should reach an equilibrium point where exactly the right number of people are carpooling for the money being offered. After that you can see just how good the system is and how much it's worth.

As an added bonus, you could let people without cars sign up for the system, and basically turn every driver in the city into a government-provided taxi for the carless. The driver gets paid by the number of passengers, so its a win for them. And the car-free individual gets better service than busses.

The problem is making the matches. If you could get our hypothetical six thousand people to put their schedules in a system, a relatively simple computer program could make matches between them and make a huge dent in traffic. There are already such systems, but there's relatively little data in them. Paying people to participate will fix that. And with smart phones becoming ubiquitous, hitching a ride without advance planning becomes easy.

Now, how does this apply to the Amp? To be clear, I’m not presently taking sides in the debate over the Amp. Traffic on West End is abysmal, and something needs to be done. The Amp is, indeed, something. But what alternatives are there? I think this alternative is better from almost every perspective. Let's run the numbers.

Amp is projected to cost $4 million a year to operate, plus the $174 million startup costs. Add some for inevitable overruns, divide that over 20 years, and you get about $14 million annually. A comparable BRT system in Cleveland has ridership of around 14,000 daily. Each rider represents at most one car off the road, but maybe not even that. Depends on whether they count the same person going both directions as one rider or two. So being generous, we’re spending at least a thousand dollars per year to get each individual car off the road.

How about instead, we just pay people to carpool? If someone paid me a thousand dollars a year for my trouble, you can bet I’d be carpooling! Set up a good smartphone-based system to make ride matches, and I guarantee you you’ll get more cars off the road for less money. The result helps all of Nashville, not just one dense strip. And there’s zero construction disruption.

Obviously there’s a lot of variation possible. Who gets paid? The driver? The rider? Both? How do you keep track and minimize gaming the system? I don’t have all the answers. I can tell you that the system has to be set up well from the start; I've seen far too many systems like this half-complete with clearly zero ease-of-use consideration. The problem isn't trivial. But it is solvable, and I think this is what we should be looking at as an alternative to ripping up West End for a few years.

Footnote:

Suppose you have two forms of transit available to people. Cars, which hold 5 people, and busses, which hold 60. Suppose your goal is to get as many vehicles off the road as possible. For cars to get more people off the road than busses, more people have to be willing to use cars than are willing to use busses. How many more?

Define DB to be the number of people held by a bus, and DC to be the number of people held by a car. The ratio of people willing to carpool vs. number willing to bus must be at least (1-1/DB)/(1-1/DC)

If this criterion is met, more vehicles will be off the road by carpooling, even though each vehicle holds fewer people.