Wednesday, January 16, 2008

Bus vs. Rail vs. PRT

It's a shame, but advocates of public transit are divided over modes of transit, and sometimes get into ugly fights about it.

There's not much of a fight between bus and light rail - not that I've seen, anyway. Bus is less expensive, less rigid, and less popular. The user experience on a bus is bumpier and jerkier than on rail. Want to use your laptop? Even when there's space to open it up, the ride is too rough. Riding the Orange Line BRT (Bus Rapid Transit) in North Hollywood CA (October 2007) was just a bit smoother than regular line buses because there were fewer stops and the roadway was relatively new and smooth, but I still wouldn't have wanted to use my laptop. It was far too crowded anyway.

In many areas, bus riding is associated with poverty. That's a shame. Cities like Seattle, where until very recently there was no light rail, have buses filled with strap-hanging entrepreneurs and technocrats. Around here, polite folks don't talk about that association, but it's the elephant in the living room. The stigma can only be overcome by time, I suppose.

Light rail is hands-down more expensive than bus lines. No question. For reasons unfathomable to me, the poverty stigma isn't there. It's a bit smoother if the track is conscientiously maintained, but that's not the main advantage. The big advantage is the value it adds to real estate within a few minutes walk of the stops. Studies have shown that for every dollar invested in rail rapid transit, the local economy recovers between $4 and $8. At TRU (Transit Riders United, Detroit) we like to use the figure $6. Why does rail return that kind of money when buses don't? The common sense answer is simple: the route is going to stay in one place.

In other words, lack of flexibility is its big financial advantage.

But the ugly fighting among the transit brethren is between those espousing light rail and those dreaming of PRT (Personal Rapid Transit). I am not sure why the fight is so ugly, because what I've seen of it descends to ad hominem arguments. "You're just in it for the money!" from the PRT people, while light rail folks answer, "Well, you're an ignorant, starry-eyed dreamer!"

Of course there are the non-transit people who get nasty toward anyone who wants to take money away from highways. One particularly vitriolic YouTube piece blames Minneapolis City Council members who want to investigate PRT, for the collapse of the I-35 bridge in July, 2007. Nicely done piece of nonsense, not worth refuting for the benefit of intelligent people.

PRT vs. light rail is worth thinking about a little more. PRT is a great idea that's under development, but untried. It's been described as a "personal monorail" system, or an "automatic taxi". Instead of vehicles holding 40-80 passengers, each vehicle holds 5-6. Instead of a human driver, it's an automated, grade-separated system. Passengers enter their destination, and the vehicle takes them there. You don't have to share a vehicle with anyone if you don't want to.

The main advantages of PRT are its convenience and its appeal as something new. The main disadvantages are that it has never been put into actual day-to-day use (though there are experimental systems) and that it is not intended to carry large numbers of people. PRT advocates like to say, "You never have to wait for a vehicle." Of course that's true until the system reaches saturation. Without everyday use, there are too many unknowns to predict accurately when the saturation point will be reached. Advocates also say that PRT systems are less expensive to build than light rail. I've never seen any hard facts to justify that claim. I sincerely hope it proves true.

Light rail is very much a known quantity. The technology has been perfected over almost 120 years' time. We know its strengths - and its weaknesses. The costs are fairly predictable. They can move a pretty good number of people - less than heavy rail, of course, but more than bus or what PRT claims I've seen.

I really don't want to throw you the cliché that PRT is "they way of the future". What the heck - I just did anyway. But I'd really like to see PRT tried in the USA. It will probably be tried first in Europe or Korea, and that won't carry much weight with Americans because "We're different from them". So we have to do it ourselves. *Sigh* I suppose it's manifest destiny all over again.

Interested in PRT? Here's a link to my "best of PRT" links:
Wikipedia has a nice article with lots of links, too:

1 comment:

  1. PRT advocates like to say, "You never have to wait for a vehicle." Of course that's true until the system reaches saturation.

    PRT isn't designed for high passenger density. But there are PRT-like systems with higher passenger density (more passengers per vehicle); some are called "group rapid transit" or "ultra-light rail". At any rate, passenger density of PRT can't be any worse than passenger density of a lane of highway, so it's at least a marginal improvement over personal automobiles as far as throughput is concerned.

    A useful way to think of PRT is as a driverless taxi system but using a track or guideway for guidance rather than a machine vision algorithm. The plus is that it's much safer, allows for higher speeds, and we already have the technology. The minus is that it's likely a lot more expensive, at least for the initial capital investment--though buying an additional podcar is likely a lot cheaper than buying an additional driverless automobile.

    I think the animosity you've witnessed between LRT and PRT supporters is among only a handful of boisterous individuals in each camp. Most of it consists of FUD and is completely uproductive. There are plenty of quantitative and qualitative measures that can be used to compare the pros and cons of each technology but they simply ignore them and waste everybody's time.

    PRT is a promising concept but still faces some hurdles, both technological and psychological, before it can see the full light of day. LRT is tried and true but does have some shortcomings that make it less attractive to potential riders than some of us would like.

    I actually think what will break the stalemate is gradually incorporating ideas from PRT in conventional transit systems. Grade separation, offline stations, and more express service can provide much, though not all, of the benefit that PRT promises without abandoning existing transit paradigms.