Ian Bicking: the old part of his blog

Transit and energy intensity

After an article on The Oil Drum I started looking up the energy intensity of different modes of transit. "Energy intensity" is the amount of energy required to do useful work (for instance, to move a passenger).

Here's what I found (from here; chapter 2, Tables 2.11 and 2.12):

                Btu/passenger-mile
Auto (highway)  3549   1.00 (relative to car; smaller is better)
Bus transit     4160   1.17
Bus intercity    932   0.26
Air             3587   1.01
Amtrak          2935   0.83
Rail transit    3228   0.91
Commuter rail   2751   0.78

Public transit also doesn't come off very well from this comparison. Admittedly highway automobile traffic is more efficient than city automobile traffic. But still the energy intensity of public transit is surprisingly bad. This is contrary to most people's intuition; I think this is why people expect public transit to be energy efficient:

One argument for rail or other mass transit is that it uses electrical power. Of course this is not a great environmental benefit now (at the moment it probably compounds the inefficiencies), but in the future it allows for the substitution of more environmentally friendly power generation. It's also strategically advantageous even if we continue to use fossil fuels, because unlike gasoline or diesel there are copious domestic fuels that can be used for generating electricity (like coal).

Then we should also ask: why is public transit so energy inefficient? Yes, it's better than cars, but only barely better. The answer of course is ridership -- if all the trains and buses were full all the time they'd be quite efficient. But they aren't full.

A naive response is that if we just need to encourage more public transit riders: by growing the systems, providing greater operating subsidies, and by taxing or tolling auto traffic. Once ridership is higher the efficiency will go up.

Does that really make sense? Consider some situations:

Commuter traffic:
At rush hour large numbers of people travel, often in particular directions. Vehicles have to bring people from their homes to work centers, then return the mostly-empty vehicles to make another trip.
Non-circular lines:
When you have a line that goes from one point to another point, typically somewhere in the center your line reaches its maximum utility and maximum ridership -- you've already passed many population sources, and are yet to reach many desired destinations. You need to have sufficient capacity to hold all those riders. At the start of the line you've passed only one population source (the terminal point); at the end of the line you have only one destination (the other terminal point). You will necessarily have less ridership (and empty seats) when you are close to one of the ends.
Off-peak service:
Let's say you want to provide comprehensive service (more about why you might want to do this later). Then you have to provide late-night service, and some service to low-density areas. These always have low ridership unless you are in an extremely dense area. Why is ridership always low? Well, if you've achieved good ridership from 6pm-8pm the transit system has to take on the burden of providing reasonable service from 8-10pm (after all, someone riding at 8pm very likely needs a return trip at 10pm). And if you get good 8-10pm ridership, you need to provide reasonable service from 10pm-midnight, and so on. "Reasonable" is a balance between geographic coverage and frequency, and the more "reasonable" the higher your potential ridership.

Why does off-peak service matter? Consider cost: public transit can be quite expensive -- $1.25-$2.00 a trip. Public transit proponents counter that cars are also expensive, but the costs are hidden. This is true, but the incremental cost of a car trip is fairly low. You've already bought the car, have the insurance, and the price of gas is not so high (even now). It's very hard for public transit to compete with the incremental cost of a car trip, except when tolls are very high (as in London) or parking is expensive. Even with parking it can be hard for public transit to compete when there are multiple passengers.

Public transit can only compete with the total cost of a car when it is a real option to actually ditch the car and rely solely on public transit (and perhaps other complementary services like taxis and car shares). If public transit doesn't provide reasonably comprehensive service it can't compete as a primary form of transportation. The complementary services help here, but they can be costly and might not be sufficiently flexible; relying too heavily on those will also cut into public transit's price advantage.

So what's my point? Mostly I feel that these problems need to be considered more honestly by public transportation advocates. But also we are at a point in history where transportation may change substantially; concerns about both peak oil and global warming mean we have to reconsider our current transportation infrastructure. Even without these concerns traffic itself is starting to become a major issue throughout the country, and there are no good near-term solutions; we're seeing substantially diminished returns when building new/larger roads.

What direction will we take going forward? Some are calling for an "Apollo Program" for alternative fuels; a huge, rapid, forceful program to fix our energy problems. Usually what this means is an attempt to switch cars from gas to something else -- usually biofuels, hydrogen or electricity. Traffic may be resolved through automated car lanes. Both kinds of technology are some ways off, but neither seems impossible.

Public transit proponents (and despite my negative tone here, I am one) usually have additional reasons they want public transit. There's a lot of good reasons (though not everyone will agree with all of them):

And more reasons I can't think of now, I'm sure. I want public transit to win over private transit. I just don't think the public transit we have is a very good contender. Maybe we can jam public transit initiatives through the government process once, or twice, or a few times -- but people have already noticed that these initiatives are incredibly expensive and underperform. Retorts that we just haven't tried it on a big enough scale aren't very convincing. Solutions like having the U.S. become Europe or Japan just aren't realistic; the U.S. just isn't any of those places, and just because something works there doesn't mean we can make it work here.

Mass transit today looks a lot like mass transit 75 or 100 years ago. People who believe in the promise of public transit need to demand something more. We need to stop apologizing for poor performing systems. We need to stop pretending it's reasonable to pay $2 to go five blocks, or that a 15mph system is fast enough, or that having to stand during your trip is a great way to meet new people.

What should we do in particular? In my opinion PRT holds more promise than any other system I've seen. Some people disagree, and they should offer up their own plans. But please don't try to just offer the same broken ideas as though they'll work this time. Existing systems (even ones that say they are new) simply aren't good enough.

Created 19 Nov '06

Comments:

So city auto "energy intensity" isn't included in that list. A quick survey of the net says that cars are about 30% less efficient when in city traffic. So, that table is now:

Auto (highway) 3549 1.00 (relative to car; smaller is better)
Auto (city) 4613 1.3 (car in city traffic)
Bus transit 4160 1.17
Bus intercity 932 0.26
Air 3587 1.01
Amtrak 2935 0.83
Rail transit 3228 0.91
Commuter rail 2751 0.78

All those non-car options are looking a little better now. I can see why the report would omit them, give it's angle. Yes, PRT systems look good, but will take a long time to replace the significant existing rail infrastructures we already have. We should still be encouraging people to take public transport over driving their own car.

# Richard Jones

Thanks for looking up the city energy intensity. Of course, it also assumes that cars have the same number of average passengers -- but honestly I have no idea if it would go up or down for city driving.

I can see why the report would omit them, give it's angle.

I don't really think the report has an angle. I do think they have specific data sources, and very possibly none of them covered city driving. I imagine it's much easier to figure out how many cars drive on highways than on city roads, and the other necessary numbers that go with that.

PRT systems look good, but will take a long time to replace the significant existing rail infrastructures we already have.

Do they have lots of existing rail infrastructure in Australia? We don't have hardly any for passenger use here. We have freight rail lines, which is what Amtrak also uses outside of the East coast, and that sucks. Much of the rail we have isn't of very high quality, and so it's not particularly fast or reliable to run on.

But PRT doesn't really have to replace existing infrastructure. There's a tremendous amount of in-fill that has to happen, regardless of the system, so there's a lot of new infrastructure that has to be built. Really it's hard to compare the two systems at that point, as no one proposes train systems with coverage anything like PRT systems. Trains simply don't scale that way -- the interchanges are difficult, and changing trains is too slow to have anything like a dense grid. It doesn't work great for Buses, but at least their stations are so cheap (i.e., just a sign) that they can provide good coverage that way. Though both trains and buses have a scaling problem where the speed of the system is slowed down by the number of stops -- so the better your station/stop coverage, the worse your travel time. PRT scales in a completely different way.

Also note that PRT infrastructure is far cheaper than traditional rail because the loads are so much less. Also because there is redundancy in the system it can be deployed incrementally, and repaired or upgraded without total system shutdowns. Rail does not do so well in that case and so repairs become extremely complicated and expensive operations.

# Ian Bicking

One thing that would affect these figures is that US rail is far more energy intensive than the rest of the world. The US idea of a commuter train is often some huge heavy thing with its own specific locomotive, compared to the "bus-on-rails" idea in Europe for example, with an underbody engine. I think the USA could use a fraction of the energy running public transit, if they wanted. Even US buses are much heavier and bigger-engine than European for example. So this would affect these figures..........

# Nick D

If anyone had these kinds of numbers for other countries, that would be awesome.

The US idea of a commuter train is often some huge heavy thing with its own specific locomotive, compared to the "bus-on-rails" idea in Europe for example, with an underbody engine.

"Transit rail" has an underbody engine, and does worse than commuter rail (though probably for other reasons). I think US transit rail uses essentially the same vehicles as in Europe, but I don't really know.

Even US buses are much heavier and bigger-engine than European for example.

For some reason we are very reluctant to run small buses. I'm not sure why; I suspect just to make the fleet more homogeneous, and because like every other kind of transit the people making these decisions don't care about the energy use. People in the US are probably also more tolerant of the size of buses on the street, so there's no pressure to reduce the amount of space they take up.

# Ian Bicking

A big reason US trains are not is efficient is because the US is nuts about safety. Thus US trains are often twice as heavy as European trains in order to make them crash worthy. There are probably many more road-level railway crossings in the US than in Europe. Still, the US is way more strict, and I don't know how effective that really is at preventing accidents. Surely it must lengthen the stopping distance, which would be safer if it could be shorter.

# James

The best way to make our existing transit system work is to increase the density. If you can average to people per car, the efficiency goes up, congestion goes down which also helps efficiency go up. I like the PRT idea but it requires a HUGE investment in infrastructure.

We have plenty of capacity it's just not utilized well. In the morning, there's a wide river of traffic going by my house. I know that many of those people are going close to the same place that I want to go. If there was just some way to link us up, we could share the ride.

I'd like to see a dynamic carpool system. Use the GPS built into the cell phones along with the wireless network to allow people to log in their morning and evening routes. Other people needing a ride would log in their request. I computer would link up riders to available drivers and send directions to the driver to pick them up. I don't carpool now because my schedule is to random. I don't know exactly when I can leave in the evening. With a dynamic carpool, I wouldn't need to. When I'm ready, I just go down to the street and request a ride then wait for the pickup.

This system works best when there's a lot of traffic. Lots of cars increase your chance of finding someone going near to your location. It scales up when you need most capacity and avoids that round trip problem that you mentioned.

For off hours, you have a couple of thousand taxi like shuttles on non-determined routes picking up and dropping off people when they request a ride.

Look at the advantages; low or no infrastructure costs, door to door service, 24 hour service cheaper than the other methods. All you need is the software to track drivers and riders over the cell network and send the instructions to link them up. Granted, that software might be difficult to write but I don't think it's impossible.G

Getting people to participate would be the hardest part. You can use the existing carpool programs to encourage ridership. If the system caught on, you could possibly live in a western city without a car.

# Joe Goldthwaite

I like the PRT idea but it requires a HUGE investment in infrastructure.

While your car pooling idea requires less (additional) infrastructure, all rail-based transit has much higher infrastructure cost than PRT, and PRT should be cheaper than highway lanes of similar capacity. Of course PRT can't replace the flexibility of roads (which carry things like moving trucks, construction equipment, bikes, ambulances, etc), so it's not really right to compare it to basic road infrastructure (which is inevitably required); but it compares quite favorably to the cost of increasing road capacities. And as an immature technology there's more avenues open to improve it.

While responsive car pooling or taxi service doesn't require new infrastructure (instead increasing the capacity of current infrastructure) the energy intensity improvements seem limited. It would feature smaller vehicles, and by being more responsive and adaptive it could carry a higher number of average passengers. But it still requires vehicles larger than a typical car, and I imagine cars would frequently be running at less than full capacity. I wonder what the energy intensity of a normal taxi is? Probably atrocious -- they frequently drive around with no passengers at all, and tend to use fuel-inefficient vehicles. Ride share systems would certainly be a big improvement over that, and probably buses, but not a huge win. Though by using less vehicles more intensely you can afford to invest more heavily in fuel-saving vehicles or in vehicle upgrades. Anyway, an interesting idea.

# Ian Bicking

I guess the idea isn't new. Here's a paper from 1968;

http://faculty.washington.edu/jbs/itrans/tomtrans.htm

# Joe Goldthwaite

Ahh yes, but my Hybrid does much better in city traffic than on the highway 58-60 in town vs 48-52 on the highway.

I think transit is a loser for one reason seldom mentioned. No matter how good it is or how dense the neighborhood it is controlled by politics, and that is always inefficient. Also, no matter how good it is, aut travel always offers options and destinations thet transit cannot.

# Ray Hyde

No matter how good it is or how dense the neighborhood it is controlled by politics, and that is always inefficient.

This is true of all transit -- road construction is also very political. Anything that involves the public space is political.

# Ian Bicking

Ahh yes, but my Hybrid does much better in city traffic than on the highway 58-60 in town vs 48-52 on the highway.

I think transit is a loser for one reason seldom mentioned. No matter how good it is or how dense the neighborhood it is controlled by politics, and that is always inefficient. Also, no matter how good it is, aut travel always offers options and destinations thet transit cannot.

# Ray Hyde

Cars epitomities rabble individuality, while public transport are like governments. We could do with a system which solves the problem of car pooling, for instance, through social reputation, better interconnectedness and alternatives.

# Chui

Re suburban culture, I just wanted to point out this article on a recent study that found suburbanites have more friends and are more involved in community: http://www.canada.com/topics/news/national/story.html?id=78c72193-8f5e-4ae3-8b10-e9cc058a8047&k=14483

# Jonathan Ellis

There's certainly a lot of good things about the suburbs. Lots of the tolerance and diversity of the city are just built on the apathy and indifference of the populace towards each other.

Personally I don't think centralized cities are a good idea -- cities where there's a strong downtown that is the center of activity, and a blending to residential building from that. I'd prefer medium density with lots of room for diverse and eclectic land usage -- on all scales, down to mixed use blocks and buildings. This isn't anti-suburb really, though it is something that traditionally suburbs have outlawed through strict and highly separated zoning.

One of the things I like about PRT is that it's a transit system with no center. People can choose what their center is, and it will likely overlap with other views of the community -- since really there's always a set of overlapping communities, not segmented communities. This can respond much better to self-directed changes in communities over time, and without any overarching plans.

# Ian Bicking

thank you, it is about time a proponant of public transit acknolwledged the problems it has.

# Hank Miller

What about the bicycle?

# Joseph Huang

I have a proposal that you may not have seen...

http://www.pptproject.com

This is similar to the PRT concepts that have been proposed, except that it REPLACES the automobile. Feedback is welcome...

gary

# gary

PRT is only a concept. LRT is a proven success. Here's a video that dispells the myths that PRTistas spin about LRT being "old-fashioned' and ineficient:

http://www.youtube.com/watch?v=e_huq8g8JiQ

Videos about PRT here:

http://dumpmarkolson.blogspot.com

# Avidor

Avidor,

> PRT is only a concept.

Absolutely correct.

> LRT is a proven success.

That really depends on how you define success. We have one in our town, but only a very tiny fraction of the population are in a position to utilize it. It appears empty most of the time. So if you define success as an alternative to the automobile, I would say it fails. The numbers just aren't there.

As for the dumpmarkolson blog, I don't know who Mark Olson is. I've know of J. Edward Anderson, but only vaguely. I have no connection to either one so I'm at a loss to understand you point.

gary

http://www.pptproject.com

# gary

I had the PRT fantasy even before I knew what it was called. It's main problem is the chicken-and-egg 'needs to have world domination before it's successful' issue. It can't build up the way something like EZ-pass did, which needed MUCH less infrastructure. My favorite theory on how mass-transit will evolve is basically that self-navigating/crash-avoiding technologies will evolve and mature at the same time as Japan-like minicar options will become more available near American cities (e.g. Vespas with 4 wheels). Self-navigation will eventually become good enough to navigate huge traffic flows (From a tech perspective, if 802.11s can do it at gigabyte speeds, it can definitely be done at >1millisecond speeds for cars) and most cars by then will be powered by electricity. Then hopefully, all it will take is a couple cities to pay for specialized car/rail connections for continuous power. Then the connections may become available to the population (maybe!).
# Schuyler