Brad Ideas - Is Green U.S. Transit a whopping myth? - Comments

The "real" answer

brad — Sat, 23 Apr 2011 13:37:08 -0700

While it is true that reducing travel, or not building sprawl would reduce energy use. But when you talk about the “real” answer the big question is, can you get people to do it? The extent to which people will be greener for the sake of being green is not zero but it is fairly limited, especially if it costs them time, convenience or money or other things they truly value, particularly having safe environments with places for their kids to play.

The real answer has to be both greener, and desired by the public. You can pass laws but even the power of that is limited.

The real green is LESS MILES

AaronW — Fri, 22 Apr 2011 14:37:39 -0700

So air travel looks not so bad by this chart... well, that's because per-passenger it isn't so much worse than driving the whole way. But it's the distance that is the real problem. The problem with private cars isn't the inherent efficiency, it's the idea that private cars let people live in spread out sprawl and drive everywhere. If people live near transit, then they go less total miles and use less land in sprawling McMansions. It's definitely less efficient to have a bus or train go through winding subdivisions versus cars! The real answer is not to build these ridiculous subdivisions. But anyway, there are also issues of infrastructure and quality of life, because a traffic jam is a lot worse than sitting in a crowded moving train, and roads need more repair over years than rail, not to mention have more dangerous accidents and cause more stress...

Amtrak

brad — Fri, 18 Feb 2011 14:39:45 -0800

Is 2398 btus/passenger-mile in the 2008 DoE data book. There are links to the data book in the article above. That’s about 50 passenger-miles/gallon of gasoline — they use higher energy diesel so it will be a bit higher than that per gallon of diesel.

HSR figures though could vary greatly from this.

HSR will probably be electric. Electric efficiency varies greatly from grid to grid, but it tends to be somewhat higher than diesel.
It really all depends on load factor. Amtrak has pretty good load factor, I have to presume, because it does not run frequently and does not have to run frequently (unlike transit.)
High speed trains are less efficient than slower trains due to high aerodynamic drag, but tend to have better aerodynamic shapes, and may be longer to make up for it. Energy lost do drag goes up with the square of velocity, so a 180 mph train has 9 times the energy need per mile over the same train at 60mph. Aircraft make up for this by flying high where air is thin.

Can you please post Amtrak numbers?

Jason — Fri, 18 Feb 2011 13:30:11 -0800

Hi Brad, I recently rediscovered this site after a related discussion on high-speed rail at work. This site is simply the best analysis of mass transit efficiency I've ever seen. You noted in a comment that you don't list Amtrak because it is not considered a form of transit, but I think it would be very useful to show these numbers considering current debates around high-speed rail in the US. Would you mind adding Amtrak to your post charts or (at least) including the BTU per passenger mile number in a reply to my comment? Thanks!

Btw, the 2011 Insight EPA combined MPG appears to be 40/43 and Consumer Reports (CR) got 29/45 in real road tests (38 combined). Am I correct in thinking that the Prius is currently the best transit competitor in the US? CR reported 32/55 in real road tests (44 combined), EPA says 51/48. My experience is that CR numbers are more accurate.

Pretty close

brad — Tue, 12 Oct 2010 23:52:25 -0700

And in any city that didn’t have a very limited number of streets going to the CBD you would not need to use this temporary switch to real buses.

It’s just a square footage thing. A person in a robocar needs about 50 square feet plus their headway space (whatever that is) while a bus with 50 people needs 400 square feet plus the bus headway space.

How much headway? People debate that. Ordinary cars try for about 1.8 seconds at highway speed. Robocars can of course do better and eventually can draft. However, my own safety algorithms call for never occupying more than 50% of the road space, so that there is always room for vehicles to swerve into gaps if the need comes.

Virtual Bus

Stuart Lynne — Tue, 12 Oct 2010 20:23:00 -0700

Wouldn't the various RoboCars simply assemble into a Virtual Bus? I.e. minimal spacing, lead vehicle controls speed and direction, following vehicles just react to speed changes in the vehicle ahead. Higher density and better fuel efficiency from drafting. Not quite as dense perhaps but more efficient for latency (i.e. users time) as long as the overall capacity of the road network is adequate.

Bike Safety and Cars

Stuart Lynne — Tue, 12 Oct 2010 20:16:26 -0700

Bike safety is highly incumbent on not getting hit by larger vehicles, as in cars, trucks, busses, etc.

I spend many hours a year on a bike and look forward to a RoboCar world. First they'll weight less so if you get hit by one it will hurt less. Second they will be much better at avoiding me. And finally won't intentionally buzz, honk or hit the brakes after swerving in front of me.

Road capacity

brad — Tue, 12 Oct 2010 00:50:59 -0700

Road capacity is actually quite large. I am working up some articles on that. It would not take 167 inbound lanes with robocars. That’s a number for today’s cars.

Imagine the cars were just 4’ wide and 10’ long, and ran on a 1 second headway instead of the 2 second headway we try with regular cars. That would be 54 regular sized lanes, which still seems like a lot, but in fact if you don’t have cars parked on the side of the road a typical “2 lane” street actually has 4 lanes, so it’s just 27 ordinary streets if you can redirect at rush hour, and clear away at rush hour. And just 18 of the “2 lanes each way plus one lane for parking” minor arterials, which most cities do have going in, though Manhattan is of course unusual as an island with a limited number of bridges and tunnels.

However, consider what you could do in phase 2, which is robotic buses. Imagine that people’s incoming robotic cars gather in parking lots on paths to the bridge, and 50 people get out and get quickly into a robotic bus. The bus takes them over the bridge to another lot, where 50 single person robocars await. They quickly get into those and are taken along Manhattan’s wide avenues and streets to their destinations, and then the cars come back for more.

Now let’s put the buses back to regular car headway or 2,000 vehicles per hour. Here just the 3 lanes of the Brooklyn bridge (in one direction) are enough to bring 300,000 people per hour into Manhattan — again on just the Brooklyn Bridge. Add the Manhattan bridge and you have enough for almost 700,000 people per hour. Buses are transit you might say, but these are unlike transit as you know it. You would only ride them for a few minutes to get around the bridge bottleneck, and there would be no waiting either to get the bus or for your robocar when you got off it. (You might wait for a slot on a bus, but you would wait at home, your own robocar not leaving until it is scheduled to meet a bus on which you have a reserved slot, and the other 49 people’s cars doing the same.)

Now this is extreme. We would not do it this way for many reasons. First of all there are lots of bridges and tunnels and lots of capacity, especially with reversed lanes. And we do still have those subways so we would keep using them, though we would use them in concert with robocars (which might get entrances to drive down to the platform level) and they would make far fewer stops to be express. Because the buses would be simply cycling back and forth over the bridge, you would not need an endless supply. With a 15 minute round trip, 3 lanes of buses would require 1,500 buses, which seems like a lot but there are probably that many subway cars. If the buses were standup rather than sit-down they could hold even more, and could do even better if they were articulated multi-car buses, which would not be a problem for a gig like this.

No, the robocar capacity, in its full form in the all-robocar world, is immense, and dwarfs any transit system. How could it not, when there are so many miles of road, and transit rails are no different from road in capacity once you can fully control them. That’s some time away, but so is the withering of transit.

Once you get to a certain density, cars can't work.

Sam — Mon, 11 Oct 2010 21:21:58 -0700

As far as public transport vs cars, there are cases where cars could not possibly provide the service, regardless of energy efficiency. For instance, on average in 2007 the NYC subway system transported 388,802 people into the business district of Manhattan between 8am and 9am. To get the same with cars would take at least 167 inbound lanes of bridges and tunnels.

http://frumin.net/ation/2009/08/whats_capacity_go_to_do_with_m.html

Chaffeurs

brad — Thu, 12 Aug 2010 10:41:44 -0700

Yes, I suspect this error is present in the DoE’s numbers. However, I am curious if you have information as to what the magnitude of the difference would be, ie. what fraction of total road travel is “support” like cabs. In Manhattan the value would be quite large but in most other cities I don’t see the cab volume as super high, and it’s quite minimal on the highways and suburban roads.

One can debate if transporting the kids counts, since the parent is not just driving, but supervising the children. Now I personally agree with those who say we over-do this and young kids should be able to ride transit from school (in the cases where it exists) and I certainly rode it when I was 9, but most parents are not this way.

However, that’s beside the point because my guess is this does not tweak the numbers a great deal. You say it’s a fundamental flaw so I presume you have numbers to show it’s much, much larger? I do expect (or hope) that people will be more willing to trust children to a robocar, with a constant videoconference link back to a trusted supervisory adult for the ride. But that’s for the future.

Flawed Fundamental Assumption

David — Thu, 12 Aug 2010 06:03:46 -0700

Your numbers assume that all occupants in a car are passengers. If the driver is operating the car to "pick up the kids at school" or "drop off the spouse at the airport," then they themselves are not a passenger, and the car has exactly zero passengers for half the trip.

You're including potentially empty subways while assuming taxicabs are never without a fare.

How do the numbers compare if the driver is only truly a passenger, say, 80% of the time?

It's complex

brad — Wed, 14 Jul 2010 11:25:13 -0700

Energy loss comes from 3 things mainly — engine inefficiency, rolling resistance, and air drag. Long trains have low air drag per person (when fully). Steel on steel and maglev are very good for rolling resistance. Maglev is of course super good.

HIGH SPEED RAIL

kieth nissen — Fri, 09 Jul 2010 17:00:14 -0700

I think the author or someone on the same wavelength (I almost wrote "wavelink") has commented that using smaller, lighter vehicles designed for much
slower speeds would improve energy efficiency a lot. That sounds reasonable to me. But I note that the very high speed Japanese "East" line rates excellent. Do the laws of physics (where I think resistance increases proportional to the square of the velocity, something like that) get bent with high speed non-levitating trains? obviously I can see that a long train presents a proportionally small area to atmospheric resistance but I would expect that friction to be a huge factor. Any comment?

This misses the point

brad — Sat, 03 Jul 2010 14:22:05 -0700

As I say, adding yourself to any vehicle (carpool or train or bus) that is already going is indeed the efficient choice, but these numbers are based on what happens in the real world, among people who by and large know that. Saying, “Transit would be more efficient if people would only ride it” imagines we have a magic wand that will make that happen. People take the path that is cheapest and most pleasant and convenient for them, and I don’t see much success in changing that.

Our task, if we wish to plan for an efficient future, is to implement the most efficient forms of transportation that people will actually choose. Building a system that would be efficient if people rode it, but which people won’t end up riding is not the green thing to do. It’s actually anti-green.

And yes, the bus does stop running if people don’t ride it, at least if the bus system is rational. No single rider or non-rider makes that happen, but in aggregate they do. Many bus systems are not rational of course, they don’t even go so far as to run a smaller, lighter van as demand drops.

Of course cars should be measured on their occupancy. That’s what the transit is judged on. But your argument that we must add the energy of the bus we didn’t ride to the energy of what we did ride makes no sense to me. This is not about individual rides, it’s about how to plan what to build.

Yes, roads do use more energy to build and that is a factor I would like to get good numbers on to include in calculations. And yes, buses should definitely be hybrid and perhaps some day they will. But cars, as they go electric and hybrid are getting better even faster, due to the greater rate of innovation you always see in small personal products compared to big institutional ones.

But my main difference is your attempt to disparage my motives. My goal is to try to figure out what we can make efficient based on what people will actually use. Many seem to come into this saying, “transit is clearly better, and if it’s not efficient enough, let’s try to force it to be.” I think we should end up deciding what is better by factoring in the final results, and not just the theory. Right now, based one what I know people want from their transportation, the robot cars, once implemented, offer the best combination of meeting that demand and being efficient, though even that is not assured. Transit’s long history does not predict much success here. The history of cars would not either, if it were not for the fact that now people are looking to buy more efficient cars, cars 2-3 times more efficient than what they had a few decades ago.

Will we ever get transit ridership and service in the USA to match that in places like Japan? Past history indicates not, but even the fine Japanese transit doesn’t beat the potential of ultralight cars as enabled by robotics.

Other figures to contemplate

Noah — Sat, 03 Jul 2010 01:05:19 -0700

When we choose to drive, we are adding our car to the existing transportation modes in operation. Jumping on the bus doesn't add significantly to the fuel consumption of the bus, but it will run whether or not we get on.

Therefore, the BTU's per PM figure for a car should be added to the figure for the bus, train, or other option not chosen, like this:

1. Bus --4300 BTU/PM
2. SUV + Bus --8200 BTU/PM
3. Electric car + Bus --6400 BTU/PM

It's not as if we can cause the bus to stop running by not riding it. We can only choose not drive our own car.

Another concept to consider is the efficiency of highways vs. train tracks. For medium-distance rail from suburbs to cities, the trains use only a set of tracks which require very little maintenance over many years. Cars require a highway with 2-4 lanes on each side, the surface of which needs to be periodically replaced at a huge expense.

It seems to me that in your effort to promote robocars you've done a disservice to mass transit modes by selectively using the statistics and underplaying the value of increased ridership and economies of scale. Recycling plastic, for example, is inefficient on a small scale, but at a certain critical point it becomes profitable. It would be more so if the environmental cost of plastic were embedded into it's retail cost.

City buses would benefit from hybrid technology, which would mitigate the inefficiency of their frequent starting and stopping.

I think your use of the 1.57 passenger average figure is misleading. When most of us make a commuting choice, it is not with 1.57 people in mind, but simply ourselves. Your figures for car efficiency should be based on 1 single passenger. There is no such thing as 1.57 passengers. If and when we consider taking another passenger along with us, then we can simply make our decision based on nearly doubling our efficiency, etc.

But again, that is subject to the fact that the bus or light rail would run with or without us, so we must add our car's energy use to that of the bus.

It seems to me that you've gone out of your way to trash mass transit. The fact that you've ridden it or your bicycle doesn't absolve you of that.

The very same stats can be interpreted to show a brighter future for mass transit, and I think it would help our country more for you to use your considerable researching skill and efforts to that end.

Is Green U.S. Transit a whopping myth?

brad — Mon, 09 Jun 2008 20:11:22 -0700

As part of my research into robotic cars, I’ve been studying the energy efficiency of transit. What I found shocked me, because it turns out that in the USA, our transit systems aren’t green at all. Several of the modes, such as buses, as well as the light rail and subway systems of most towns, consume more energy per passenger-mile than cars do, when averaged out. The better cities and the better modes do beat the cars, but only by a little bit. And new generation efficient cars beat the transit almost every time, and electric scooters beat everything hands down.

I encourage you to read the more detailed essay I have prepared on whether green U.S. transit is a myth. I’ve been very surprised by what I’ve found. It includes links to the sources. To tease you, here’s the chart I have calculated on the energy efficiency of the various modes. Read on, and show me how these numbers are wrong if you can!

I have added a follow-up post on the comparison between lots of small personal ultralight vehicles and larger shared transit vehicles.

Note: If you want to comment on the cyclist figure, there is different thread on the fossil fuel consumption in human food which details these numbers and invites comments.