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Someone who is opposed towards energy saving and climate change (I did not realise they existed until I met him) has told me that public transport (buses, trains and so on) are less efficient than individual cars.

I found it difficult to believe. A bus is very big, but it can hold many people. A car could carry maybe 5 people maximum and usually, when commuting only one or two people will come. A bus could hold 30 or more. That means that an average car doing 35 mpg would only be better if a bus did about 1.2 mpg, which I find difficult to believe. I don't know about trains, though. This is also assuming the bus is full which it might not be, but probably is most of the time, especially during morning commutes, in my experience. Maybe not all day, though.

Is this guy lying to make a point, or does he actually have a point?

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I don't have statistics on this... but he might have a point. My municipality runs a fleet of busses throughout the city, all-day, every-day. They're almost always empty. My last "city" (much smaller) did the same with about a dozen buses. I rode them there, and at least half the time I was the only one in the bus. –  user73917 Jun 20 '11 at 15:59
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I find it difficult to take anyone who is actively opposed to energy saving seriously. I can see "indifferent", but opposed? However, he is right under some circumstances. As you mentioned, capacity is the key, but I think your assumption that buses and trains are full "most of the time" is inaccurate. Mass transit needs to maintain a certain occupancy level to maintain efficiency. Whenever they operate below that level they are less efficient than cars. –  Beofett Jun 20 '11 at 15:59
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I disagree with "not taking one seriously" solely on the basis of his claims sounding ridiculous, it's certainly not the mindset of a skeptic; I would certainly listen to his arguments, and then decide whether to take the guy seriously or not. Also, there's no logic connection between climate change and public transport efficiency - he might be wrong about one, but he might very well be right about the other. –  Mihai Rotaru Jun 20 '11 at 17:00
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It seems to me all data presented here so far are US based. I think European data would give a very different picture, as public transportation in Europe seems to be used a lot more than in the US. –  Suma Jun 20 '11 at 19:31
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@Suma: I think Hong Kong or Tokyo would be even better. –  Neil G Jun 21 '11 at 6:32

9 Answers 9

Yes, public buses appear to be worse than cars, at least based on the data I found for the US. (At present and on average. See the "Caveats" section for a discussion about this.)

Edit: the answer from DJClayworth appears to be based on the same information, I just noticed. bbc.co.uk just links to the overview for the Dept. of Energy report, but doesn't break things down.


Update: I used data from National Transit Database (LINK) to calculate BTUs/passenger-mile for every US city. I was initially unsure of how to do this, but I just wasn't looking at the right documents. The data I used is available in the bundle of Excel files titled, "RY 2009 Data Tables - Complete Set (Self-extracting xls)" (LINK). The necessary files are "T17_Energy_Consumption.xls" and "T19_Op_Stats_Service.xls." From these, I was able to compare fuel used to passenger-miles traveled for all buses in the country. The results are as follows:

Passenger-miles for buses in the US

The Excel files above list all public transportation by type, so I sorted and pulled out all bus listings, then summed the listed passenger-miles for each state. I also used the conversion factors mentioned below to convert all of the fuel listing into BTUs and then simply divided BTUs by passenger-mile to find the rates. I used the value of 3,400 BTUs/passenger-mile as listed below and inserted "Car" into the chart. It appears 6th in the list; in other words, only five US states have achieved an efficiency higher than a car for transporting individuals.

See below for discussion about BTUs

I left the rest of the answer mostly as it was -- it jives fairly well with this data, other than the bus average coming out to about 5,000 BTUs/passenger-mile with the National Transport Database data vs. the Department of Energy value below of 4,300.


Data/Analysis

Data to attempt to answer this question may reside in The Transportation Data Energy Book, published by the US Department of Energy (DoE). We will be pulling from Edition 29, published in June 2010 (available HERE).

Table 2.12 is shown here (LINK): Table 2.12 All Vehicle Statistics

To highlight the pertinent values for 2008:

  • Cars: 137 million cars traveled 1.6 quadrillion miles for a total of 2.6 quadrillion passenger-miles, and consumed 8.8 quadrillion BTUs of energy to do so.
  • Buses: 67,000 buses traveled 2.4 billion miles for a total of 21.9 trillion passenger-miles and consumed 95 trillion BTUs of energy to do so.

Passenger-miles are a summation of (passengern * milesn) for all passengers (1 passenger mile = 1 passenger travelling 1 mile, 2 passengers travelling 0.5 miles, etc.).

The key value is BTU/passenger-mile:

  • Cars: 3,437 BTUs/passenger-mile
  • Buses: 4,348 BTUs/passenger-mile

This means that, on average, it is taking buses more energy than it takes cars to transport a given number of individuals a given amount of distance.

By using BTUs, fuel types are normalized by converting to energy per volume. See Table 2.5 in Chapter 2 (LINK) for a breakdown of fuel type usage by vehicle type. Also, Appendix A (LINK) provides the conversion factors for different fuels to BTUs.


BTU Discussion

The British Thermal Unit is a unit of energy. Analogs would be the calorie and the joule. Thus, the Department of Energy has taken each fuel type and translated it to an energy per volume output. Thus, if we know that a gallon of fuel X outputs Y BTUs, and we know the average number of BTUs required to move vehicle type Z a given distance, we have an efficiency value for each type of vehicle that has been normalized from fuel type to energy. Then we can analyze the energy required to transport a vehicle with it's typical passenger load (9.2 passengers per vehicle for buses, and 1.57 passengers per vehicle for cars) and determine energy per "passenger-mile."

We want a lower value here, since lower BTUs/passenger-mile means that it takes less energy to transport a given number of passengers a given distance.


See Table 11.11 in Chapter 11 (LINK) for a breakdown of emissions by fuel type. Buses primarily use diesel, while cars primarily use gasoline; the emissions for these two aren't all that different, with diesel at 10,000 grams/gallon emitted and gasoline at 8,800 grams/gallon.


Caveats

First off, this is only US data. I have no idea how the rest of the world compares.

Second, this is a snapshot. If buses were to increase their average "load factor" (persons/vehicle) such that their passenger miles were 30,000, they would be more efficient than cars on average. If buses reduced their BTU consumption, this would also help a great deal (I was blown away by the fact that buses require almost 8x the BTUs to travel 1 vehicle-mile compared to cars and 7x for trucks). Now, this is the data for all buses in all cities in operation. Thus, there are probably some cities doing quite well, while others are doing horribly. This paper abstract seems to confirm the same (emphasis mine):

The simulation results show that substitution of bus for car travel generally decreases the overall costs, particularly the costs of congestion, but increases exhaust emission costs if bus load factors are insufficiently high. In order to reduce exhaust emission costs from car to bus transfer at given load factors, the most effective policy option is to encourage the reduction of particulate emissions from bus engines. In terms of the overall costs, increasing bus load factors by relatively modest amounts can lead to substantial reductions in these overall costs. (SOURCE)

So, it seems to depend on the usage efficiency of the vehicle. I also note that the rail figures in Table 2.12 shows that "rail" travel does better than cars, so whatever circumstances are surrounding that mode may be of interest.

Lastly, suggested by @Ian, is that this comparison doesn't take into account the travel by individuals to the public transport departure location. This could be neutral in the case of walking, but it could be optimistic if folks are driving cars to a pickup location.

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This data is only for U.S. cities, I would expect the data to be quite different for European or Canadian cities. For example, in Vancouver, most of the buses are powered by electricity. –  Lotus Notes Jun 20 '11 at 20:46
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A much bigger caveat is that there is no reason to assume that it would be possible to replace public transport trips with efficient car trips. People who are electing to take public transport to avoid high congestion, for example, cannot drive and expect it to be 3.5kbtu/mi. –  Neil G Jun 21 '11 at 6:25
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While this is a worthwhile answer, the points I'm making are that you cannot conclude that it would be a savings to remove public transit and replace it cars, nor is it a savings to avoid public transit. For a study that could make that kind of conclusion, you would have to do a proper experiment whereby you essentially force everyone to drive instead of using public transit and check the difference in energy consumption. We have these experiments: they're call transit strikes by some people. Other people call them traffic jams. –  Neil G Jun 21 '11 at 6:30
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"rail travel does better than cars, so whatever circumstances are surrounding that mode may be of interest" - Rail links are installed on high-demand/high-density routes, where the demand (number of passengers/hour) is so high that it can't be satisfied by buses (e.g. order of magnitude of 1 bus/minute). Under those circumstances (high demand => high occupancy) no wonder it's efficient. –  ChrisW Jun 21 '11 at 12:46
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It also needs to be pointed out that this doesn't mean you're polluting more if you take the bus rather than use your car - you're polluting much less. –  DJClayworth Jun 22 '11 at 13:54

David JC MacKay's excellent book Sustainable Energy - without the hot air (free ebook), has a nice chapter on public transport.

At its best, shared public transport is far more energy-efficient than individual car-driving.

  • A diesel-powered coach, carrying 49 passengers and doing 10 miles per gallon at 65 miles per hour, uses 6 kWh per 100 p-km (passenger-km) – 13 times better than the single-person car.
  • Vancouver’s trolleybuses consume 270 kWh per vehicle-km, and have an average speed of 15 km/h. If the trolleybus has 40 passengers on board, then its passenger transport cost is 7 kWh per 100 p-km.
  • London underground trains, at peak times, use 4.4 kWh per 100 p-km – 18 times better than individual cars.
  • Even high-speed trains, which violate two of our energy-saving principles by going twice as fast as the car and weighing a lot, are much more energy efficient: if the electric high-speed train is full, its energy cost is 3 kWh per 100 p-km – that’s 27 times smaller than the car’s!

However, we must be realistic in our planning. Some trains, coaches, and buses are not full (figure 20.6). So the average energy cost of public transport is bigger than the best-case figures just mentioned. What’s the average energy-consumption of public transport systems, and what’s a realistic appraisal of how good they could be?

In 2006–7, the total energy cost of all London’s underground trains, including lighting, lifts, depots, and workshops, was 15 kWh per 100 p-km – five times better than our baseline car. In 2006–7 the energy cost of all London buses was 32 kWh per 100 p-km. Energy cost is not the only thing that matters, of course. Passengers care about speed: and the underground trains delivered higher speeds (an average of 33 km/h) than buses (18 km/h). Managers care about financial costs: the staff costs, per passenger-km, of underground trains are less than those of buses.

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It would be nice if you could summarize what the book says about the topic of this question. –  Fabian Jun 22 '11 at 9:29

First of all, public transport is not just buses. In fact buses are the least efficient. Metro (aka subway) and electric trains and trams (streetcars) are more efficient and can use green power. For example all of Amsterdam's trams run on green power.

Even if you're talking buses, they can run on all kinds of green fuels, as they don't usually depend on random gas stations. There are buses running on ethanol, on hydrogen etc.

Also while comparing MPG you have to take in account huge difference in MPG in urban cycle, mixed cycle, and highway cycle. Buses ride mostly in the cities, while 20-something MPG for cars quoted above "assumes 55% city and 45% highway-miles". Difference between urban and combined with car is about 20-40% more fuel burned in the city. Thus 20MPG in combined cycle translates to something like 14-16MPG in urban cycle.

Talking about massive transport we should also include air transport. Airbus A380 has fuel efficiency of 2.9L/100km per passenger (that's 82 passenger-miles per gallon).

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Here is an interesting article that seems to back up your friend's claims. The article says that bus occupancy is about 9, and car occupancy about 1.57, and cites a study that buses are more polluting than cars at these figures.

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done the math myself years ago and came to a similar conclusion, not just for busses but trains as well. –  jwenting Jun 22 '11 at 12:57
    
Apart from the occupancy: bus routes are usually not as straight as car routes would be. And most trips can be done by using a bicycle ;) –  johanvdw Sep 27 '11 at 7:42
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It is interesting to note that cars are only as efficient as they are because of the number of people who use public transport, given that the passenger density of public transport is so much higher than cars. Even using your occupancy figures of 9 and 1.57 then you would need at least 5 cars per bus. Given that 5 cars will take up at least twice the road space of 1 bus, the extra congestion of a doubled road space required would push car fuel efficiency way down. And that's not considering what would happen at peak time, when occupancy is much higher. –  Mark Booth Sep 27 '11 at 10:56
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@johanvdw Here in Canada we have bus routes that go for thousands of km. Good luck doing that on a bicycle. –  DJClayworth Sep 27 '11 at 14:11

Other answers have shown evidence that public transport, particularly buses, is less efficient than car transport.

However, from the data, it looks like this is due to the buses being under capacity. They are inefficient compared to cars because they are much bigger and use more fuel while only providing transport for a few more people. From the table:

table

Transit buses provide an average load factor of 7.61 people/vehicle more than cars. Their energy use is much higher such that for these load factors, it is less efficient to use bus transport.

This isn't really a fair comparison because both vehicles could take more passengers. It is known that vehicles are most efficient per passenger when they hold the maximum number of passengers they can. This is because the extra energy cost of adding a person to a vehicle is much less than having another partially filled vehicle making the same journey.

To make a proper comparison, we would need data for the Btu per passenger mile for each vehicle used at its maximum capacity.

So this person isn't lying as such but the way he is using the data is misleading. The data used is based upon inefficient use of transport. If more people took the bus, the buses would become more efficient (a lower Btu per passenger-mile) and it would eliminate extra cars which themselves are currently expending energy.

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You're saying "if more people took the bus" might be wishful thinking, and is not obviously evidence that "the way he is using the data is misleading". –  ChrisW Jun 21 '11 at 14:21
    
I don't understand. How is it wishful thinking? –  david4dev Jun 21 '11 at 14:25
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More people don't take the bus. The question is about whether they are less efficient (now, presumably); not about whether they would be more efficient if more people took the bus (enough 'more' people, presumably, to fill the buses and to therefore make them 'efficient'). –  ChrisW Jun 21 '11 at 14:30
    
Well I suppose, but generally these arguments are used to support some sort of action - namely moving to using cars more or buses more. I'm saying the claim is misleading because I perceive an implication of "so we might as well continue with/increase car use". –  david4dev Jun 21 '11 at 14:35
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@david4dev: I agree that mass transit definitely has the potential to be more efficient... but (as I've said numerous times in my own answer), at present and on average, it's not. In any case, I guess I found it odd that you would use my own picture (I uploaded to my imgur site) and write this up into an answer -- why not just a comment suggesting comparing max loads for both modes? –  Hendy Jun 21 '11 at 14:48

Yes, individual buses are ridiculously less efficient than cars. A Santa Barbara study (link blatantly stolen from Wiki) showed them to have a MPG rating between 4.8 and 6.0. This is obviously far worse than even the evil hummer.

Cars average something in the mid-20s MPG (according to bts.gov). In order to be more fuel efficient than individual cars, buses need to be carrying on-average 4-6 cars worth of people. I'm not finding any good statistics on the average number of people per car in US cities, and that's obviously needed to determine the "break-even point" for buses.

You also need to factor in the movement of the bus from parking spot to its route (not an issue for individual's cars), and include that time in the "average" vs the number of passengers.

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@user73917: Yes... you've shown the MPG, and hinted at how many people they need to carry... but you haven't gone the last step and shown how many people, statistically, ride on buses throughout the day. Without all the pieces of information, we can't answer the question. –  Hendy Jun 20 '11 at 16:25
    
@Hendy: That's because it's fairly obvious that you can't generalize this. Different cities will be wildly different here. My city (~130k pop) is definetely on the losing end here, I've never seen more than 8 people on a bus. I can pick a few cities and show that it's more efficient in SanFran (something I'm fairly certain of), and roughly a wash in MSP (not sure on that one), but there isn't "an answer" to this question. (just a formula to apply to your particular city) –  user73917 Jun 20 '11 at 16:30
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What you see (one pair of eyes at an extremely small sample rate) is different from the statistical characteristics of this. –  Hendy Jun 20 '11 at 16:38
    
@Hendy: That's why it's a comment, not in the answer. (if I gave it as an answer, it would also be 'too localized') If you have any meaningful suggestions or actual data to fill in any of the variables that I mentioned, feel free to share them. –  user73917 Jun 20 '11 at 16:41
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@user93717: My suggestions have been meaningful -- you just didn't have the data necessary to implement them. My answer now contains the data to answer this question, at least on average and at present ("on average" in that I agree with you that certain cities are probably more efficient and others are horrible, and "at present" in that in 5 years things may change and the picture may look better for public transportation). –  Hendy Jun 20 '11 at 19:35

I'm just adding one more source to the mix: http://www.delijn.be/over/milieu/co2_uitstoot_verkeer.htm

It is in dutch, but some highlights:

  • avg traffic: 118 g/km
    • bus (14 persons): 85 g/km
    • tram (23 persons): 23 g/km (nuclear power)
    • train :28g/km

But do these numbers mean that adding new trams and trains will lower CO2 usage? Not necessarily:

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This page with 2010 statistics for Toronto's public transport includes ...

  • 124 million km by bus
  • 477 million passengers (total: by bus and subway)

If you assume that each passenger rides the bus for several ('x') km on average, that implies an average of approximately 4'x' passengers per bus (or actually a bit less because some number of those passengers only take the subway and not a bus ride).

I have to guess: and my guess is that this 'x' is greater than 2 (km per average passenger trip). The "Table 1.2" shown in other answers suggests you need an average of 11 passengers/bus to break even with cars (measuring fuel/passenger/distance), and therefore it seems to me that the TTC might break even on that metric.

Fuel consumption for a (unloaded) bus is relatively high (buses are neither light-weight nor aerodynamic, and outside the stop-and-start of the down-town core, expensive hybrid technologies like regenerative braking result in fuel economies of only about 10%).

It seems that the TTC doesn't publish and perhaps doesn't even collect statistics on passenger-miles: they'e only/mostly/more interested in vehicle miles, number of fares (passenger trips, not passenger distances, because fares are fixed-rate and distance-independent), and vehicle occupancy when and only when the occupancy get high enough to require scheduling more vehicles (in rush hour).

Outside of rush hour they are scheduled to provide convenient service (e.g. bus routes having service 4 or 5 times an hour throughout the day and into the night as well, and not only during rush hour), even when occupancy is low.

Two points to note:

  • For each new passenger, it is 'greener' if they take the bus: because, the bus is running anyway.
  • This communication published by the City of Toronto (which doesn't reference the source of every statistic, and which is written by an city counsillor who is an "environmental activist") says of public transit that we "we couldn't afford to do without it", according to a dozen or more other metrics (economic, social, and environmental).

On its page 11, Marilyn Churley's report cited above says, "average bus occupancy is about 20 people": but without explaining that figure. For all I know, that figure might be rush-hour-only: but if so that wouldn't be the first time that some expensive system is engineered to cope primarily with peak demand (it's ditto electricity generation, for example).

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Summary: one way in which people justify public transport is for how well it copes with and how necessary it is in helping to cope with peak (rush-hour) demand - the average occupancy might be so-so, but the peak occupancy is tremendous and (in the bigger cities) indispensable. –  ChrisW Jun 21 '11 at 13:54
    
Public transit is also provided for the same reason as many other public (government-sponsored) services are: because it provides social benefits, even "uneconomic" benefits (in a similar way that, for example, schools are subsidised by general taxes and not just user fees). –  ChrisW Jun 21 '11 at 14:02
    
yes Chris, but it's SOLD as being "clean" and that that's the reason we should use it. –  jwenting Jun 22 '11 at 13:09
    
@jwenting It's 'sold' for a number of reason but here I say how much fuel you'd use if you took public transport instead of your car. –  ChrisW Jun 24 '11 at 4:50

Is this guy lying to make a point, or does he actually have a point?

It's difficult to know what his motive is (and if he does have a point then it's probably better if he expresses it than me).

The question is misleading, in various ways.

If you limit the discussion to only fuel efficiency, more relevant than average fuel efficiency is the incremental or marginal cost: for various (other, sufficient) reasons the buses are running anyway: so if you make a trip via public transport that uses no extra fuel; whereas if you take a private car that does use extra fuel.

Your using public transport increases total fuel consumption only at peak/rush-hour times (i.e. if you contribute to the bus being so full that they need to supply an extra bus). Note that this (peak/rush-hour utilization with full-buses) is exactly the time at which buses are actually more fuel-efficient per average-passenger-mile than cars.

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If a bus with an available seat happens to be going where one wants to go, when one wants to go there, taking the bus will clearly be more energy efficient than taking a car. On the other hand, if in the course of the day a bus is used by relatively few people, most of whom have cars, having those people either drive themselves or take the taxi might consume less energy than running the bus. –  supercat Jun 3 at 22:38

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