by Mike Bjork

The FTA has a new (January) report on carbon footprints of various transit modes, based on 2008 data.  For electric transit, the authors use estimates based on the composition of that region’s power grid.  Here are the locally relevant figures:

System lbs. CO2 per passenger mile
Washington State Ferries 2.123
Seattle Streetcar 1.301
Avg. U.S. SOV 0.964
Metro Diesels 0.452
[Tacoma] Link 0.411
Metro trolleys 0.388
Sounder 0.369
ST Express 0.327
King Co. Vanpools 0.246
Snohomish Co. Vanpools 0.239
Pierce Co. Vanpools 0.228
Seattle Center Monorail 0.190

For comparison, the Portland MAX, a more mature system, comes in at 0.213. The national champion is Maryland’s MARC commuter rail at 0.013.  Of large systems, BART (0.085) is very efficient with particularly clean energy.

Thoughts below the jump.

  • What’s missing here is the extent to which certain transportation types  encourage density and walking, thus reducing passenger miles and overall carbon impacts.  That’s difficult to measure but important to remember.
  • Considering Link’s partial implementation and relatively undeveloped corridor, it is doing pretty well and will probably be in the ballpark of MAX when built out. [This 2008 data of course refers to Tacoma Link.  No more late night edits!]
  • For some of these modes, the marginal cost of a new rider is zero; those modes will be better at sustainably accommodating growth.
  • King County’s vanpool system is second in size in the nation (!), behind only Utah Transit Authority.  It serves 6.2% of all vanpool passenger miles in the nation.

Via Huy Le of Green Growth Cascadia.

103 Replies to “Carbon Footprint of Transit”

    1. Average load factor is why. The typical Metro bus has only 11 or 12 passengers per platform mile. The Streetcar is probably only 3 or 4 people. So much for energy efficiency of Streetcars!

      1. But wouldn’t that same effect be noticeable on the monorail? It’s not jam packed full of tourists all the time! :-)

      2. I had been wondering the same thing. Is it so spectacularly energy efficient that it comes out great, or is there an infrastructure term that’s been discounted away for the monorail because it’s old enough?

      3. Sure it’s not the carbon cost to dig the tunnels for LINK? These tunnels are huge energy costs that will take years to balance out their worth in carbon.

        That said, tunnels are a good way to gain extra transit corridors and leave the surface to walking & bicycling.

      4. Wells: that was a spectacular tangent from a question about the monorail system that we already have.

        Gary: thanks for mentioning that; it’s a good point.

      5. I’m guessing number of stops has a big effect. Once rolling energy output is a small fraction of what it takes to accelerate. The SLUT has not only multiple stops for passengers it gets stuck at red lights.

      6. I suspect the old Waterfront Streetcar probably had better numbers than the SLUT and I’m willing to bet the First Hill Streetcar will have better numbers than SLUT.

        Of course if SLUT’s ridership goes up it’s carbon numbers will improve as well.

      7. And this is from 2008 when it just opened. It’s numbers have gone up a lot since then and continue to increase all the time.

      8. I think the energy data are from 2008, but the ridership data must be more recent, since Central Link is on the list.

      9. I don’t think the riderhsip data is more recent. Link numbers are probably from Tacoma Link light rail.

      10. Yes, you’re probably right. The report says “Source: Calculated from Federal Transit Administration 2008 National Transit Database (NTD)”.

      11. That’s a ridiculous statement. The South Lake Union Line has a high carbon-footprint because there is not enough density yet to fill up the cars. It has nothing to do with streetcars in general. If it went all the way to the U District, you can bet the cars would be packed and it would score higher. Over time more people and jobs will move into South Lake Union as well. The First Hill streetcar will be much more successful from the very start, and will be very low-carbon.

    2. I bet Link’s long and relatively lightly-passengered (compared to other Link legs) section from Rainier Beach south has something to do with it – fewer passengers on that one long part makes anything per passenger mile higher.

      The monorail, by contrast, is really short, and has a lot of times when it’s insanely jam-packed. Link gets packed also, but less so in its long southern section, I think.

      1. That would make sense. Lake Union Streetcar and Tacoma Link are similar in length. However, Tacoma Link has more frequent service and 3 times the ridership of SLU in 2008. That’s likely why SLU’s CO2 per passenger-mile is three times more than Tacoma Link’s.

  1. The marginal cost is key. For each additional person that gets on the streetcar or light rail the additional CO2 is near zero. They also will run regardless of any one individuals choice whereas a car will not.

    1. It’s still a math problem where you divide the CO2 footprint by everyone on the train – otherwise, the first guy to get on would have a pretty monstrous carbon footprint!

      1. You really should divide the CO2 output by everyone who has access to the train. The riders are irrelevant to the output.

        If I turn on my car and go for a drive I have increased the output of CO2. The same does not happen if I get on a train. The two really are not comparable when you think about it.

  2. I’m really not surprised about WSF. I’ve been saying for quite some time that we need to raise car fares for the ferries, decrease passenger fares and remove car ferries where possible and substitute them with passenger-only ferries. I bet we could significantly reduce the passenger per mile CO2 emissions, but I’m not sure if WSDOT has the stomach to do the hard, but right thing here.

    1. Something to consider with the high CO2 per passenger mile for WSF is that the trips are shorter/more direct than if those automobile trips occurred on highway routes. If that was accounted for, WSF probably wouldn’t look as bad.

      1. Plus walk-ons, who don’t drive to and from the ferry dock, would probably have to drive around were it not for the ferries.

      2. You are correct, if comparing journey to journey, which I don’t think the report tries to do at all. On the other hand… I’m wondering how comprehensively this analysis takes infrastructure into account. For the ferries, there are two big issues to compare with SOVs:
        – on the one hand, how much west-of-the-sound development and cross-sound commuting is only possible because of them (from Martin’s original post we know that wasn’t included)
        – on the other, what the carbon cost of building a bridge would be. Obviously that specific cost is not included, and would be outrageous, but does the car emissions figure include a general estimate of car infrastructure costs per passenger mile?

      3. I should have mentioned that point. But it’s also essentially a moot point because I think you’ll be hard-pressed to find many willing to drive from Bainbridge or Bremerton to Seattle on a daily commute. But who knows, I could be wrong. Neglecting ferry-dependent islands, (save for perhaps Vashon), I don’t think there’s anything wrong to suggest that we should restrict car ferries. Upping prices for cars to the point where it is a complete disincentive to drive on the ferry on a regular basis is a positive thing. It forces people to live closer to where they work such as on Bainbridge, Bremerton, or Whidbey. Under the assumption that people wish to remain in these communities and commute to Seattle, it would necessarily mean that cities become even more compact and that residents become foot passengers; meanwhile, reducing car ferry usage to largely leisure trips only. Walk-ons are grand.

      4. To which the Car people will say build a bridge across the sound. Then what will you say?

      5. Oh, I wish it were so, but sadly there is a lot more commute drive around than folks might admit. My day job includes a lot of folks who cannot afford to live within the city limits. I am the rare bird with a metro only ride home. About half of my coworkers live in Pierce or Snohomish county, and the third largest contingent commutes from Bremerton. Ferry is great, but often the drive round is just as quick and with 3 or more aboard the car pool, in summer cheaper than the WSF.

        The laws of physics vs. the capacity vs. demand. Bigger boat, more fuel used. Higher expectation (22 knots home vs. 9 knots) and you can get into quite the balancing act. Toss in a headwind, or tide, and you can toss the grid goodbye.

        The crossound bridge idea has been around since the 30s, and even the huge worker build up at PSNS during WWII, the concept made little sense. There have been hydrofoils, hover craft, and vessels of all sizes. There were even legit plans to look at pneumatic tubes.. SO far the numbers continue to prove the wisdom of what we currently have and what we hope to build. Until you compare journey to journey, it will always look bad.

      6. The large car ferries already do 20 knots. According to WSF they can’t raise rates or they’ll loose money because of people choosing to drive around instead. I’m not convinced that’s true. Our motivation to drive around from Kingston is more often than not the two hour wait on Sunday evenings. A simple peak demand fare system would raise revenue. Obviously there are boats that are going to run full where the increased fare will be 100% increased revenue plus I think there will actually be more demand because you’ll know that you’re wait will be one boat or less; you just have to be willing to cough up the extra dough to travel at the prime times.

        I really doubt simply pricing cars out of the market is going to be matched by increased passenger revenue. Plus, the car ferries are funded in part by the gas tax because they’re considered part of the highway system. A shift to passenger only would require more transit designated tax revenue and Kitsap is already tapped dry. Add on to that they’d have to provide more public parking and/or more buses to access the ferry and I think it’s pretty clearly an unworkable ideal. The Puget Sound is a natural buffer to sprawl; why fight it with higher taxes?

      7. I see your point alright. Just to add fodder to the fire. I wouldn’t be concerned about it losing money to subsidise passengers only. They aren’t really my beef.

    2. I’m not sure just how much passenger-only service would improve things. The thing is, passenger boats are lighter, but they also move faster and that makes a big difference in the fuel consumption of watercraft (drag is proportional to speed squared — you can make water transport about as efficient as you want if you’re willing to move very slowly).

      The other thing to consider is that the marginal CO2 footprint of moving additional passengers on an auto ferry is negligible, whereas running additional passenger ferries will increase emissions, unless you actually do reduce the number of auto ferries. I don’t know if that would happen.

      WSDOT won’t do this because they can’t dedicate gas tax money to passenger ferries and the state isn’t going to set aside other money for this. That said, I wonder if they could cover the auto ferry service entirely with gas tax money and use the fares from auto ferry service to subsidize passenger-only service? I doubt they would.

      1. Well passenger-only would be more efficient hands down. I imagine if they parsed out the Seattle Water Taxi it would be less than 1.0. Remember, per passenger. 1 car = at least the equivalent of 8 passenger seats and you can be guaranteed that most cars aren’t filled.

      2. It’s really hard to get passenger only ferry service going since WSDOT gets sued everytime they do so. As I recall Bremerton/Bainbridge residents sued because the wakes of the faster passenger ferries were “damaging” their shorelines. In addition, the ferry system has some powerful political support. Mary Haugen has both the Keystone-Port Townsend as well as the Mukilteo-Clinton runs in her districts. The ferry sytem is such an iconic symbol of the Puget Sound that it is unlikely that it will be abolished. Private industry can’t afford the fares which passengers would demand.

      3. Never suggested to abolish the ferry system. I would say that would be an unwise move. I was suggesting we look at how we operate it and make some significant changes. I think Bernie has some interesting insights on it too.

      4. “drag is proportional to speed squared” Right, but drag is also proportional to wetted hull area. The wetted hull area of a car ferry is huge compared to a passenger-only ferry. Besides, we could run the things as slow as car ferrys and still speed up the trip, since we don’t have to wait for cars to load and unload.

    3. How do you know that a passenger ferries carbon footprint is lower? Maybe it is the mode of travel at play here.

      1. It has to do with the numbers of passengers and to an extent class of watercraft. Passenger ferries have a higher number of passengers per square foot than a car ferry. They also don’t have a crap load of weight coming from cars. That necessarily implies less CO2 emissions per passenger mile if the ridership is decent enough.

    4. I would guess that it would be hard to get passenger-only ferries built where there’s little transit for them to connect to on either end.

      Which ferry routes are the most natural targets for passenger-only ferries? You’d be looking for:
      (1) High density near the ferry terminal on both ends;
      (2) Rail stations near the ferry terminal on both ends. Oh, that doesn’t happen, does it. How about a bus hub with lots of frequent bus lines on at least one end, then?

      1. Pretty much narrows it down to Alki to DT Seattle. Thing is, buses are still way more efficient. It’s a nice tourist run but it doesn’t help Metro at all in providing regional mobility; in fact it’s a drain on resources. Tack on that ferries are hands down the biggest polluters and they’re all just a bad idea.

        The possible exception is Vashon to DT Seattle. That’s because the alternative was a car ferry. The stupid is better than the absurd. We’ll fund a “brokers special” from Vashon because a car ferry would be even worse. To paraphrase, “What a county!”

  3. Aren’t the streetcars and some of the other transit modes electric? If they’re getting power from hydroelectric dams, they’re theoretically not releasing any CO2 (aside from initial construction of infrastructure and creation/delivery of vehicles). Are these FTA calculations for CO2 assuming that all power comes from fossil fuels and therefore produces CO2?

    1. “For electric transit, the authors use estimates based on the composition of that region’s power grid.” Sounds like they take that into account, although to what degree?

      Hydroelectricity, while renewable, is not without a carbon footprint. Besides the capital “expenditure” of carbon you mentioned, there are four ways hydroelectric generation can result in a net increase in greenhouse gases that I can think of for the Northwest. They are emissions associated with dam operations, such as trucks driving around Marblemount and Newhalem, the destruction of a large carbon sink in the forest that was flooded to make the reservoir, increased decomposition in the reservoir, and decreased solubility of gases like CO2 in the warmer, stagnant reservoir water compared to a river (this last one’s impact is negligible).

      1. I would just add that the amount of CO2 attributable to hydroelectric generation, while certainly not zero, is exceptionally low, so the numbers in the table remain a little hard for me to get my head around.

      2. It’s because hydro only supplies part of the regional electricity demand. They took the regional average of which about a quarter is generated by coal.

      3. …which is especially dumb for the Streetcar as those are City Light power lines and City Light is about 90% hydro, 4$ nuke, and 3% wind. That 3% of other sources is not generating that carbon footprint.

        And usually on the Streetcar, which i ride about 4x a week, there are at least 7-10 other people at worst, 20-25 at best. I’m not buying it, though i am buying the WSF numbers. Those ferries burn a lot of diesel!

      4. As far as I know those sources of carbon aren’t really factored into these FTA numbers. The dam construction itself also is a major carbon source, just like plant construction is a major contributor to the lifetime carbon emissions of a nuclear plant.

      5. Looking at the report really makes me wonder. It could be clearer. While they do have something that factors in the grid, the pie chart in the first figure distinctly separates transportation from electric power generation.

    1. Does anyone know where the FTA gets its carbon numbers for electric transit? Is this a national or regional average rather than the fuel mix used by a particular utility?

      1. Each region of the U.S. gets a different “Pounds CO2/MWH for eGRID subregion.” So it’s not a national average, but I can’t yet wrap my head around exactly where that number comes from.

      2. Probably from the EPA website that lists cities energy mix. Seattle shows up at about 55% clean energy, as I recall, but City Light numbers are much better. About 98% clean. Way to go city light.

      3. I believe City Light has the goal of becoming the first fully carbon neutral utility in the US. Of course that is a bit easier to do when you have such large hydro resources and some unusually reliable wind power to purchase.

      4. If that is the case, which would make sense, it’s interesting they used the EPA number for Seattle yet used a number provided to them by BART instead of the subregion value. Using a number that applies to a subregion is probably not as fine a resolution as City Light only.

  4. Honestly, I’m surprised the Sounder numbers are so low. Those things are dirrrrty. I guess it’s all thanks to the passenger load.

    1. Plus there are only a few a day, so they fill up. The SLUT runs constantly, so it’s mostly empty.

    2. Even with all of the soot older diesel locomotives belch they are actually pretty good on CO2 per ton mile. This is thanks to the low rolling resistance of steel wheels on steel rail.

      1. And as barman said the passenger load. You fill up one big train and you’ve got quite a lot of people being moved by a single engine.

  5. Why are Metro trolleys almost as carbon-emitting as the diesels? As MP says above, City Light has to be one of the least carbon-intensive utilities in the country. I agree that the Monorail figure seems too low, plus I find it hard to consider the Monorail transit any more than that at Disney World.

    Also, another (smaller) reason for the Sounder’s numbers being so low is that the rolling resistance of steel wheels on steel rails is much better than that of rubber tires on concrete.

    1. The numbers for the trolleys are a bit surprising, especially considering they tend to have higher passenger loads than many of the diesel routes.

      I suspect the FTA numbers need to be re-run with the carbon load of Seattle City Light’s actual source mix.

      1. Anything Seattle uses to run the ETBs is electricity they can’t sell to other utilities in the region. Since we’re all sharing our regional air supply it makes more sense to use the regional average. Maybe even a wider average should be used since Washington sells surplus electricity in the summer to California (and buys it in the winter when our demand for heating is high and their demand for AC is lower).

      1. I noticed the UC Berkeley study is cited and graph included in the FTA report as Figure 4. It is possible that there is a flaw in the part of the FTA report showing CO2/passenger mile.

  6. It’s really not appropriate to use estimated C02 based on the US electrical grid. The dams will produce electricity no matter what; their overall output cannot be increased (they can shift during the day but when they lower output, they are ‘storing’ power by filling the reservoir). When you operate a streetcar and increase the power load, this causes someone, somewhere, to start up an oil-burning power plant to make up the extra. So power consumption should actually be based on marginal C02 emissions rather than overall CO2 emissions.

    In that case (aka reality), I doubt Link does well at all, and the trolley is an outright atrocity.

    1. When you operate a streetcar and increase the power load, this causes someone, somewhere, to start up an oil-burning power plant to make up the extra.

      You are assuming that we are operating at 100% utilization of the grid at all times, that proximity is irrelevant, and that all new energy sources are fossil fuel sources.

      In real reality, proximity is hugely important. Electricity distribution is phenomenally wasteful, thus potentially making a nearby dam a more attractive source of energy than a far away coal plant that’s twice as efficient.

      1. Your argument basically says that you could save carbon emissions by wasting energy in the Pacific NW. Can you possibly be serious?

        Addressing my alleged assumptions: Dams are used 100% of the time. If they are not actually generating energy, they’re closed up and building up their reservoirs, allowing them to generate more energy later. They don’t let almost any water go to waste. Also, most transportation energy is used at peak times, when it’s maximally wasteful, so this assumption of no waste is actually generous to transit. Second, in the short term, all new energy sources are nonrenewable, and almost all of them come from fossil fuel sources. Those are the only sources of energy you can activate with the flip of a switch (just burn more oil, natural gas, or consume uranium fuel). It’s true that in the long run they should be building more renewable generation sources, but are you actually arguing that we should waste as much energy as possible so as to encourage building more renewable energy sources?

        The proximity issue is indeed really important, but in fact, it is exactly why it’s so phenomenally wasteful to increase electricity use. Energy suppliers are pretty much only motivated to buy power cheaply. Not cleanly mind you (until we get a carbon tax or cap & trade in place), but in the power industry cheapness and cleanliness are highly correlated. If others were importing our power, it’s because that was the most efficient option available.

        To break it down, Increasing our use either a) causes the region to import power from elsewhere at great expense and waste, as you have said or b) causes somebody else who was buying power from us to use another source of energy. Transmission is expensive, but they were obviously importing our energy because whatever they can make themselves (almost certainly by burning coal or oil or natural gas) is even more wasteful then transmitting hydro power long distance, without even pricing in the environmental consequences of greenhouse gas emissions.

        All I was arguing is that this additional waste (either in dollars, energy, or C02 emissions) is the appropriate measure of waste in energy consumption. Sure, in theory this number could be negative (I highly doubt that is ever the case: that would mean wasting energy in one place actually reduced carbon emissions!); that doesn’t change the fact that it’s the only reasonable measure.

      2. Dams release a huge amount of water through spillways that’s not used for generation – just drive by any dam on the Columbia River in the early summer! Sometimes this is done because they don’t have room to store the water, and sometimes for reasons like fish passage. Either way, I’ve seen it with my own eyes!

      3. That’s all great in theory but it doesn’t reflect the reality of how the power grid works in the PNW nor is it how carbon emissions for comparing energy sources to one another typically calculated.

        Even a coal fired power plant powering electric transit is more efficient in terms of CO2 per passenger mile than using an on-board power source.

        Even in areas with a large amount of electrically powered transit it tends to be a very small component of regional electrical demand.

        Assuming adding electric transit requires some new generating capacity somewhere in the system for certain times of day during certain parts of the year it is most likely that the additional capacity will be added in the form of gas turbine generators (and combined cycle at that). While natural gas is somewhat expensive (though much less than it was a couple of years ago), it is by far the best of all fossil fuel sources in terms of CO2 emitted per kilowatt hour, even more so if the plant is combined cycle.

      4. For those listening, here are the reasons why “Even a coal fired power plant powering electric transit is more efficient in terms of CO2 per passenger mile than using an on-board power source”:

        1. carrying the on-board power source around is incredibly energy-heavy
        2. carrying the vehicle around is another dead waste of energy (hence trains carrying hundreds of people being better than buses carrying dozens, being better than cars carrying a handful)
        3. Fuel refining is astoundingly wasteful. (Big fossil fuel plants use less-refined fuel than cars.)
        4. Transport of fuel from well to refinery to vehicle is another giant waste of energy.
        5. Big fossil fuel plants are far more efficient than onboard engines or generators.

      5. The question demands you look at least two diff scenarios:

        * One – someone wants to go somewhere and the bus that is provided is either an electic trolley or diesel bus – and the NW electric grid is in a state where there is excess hydro capacity – in this scenario the trolley is a huge win

        * Two – again someone wants to go somewhere and the bus that is provided is either an electic trolley or diesel bus – and the NW electric grid is in a state where there is *not* excess hydro capacity – in this scenario the trolley may be a smaller win (fewer diesel particulates is a net climate win because of reflectivity concerns)

        So one question is which scenario fits the Seattle situation better?

    2. Oil-burning power plants have almost entirely gone the way of the buggy-whip – They are simply too expensive to operate except possibly in *very* extreme conditions – think of the hottest summer afternoon on record kind of conditions. Most of the peaking power plants are natural gas fired – more are coming online since they are cheap to build and, at least for now, relatively inexpensive to fuel. For most daily operations, Natural gas fired power plants are far more efficient on a CO2 basis than a diesel powered bus.

      Still, your point is well taken – people like to think that Seattle’s power is “green”, and for the most part, it is. However, during rush hour especially, a significant percentage of Seattle’s electricity is coming from fossil fuels.

      1. Coal isn’t as big of a source in the western power grid especially in the PNW. Yes the entire North American grid is interconnected but the capacity for feeding power between various segments is limited.

      2. Coal tends to be a baseload fuel so it’s in the energy mix all day and night long – PSE uses more coal than Seattle City Light so one could argue that Eastlink will be more carbon intensive. That said, even coal generated electricity used to power an electric train is more CO2 friendly than a diesel bus. Electric propulsion is more efficient as is the thermal efficiency of a coal power plant. Emissions from coal plants, while significant, are easier to control than the emissions from over 1000 diesel buses.

        Don’t believe me? Come do a pre-trip walk-around with me while I shorten my life breathing the uncontrolled Auxiliary heater exhaust from a Metro or ST Hybrid coach. They are relatively clean when warmed up but getting there generates a LOT of emissions.

        Hopefully the Orions that Metro has ordered will have emissions controls on the Auxiliary heater – Either that or an even better system of getting the coolant up to temperature so passengers don’t freeze during the winter.

      3. Great point about the efficiency of centralized power plants. Burning coal for electricity in one big plant and using the electricity to power buses and trains is way more efficient than thousands of tiny power plants in each vehicle burning gasoline. So even if City Light was burning 100% coal it would still be better to have electric transit! By the way, this is why we should be building next-generation nuclear plants–they are the only carbon-free power source that can take advantage of those efficiencies and provide baseload power (wind and solar do not work for baseload because they are intermittent).

  7. If MARC ran anything near reasonable service, they could have even better numbers. Right now, on the Frederick line where my folks live, they run one train per weekday in peak direction and take the most circuitous route imaginable. The train is frequently more than an hour off schedule, and sometimes canceled outright.

    My father (as much of a NIMBY, white-collar, McMansion-dwelling Republican as he is) has repeatedly stated that he would *love* to take public transit from central Maryland to his job in Alexandria. Unfortunately it would turn his two-hour nightmare of a traffic-ridden commute into a four-or-more hour nightmare of missed transfers between MARC, DC Metro, and VRE.

    1. The one train per day may actually be why it looks so good on paper – if that allows them to completely pack the one train and do no deadheading, their emissions per passenger mile will be low.

      1. Or perhaps because this one train on this particular route, inefficient as it is, is a pretty small part of MARC’s CO2 footprint.

  8. Appendix 1 also shows that BART has the second most efficient vehicles of all the heavy rail systems, so that must have something to do with it. Is there anyone who knows about trains who knows what makes BART trains so energy-efficient? The widely-spaced stops would seem to help, along with aerodynamic end cars, and I thought I heard that a lot of the train is made from fiberglass?

  9. What about bicycles? Probably not zero since we do exhale CO2, but we do that anyway, so what’s the marginal increase in CO2 emissions from bicycling. I’d wager it’s down toward the bottom of the list.

    1. That’s easy to calculate. Just dehydrate the extra food you’d eat because you bicycle, the mass of which is almost all carbon, weigh how much you don’t digest (don’t forget to dehydrate that, too!), subtract, account for the mass of the two oxygens, and voila!

  10. Do these calculations include the carbon footprint of line construction? For example, what will be the carbon footprint of boring the Westlake-to-Northgate tunnel?

      1. The whole point of the measurement is that it accounts for how many people each vehicle carries.

      2. Well so, it should vary according to actual ridership right?

        You can have a train with one person on it — and a SUV fully loaded with soccer kids and a mom.

        Which is cheaper per person (per mile or kilometer)?

      3. Who cares about a meaningless hypothetical? The point is that the passenger-mile numbers above, by their very definition, already reflect average SOV occupancy and actual transit ridership numbers.

      4. Average occupancy?

        They have figures across all trains? Of all efficiency classes?

        They and know the occupancy of each vehicle? So for example, they are averaging in Metro North from NYC to Connecticut and LINK light rail and they have all the ridership for each train? And how many people are in each SUV per mile?

        You’re really sure they have all that data?

        Can I see it?

      5. You have to be kidding me. How can you not understand this? Yes, I am really, really, sure they have all that data. Tell me how else on earth you think they can break down carbon footprint by transit service?

        Can see you see it? Yes you can see it. The study is linked to in like the fifth word of Martin’s post. Have at it.

      6. Transit agencies go to a great deal of trouble to figure out how many people are riding each train and bus (ticket counts, turnstile counts, farebox counts, motion sensors, people going out and physically counting people in stations). And the federal government does a lot of survey work to figure out how many people are in each car or truck. The gory details are available for those who look for them.

  11. As has been mentioned by everyone, I’d imagine the Seattle Streetcar numbers are so high because of
    a) very low initial ridership, which should increase as the network expands and the neighborhood grows
    b) the study doesn’t use the fuel mix of City Light, but rather of the wider region, probably averaged with PSE, Tacoma Power, and Snohomish PUD. City Light was approaching carbon-neutrality in ’08.

    That second one probably skews the Metro ETB ranking as well. Although it can’t skew it that much, the trolleys still have a sizable carbon footprint from maintenance. Replacement parts and fluids (just new tires alone is huge), not to mention all the diesel support vehicles (like the supervisor trucks) that they share with regular diesel coaches.

    1. The electrical impact numbers used an even wider area. It was the same in Oregon and Utah. Tri-Met probably also uses a large proportion of hydro power, but UTA probably uses more coal-based power.

  12. A fairer comparison would be the transit mode’s capacity, not its actual ridership on low-ridership routes. I believe planners use 75% as the ideal target for average capacity. That allows enough spare capacity with normal fluctuations to accommodate 30 preschoolers all going on a field trip together or 20 college students who all suddenly decide to go to the same show.

    The proper response to low-ridership routes is to decrease the number of buses, or adjust the routes/schedules, not to say that the mode has a low mileage (and presumably should be scrapped). Otherwise you get such ridiculous assertions as Link getting worse mileage than ST Express, even though trains take less energy than buses.

    Also, transit provides a public benefit even if it’s not full. The fact that the bus/train runs every 15 minutes means people are more likely to ride it when they need to go somewhere. This is not exactly related to mileage, but it is a factor in what each mode is worth.

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