The typical Seattle-area bus has 42 seats. One of the big, articulated buses has as many as 64 seats. But on a commute the other day, I counted at least 92 passengers in my bus, including folks who were standing in the aisles. There were so many folks on the bus that the driver had to leave a few would-be riders at the bus stop.
And then there’s rail. Seattle’s soon-to-be-opened Link Light Rail will have 74 seats per car. But including standing passengers, each car can hold as many as 200 passengers. If transit ridership stays high, and commuters take to rail as much as some people hope, I imagine that many of the rail cars will be close to full during peak hours.
I mention all this because of the ongoing debate over the climate impact of various forms of 
transit. In particular, I’ve gotten some very reasonable pushback on the chart to the right, which we published last year. The chart compares the climate impacts of different transportation modes: the blue lines represent CO2 emissions, measured per passenger mile traveled.
But as you may notice, I don’t estimate the impacts of buses or trains that are full to capacity. That may be an oversight, since quite a few buses are over-full at this point! If I were to bump the ridership figures up to actual peak levels that we’re experiencing now, the climate impacts of rush-hour transit would look even better.
Now, new research out of UC Berkeley confirms these findings: when a transit vehicle is reasonably full, it’s a fantastic deal for the climate. And that’s true even when you consider the entire “life cycle” impacts of travel—including the CO2 released from manufacturing vehicles, and building roads and rail lines.
The Berkeley Institute for Transportation Studies recently took a look at comprehensive life-cycle emissions from various forms of transportation, focusing on the Bay Area. Take a look:
As you can see, a well-utilized transit system—a peak bus, or a BART train—can cut CO2 emissions by well over two-thirds, compared with driving.
The ITS has done a real service here. By including the impacts of fuel production, infrastructure, and vehicle manufacture, they’ve made the comparisons of different travel modes much clearer. So we can see, for example, that building a rail line (the red segments) has quite significant greenhouse impacts. Still, the overall emissions of trains are far better than for cars.
To me, the most interesting comparison here is the buses. At rush hour, buses do great! Off-Peak, buses do lousy! The only real difference is the number of seats that are filled. A near-empty bus trundling along at 3 to 4 miles per gallon is no great deal for the climate.
We could probably do similar peak-vs-off-peak comparisons for cars and trains as well. During rush hour, cars do worse than they do at other times: people commuting to work are particularly likely to drive alone. But a rush-hour BART train is likely do even better than the lines above indicate, since that’s when the trains are fullest.
I love charts like these. But unfortunately, we have to interpret them with care; it’s easy to misunderstand their messages. To me, the clearest lesson in all of this is that the best way to reduce the impact of travel is to fill seats. Train, bus, vanpool, car—as long as there aren’t too many empty seats, they’re all fairly comparable. If the seats are empty, they’re bad news. So the bus vs. rail debate is mostly a distraction. Neither mode is inherently better; full, they’re pretty close; and as long as they attract enough riders, both are much better than driving.
Bus photo courtesy of Flickr user dkjd under a Creative Commons license.
Matt the Engineer
(sorry, Seattle-area specific comment ahead)The second graph shows one reason the 20/40/40 rule is so frustrating. In King County we have a rule that 20% of new bus service goes to Seattle, 40% goes to the east side, and 40% goes south. The problem is that these east and south routes have much lower ridership numbers than anything in the city (which generally have buses filled to the gills), and are more or less empty except during commute hours. I understand the intent – to build new ridership over a longer distance. But it would be nice if we maybe had smaller, more efficient buses for these routes during off-peak hours.
Clark Williams-Derry
Amen to that, Matt.
deb eddy
Agreed – bus v. rail is a distraction if all we’re talking about is unit CO2. HOWEVER, other variables bring into play (1) cost, (2) where/how you gain/attract ridership (new v. existing, i.e., actually getting people out of their cars as opposed to merely switching them from a bus to a train) and (3) whether/how there is opportunity for redevelopment (especially housing) along the rail corridor.Matt is right that the 20/40/40 is maddening. But before we double the number of buses in the barn … maybe we should reconsider routing methodology?
ecwasserman
If you the chart the best public investment would be to have consumers purchase a Prius. They function particularly off-peak much better than mass transit. While transit would be a good investment for peak hours, that only represents 20% of all trips. Many transit and bicycle trips involve the use of a car.Public financing for the purchase of technically advanced cars looks like a better public investment than most rail projects.
Clark Williams-Derry
Maybe so, ECWassserman. Of course, there are other things to consider too—the public costs of parking a Prius, accident risks, etc. Climate isn’t (and shouldn’t be) the only consideration in transportation investments. That said, if a careful evaluation shows that Prius tax breaks are the best overall investment, I’d be for it. (My guess is that transportation demand management—low-cost programs that help & encourage people to take fewer car trips—would turn up close to the top of most cost-benefit lists.)
8string
Right you are about the empty buses, which have been a pet peeve of mine since the 80s. All you have to do is stand on an overpass at Montlake, between 9 and 10 and count the empty buses heading back to their East Base any weekday. Probably, from your charts, I can extrapolate that we might be reversing the good we are doing by sending them back to their base empty. Not to mention that they clog up the freeway at a relatively peak hour for east side trips. That’s while lots of folks wait for an less than full bus heading to the east side. And yet we want to widen more freeways… it all seems like we continue to strive for some perfect world in 30 years while some basic solutions seem to sit right in front of our eyes.
Jeffrey Belt
I was going to react to the statement that a car, any car, could be the best transportation investment, CO2-wise, until I realized the non-motorized modes are not included in the chart. I’m guessing biking has the lowest CO2 emissions, but I expect walking to be very low as well.Deb mentions that the type of transit affects development. I wonder if we have to saturate our cities with a dense network, so that over the years, they’re rebuilt filled in, and walking becomes possible again. This seems like an expensive way to get to the cheapest mode of travel yet invented. 🙂
deb eddy
We have a statutory mandate to reduce vehicle miles traveled. Good reasons, don’t need repeating here. Tele-commuting is only going to cover so much of the VMT reduction. Yes, over time, that rebuilding/infill development SHOULD make it possible for more people to use the cheapest mode of travel yet invented for many daily needs/tasks … we are talking about the amazing bipedalism of humans, aren’t we? :-))
Matt Leber
Metro tries to minimize dead-heading where they can. For example, I have driven a 229 to Seattle, followed by a 217 to Issaquah, followed by a 212 back to Seattle, and then return to East Base picking up any bicyclists wanting to cross 520.They also use “storage trippers” out of North base where some of their coaches are stored at downtown bases during the day while the drivers are loaded up onto a coach headed back to North Base (661 if you’ve ever seen it).We also occasionally carpool when doing road reliefs (drivers running around in cars), but that can be difficult to coordinate.I suspect more could be done here, but anything that makes the system more complicated can affect service – something Metro works hard to avoid.
Kevin Matthews
I’m trying to track the operational versus lifecycle costs versus vehicle utilization dimensions back through the study itself, and what I’m seeing looks like a whole lot of squishiness. Looking at “Environmental Life-cycle Assessment of Passenger Transportation…” Chester, Horvath, at:http://www.sustainable-transportation.com/one wonders, among many other questions, why Table 23 shows the diesel bus with 16 vehicle miles per gallon?Looking at the study itself, building up one debatable assumption after another, I’m seeing a lot of precision, but any real accuracy is harder to determine. It’s important stuff – which deserves to be vetted, reviewed, and adjusted in detail, before we draw much from it in the way of conclusions.
Clark Williams-Derry
That’s helpful, Kevin, and very important work. If you come to any conclusions, please let us know!
Barry
Clark, I totally agree that *occupancy* is an essential part of reducing travel emissions.But neither your chart nor the BITS chart allow readers to easily make educated decisions based on occupancy. I used the data you had for your chart to build a chart that does show emissions by occupancy for many modes of transport. This was published in the BC environmental magazine, Watershed Sentinel, and has been very popular. Readers can view this online at http://www.saxifrages.org/eco/show7a . I’d be happy to supply spreadsheet and sources if you want to review and publish on Sightline as well.When you look at occupancy it is very clear that FULL high-mileage cars and buses are by far the best option. Perhaps there are some trains systems that are equal to these but i’ve not seen data on them.What is also clear is that air travel is almost always the worst possible choice…often 10 or 20 times worse per passenger mile than high-occupancy road choices. If you want to give people info on what they should choose in their own lives you need a chart that compares modes AND occupancy levels like my chart does. Remember, the one thing most people CAN control is occupancy-level of a car. And if they fill a fuel-efficient one they will almost certainly be making a better choice than train or flying.To try to get a feel for BITS chart, i looked at BITS paper and found the following occupancy levels used:* sedan: 1.5 people* bus off-peak: 5 people * bus average: 10.5* bus peak: 40* trains: “average” (unable to find specifics)* airplanes: “average” (found a number but not as percentage of max)This BITS chart once again shows a huge pro-flying bias typical of those that love to fly. Why doesn’t it show “off-peak” flying and “peak” flying? Where are the private jets that are the fastest growing source of emissions? Where is the first-class vs. coach discussion? All of these are huge emission sources that are ignored.Furthermore, there is no way the per-passenger-mile CO2e tailpipe emissions from an average airliner is *less* than CO2e for a 1.5 person-occupancy average sedan. But that is what BITS chart says. This contradicts every study i’ve seen, and i’ve seen lots and lots. The only way to get this number is to ignore the additional ghg-forcing of airplane exhaust as described in IPCC Special Report on Aviation. I looked in BITS paper and i could find no mention of how they determine CO2e for airplanes and no listing of IPCC aviation reports. So take their airplane numbers with a huge grain of wishful thinking.In the end, if you want to make the best ghg choice for your own travels you will need to dig deeper than these macro-policy charts.
Jon Morgan
I don’t understand why data like this hasn’t been used to create a slugging system/network/culture like DC has. It’s a much more flexible version of carpooling, and it’s a win-win since the solo driver gets to use HOV lanes, and someone without a car gets a faster ride home, or to their park and ride for example. The Seattle, King County, and WA DOTs ought to be working on this.
Barry
Clark, I realized that what really bugs me about these kinds of charts is that they are snapshots looking backwards. They record our average-vehicle choices and our average-occupancy choices in the past.But everyone knows these average choices are unsustainable. Making choices based on these will lead to more of the same. Instead, we need to understand what the best choices are going forward, in both short term and long term. This is true for both personal and policy decisions. To be useful in personal and policy planning, charts like those above need to expand to show best options not just current averages. We need to put our money and energy into best options.For example, the best-case for flying (best plane, high-occupancy) is absolutely terrible compared to best-case for driving (high-mpg, high-occupancy). But you would never get that from the BITS chart. Even a full average SUV today is much better than best-case flying. Ditto for driving vs trains. The charts make trains look vastly better than driving. But driving can be as good, or even better, than trains. The BITS “Sedan” bar should be paired with another “Sedan (peak)” bar for 4 passengers. This would then be better than Green Line, Caltrains and maybe even BART. If you add a “High MPG Sedan (peak)” it might be as good or better than “Bus (peak)”. We need to leapfrog our transit choices rapidly to best-options if we want to maintain mobility through climate crisis and end of cheap oil. The information we use to make these decisions needs to make clear what these best-options are…not what is the least terrible of our past average choices.Kudos for driving home the “fill the seats” message in your writing. It would be great if the charts you post…which so many people rely on alone…also showed this essential truth.
Barry
A friend just sent me these charts that shows MAX POSSIBLE efficiency for different transport modes. This is what i’m talking about. We need to highlight what the best case scenarios are for future policy and dollars. We are not going to have the luxury to waste fuel the way we are now…so occupancy is going to change by necessity.Also the chart includes a fully occupied Telsa Roadster for a glimpse at electric car future options.http://strickland.ca/efficiency.html
John Niles
Following up on Kevin Matthews’ posting of 11/06/2008 that correctly observed a suspiciously high mpg number for diesel buses in the UC-Berkeley study: I contacted Dr. Mikhail Chester the study author who informed me that his dissertation, also posted at http://www.sustainable-transportation.com/, is the up-to-date replacement for the working paper found by Kevin, with many revised numbers. The bus fuel efficiency number behind the chart posted by Clark at the top is 4.3 mpg, found in Table 25 of Chester’s thesis. Much more believable.