In December, Alex Steffen wrote a provocative article at Worldchanging proposing that Seattle aim to become North America's first carbon-neutral city. I'm not an expert on carbon-neutrality as a whole, but I can certainly comment on the transport dimensions of it. Here are some reasons to bet on Seattle, in particular, as a place that might get closer to carbon-neutrality in transportation than most other North American cities. Ultimately, all of these are about geography.
Sustainable Power Supply
Seattle runs on hydropower. Dams are destructive to natural landscapes but once you've built them and accepted the resulting ecosystem changes, they're a sustainable power source. Electric trolleybuses are a good sign of a city's confidence that electric power would always be cheap and abundant. You'll tend to find them in hydropower-driven cities, such as San Francisco, Seattle, and Vancouver.
Density and Mixed Use
Density drives transit demand, but even more importantly it drives walking, which is the only transport mode that requires no inputs from emissions-compromised sources.
A Hard Edge = A Clear Political Identity
If you're going to do something that works best in the dense pre-car urban fabric, you need both a name for that area and a political unit that can focus on it. The City of Seattle is close to being such a unit. Seattle is bounded by major bodies of water on the east and west sides. Only to the north and south do the city and its suburbs flow together, raising some uncertainty about where one ends and the other begins. Among major North American cities only a few (San Francisco, Vancouver, and arguably New York City) have a better alignment of natural and political geography for this purpose.
At the opposite extreme, the City of Los Angeles is a bizarre shape that includes a great deal of postwar suburbia and omits a great deal of older urban fabric closer in. I often want to talk about a "core" part of Los Angeles that is high-density and urban in character, but there is no word for this area, and thus no political concept, a real disadvantage for sustainability thinking in that city.
If you want a real focus for sustainable transport improvements, however, look for chokepoints.
A chokepoint is anywhere in the transport network where many different trip paths have to go through the same point to get past a geographic barrier. Bridges and tunnels are chokepoints. So are mountain passes. Wherever a steep hill is right next to a body of water, the little ledge in between them is a chokepoint, as it often only has room for one road, or a road plus a single track of rail.
No North American city has more chokepoints than Seattle. The city itself consists of three peninsulas with narrow water barriers between them. Further barriers are created by steep hills in most parts of the city. Nowhere in Seattle can you travel in a straight line for more than a few miles without going into the water or over a cliff.
Seattle's geographical isolation from its suburbs, of course, means it is also surrounded by chokepoints. There are only two bridges across Lake Washington to the east, and to take your car across Puget Sound on the west you have to use a car ferry, which means your trip will be no faster or more frequent than that of a transit passenger.
Transit planning is frustrating in such a place, but road planning is even more so. Ultimately, Seattle's chokepoints have the effect of reducing much of the complex problem of mode share to a critical decision about a strategic spot. If you give transit an advantage through a chokepoint, you've given it a big advantage over a large area.
For example, here's a Google Earth shot of Seattle's Queen Anne Hill. Downtown is on the south edge of the image. The gridded area at the center of the image is the hill itself. Many of these streets are steep, and only a few of them connect to surrounding areas, so these limited hill-climbing opportunities are chokepoints for access to the hill. More importantly, the hill generates chokepoints all around it. Southwest and northeast of the hill are narrow "ledge" spaces between the hill and bodies of water. These ledges are chokepoints in themselves, and they also lead to more chokepoints further north: bridges over the Ship Canal. Since Queen Anne Hill is adjacent to downtown on the northwest, the chokepoints around it are a dominant transport reality for the whole northwest quadrant of the city.
The high cost of transport capacity through Seattle's chokepoints makes it relatively easy to imagine congestion pricing. (Correcting the price signals that currently favor cars would be a crucial step toward carbon-neutrality in any city.) Americans tolerate toll bridges, in part, because bridges are obviously expensive to build and maintain. You can't go far in Seattle without crossing a bridge, so there are many opportunities to expand on the existing understanding about toll bridges to create a broadly acceptable congestion pricing regime. I'm not saying this would be easy, but the geography certainly makes it easier.
What Seattle doesn't have is a lot of transit infrastructure. Its first rail rapid transit line opened just last year, though the downtown subway that the line uses is almost 20 years old. Other than this, its speed and reliability infrastructure (as opposed to the power supply infrastructure of trolleybuses) consists of bus lanes.
Seattle is used to feeling inferior on this score because Portland is just down the road, and Portland has a huge light rail network extending three directions from downtown, in addition to its much-imitated and expanding streetcar line.
Yet bus-dependent Seattle has a higher transit mode share to downtown (transit trips as a percentage of all trips) than rail-oriented Portland does.
If you think that rail transit infrastructure, all by itself, will transform your city, read that sentence again.
The lesson of Seattle is that successful transit infrastructure responds to demand, and what drives transit demand is high overall travel demand plus serious barriers to driving. In Seattle, a lot of the barriers to driving take the form of hassle and delay, due to limited capacity through chokepoints. Congestion pricing would replace the hassle and delay with a monetary cost. But one way or other, you'll pay to drive into the core of Seattle, because there isn't enough space for everyone to do it easily. Driving into downtown Portland, especially from the east where most of the population is, is easy by comparison. (Downtown Portland has so many bridges over the river that none of them are especially onerous chokepoints.)
Seattle's advantage, in short, is a natural scarcity of transport routes, which is the same as an abundance of chokepoints. Because of this geography, even in the era when we were building roads everywhere, it just wasn't possible to build an oversupply of roads connecting the various parts of Seattle. So transit's advantage remains.
Effective transit infrastructure aims for the chokepoints, and seeks an advantage there. This is part of why various forms of Bus Rapid Transit have particular potential in Seattle: if you give transit an advantage through the chokepoint, you can achieve a lot of mode shift. The bus services across Lake Washington (between Seattle and its eastern suburbs) on I-90 do well because they have preferential access through a major chokepoint. East of the lake, they spread out to serve many suburbs directly, something buses do easily and rail does only with a required transfer.
Obviously, none of this is an argument against rail rapid transit, in Seattle or elsewhere. Rail can provide higher capacity per unit of operating cost, and where the alternative is non-electric buses it has an obvious emissions advantage. But it does mean that in Seattle, rail is about increasing the efficiency with which we carry people who already have a motive to use transit, and also building the capacity that will be needed if and when congestion pricing becomes realistic. (London's abundant transit, remember, was an important part of the case for its congestion pricing scheme.) That means that rail and bus improvements both need to aim for the chokepoints, and win focused battles for capacity there.
This topic continues here.