As the three-county area served by Sound Transit prepares for the November vote on the future of the system, as part of the Regional Transportation Investment District (RTID), the benefits of light rail (or lack thereof) have come under close scrutiny. The plan, which calls for $11.5 billion in investment in light rail, is certainly expensive. The costs, however, are balanced by significant benefits in terms of transit capacity and environmental impacts. Light rail does, to be sure, require a great deal of capital investment due to the need to build fixed-line tracks, usually on separate rights-of-way. In Seattle, the situation is complicated by the hilly nature of the landscape; the tunnel being bored under Beacon Hill is far more expensive than the normal cost of light rail. (An additional tunnel under Capitol Hill will be built regardless of the outcome of the November election). Still, next to the cost of a replacement for the Evergreen Point Bridge for Highway 520, light rail looks downright cheap. There is, moreover, a payoff: significant ridership gains. The advantage of light rail over other transit modes is that it attracts new ridership to a far greater degree. There are a variety of reasons for this, including the oft-noted phenomenon known as "rail bias." Despite the name, there is nothing irrational about preferring the advantages of rail over the discomfort and inconvenience of buses. Sound Transit's lines will greatly increase transit capacity along the corridors they serve. Because most of the line will have its own right of way, it will to a large degree be able to avoid congestion. During peak times, trains will run every few minutes, providing regular, dependable, and fast service. As the region grows and increases in density, train frequency can be increased to meet demand without affecting travel times. This is the advantage of light rail: It can move large numbers of people, quickly and efficiently, over a set corridor. Sound Transit's projections estimate that, when completed, the system will see 350,000 daily rides, more than King County Metro's bus service currently provides. Opponents of light rail often rally around the alternative of bus rapid transit (BRT), which they see as a cheaper alternative. Bus rapid transit, unfortunately, is a chimera. To be viable, it too requires separate rights of way and thus large capital costs; these fixed routes are no more flexible than light-rail lines, even if the vehicles, in theory, are. Moreover, it does not create much new ridership but rather cannibalizes the riders of existing bus routes. Vancouver runs three bus-rapid-transit routes. They're also planning to get out of the BRT business, replacing the existing routes with light-rail lines. The reason? Light rail has more capacity for expansion of service and attracts more ridership. Ottawa, meanwhile, built a BRT route that ended up being roughly as expensive as a light-rail line and proved to be a massive headache, because buses were constantly getting snarled at stations. All in all, bus rapid transit is exactly what the detractors of light rail claim to want to avoid: a massive waste of public money with little benefit. Despite claims by its detractors, Sound Transit will also have a positive environmental impact. Last week, Crosscut published a piece by Emory Bundy criticizing Sound Transit and arguing that the construction of the light-rail line would be environmentally destructive. The argument rested on two premises: first, that construction of tunnels for the system would unleash enormous amounts of greenhouse gases, and second, that light rail is not significantly more energy efficient than automobiles. The first premise has some merit, the second is categorically false. Let's start with the second claim, that rail isn't that much more efficient than cars. Bundy relies on U.S. Department of Energy statistics that are deeply flawed. They are based on ridership statistics for trains and buses that are far lower than is appropriate for a major metropolitan area: 21.7 passengers per light rail vehicle, 8.7 passengers per bus. They also vastly underrate the fuel efficiency of rail vehicles and buses alike; for alternative measures, see this Wikipedia article or this detailed look at specific vehicles. The general pattern is clear: On a per-passenger basis, both trains and buses are several times more fuel efficient than automobiles, with trains having a significant advantage over buses. A real-world example: Vancouver's light rail line achieves an average fuel efficiency equivalent to 346 passenger miles per gallon, while BC Transit buses achieve 105 passenger miles per gallon. During peak travel times or with increases in ridership, transit's efficiency advantage becomes even more pronounced. Tunneling does, as Bundy claims, require large expenditures of greenhouse gases; his metric is 1.3 million tons of CO2 (the Federal Transit Administration endorsed an estimate of 640,000 tons). And, as Bundy argues, it will take some time for the rail service to make up this cost. While it would be unwise to glibly ignore the costs of construction, it is reasonable to allow for a transit system to achieve benefits over time. Moreover, the tunnels Bundy cites have already been approved and are not part of the RTID proposal. Any other major increase in transportation capacity, be it bus rapid transit or new highways, would similarly incur a large expenditure of CO2 without the future benefit of reduced emissions. Bundy advocates two other options: bikes and vanpools. King County Metro already runs the largest public vanpool program in the United States. Moreover, Seattle is at least in theory beginning to implement a significant plan to increase the viability of bicycling as a mode of transportation, though it remains to be seen whether the city has the political will to take the necessary steps. The overall picture, though, is that Seattle and its neighbors are building a comprehensive transit system that provides a variety of attractive options to commuters. Expanding Sound Transit is an important part of completing that system.