Last week, Sound Transit recalculated the cost of bus rapid transit to the Eastside by $2 billion — downward. Suddenly, the case for buses looked a lot better.

That case begins with the obvious: Buses can go wherever rubber tires take them. A bus system can serve every large neighborhood. It is flexible. It can change routes. It can be added to in small pieces. It exists now, and it works.

The Seattle area carries a higher proportion of people on the bus than does Portland on bus and light rail.

In contrast, light rail starts from scratch — from mile zero. It costs so much money that we're never going to have very many miles of it. And it soaks up billions that could be used for bus lanes, bus stations, signals, etc., that could serve a much wider population.

For three and a half years, this page has argued that a modern bus system, called bus rapid transit, is the way to go. We still believe so, though the decision is made more difficult with one light-rail line under construction.

Each step wedges open the door to the next. The southern line, which is being built down the Rainier Valley, will lay claim to the downtown bus tunnel. But it cannot justify exclusive use of the tunnel without a northern line, and it cannot get efficient use without a line to feed more people into the tunnel's southern end. This is one reason the proposed Eastside line uses Interstate 90.

That proposal is one of six general configurations Sound Transit is showing the public. Four of them make use of I-90 and not Highway 520, even though Highway 520 is aimed toward a larger concentration of people.

Several of the six make use of the rail right of way on the Eastside now used by the Spirit of Washington dinner train — an intriguing idea, but one bound to stir neighborhood opposition.

Estimates of capital costs range from $2.3 billion to $6.8 billion, with bus options toward the bottom and rail toward the top, and with operating costs favoring buses.

It is early yet. Sound Transit does not have the tax authority for any of these six plans, or to get to Northgate. The agency will be holding hearings, with a public vote coming perhaps a year and a half from now. There is ample time for the public to consider these visions, and to respond.