The Downtown Seattle Transit Tunnel has improved transit in Seattle more than any other project. Long before it served trains, it served buses (and still does). Thousands of buses have gone through it, saving passengers thousands of hours in travel time. Now it is an essential part of light rail — by far the most important part. It wasn’t cheap to build, but compared to the rest of the system (such as the Beacon Hill tunnel, the surface rail on Rainier Valley or the elevated rail to the airport) it is a tremendous value.
At a point in the not too distant future, the tunnel formerly known as a “bus tunnel” will only serve light rail. This is a good thing, but it means that some buses, especially those from the south, will be forced to the surface through downtown or rerouted elsewhere. At the same time, we are in the midst of planning for high speed transit from Ballard to downtown and West Seattle to downtown. We should build a new tunnel to address all of these issues.
I propose a new transit tunnel through downtown that will support both buses and light rail. From the southern end, it would start (and connect seamlessly) with the SoDo busway. In the middle, it would parallel the existing tunnel at least in part, allowing for easy transfers along the route. The northern route is trickier. The big question is whether to pay the extra money to include Queen Anne, and if so, which parts of Queen Anne. Corridor A includes stops on upper and lower Queen Anne. This wouldn’t be cheap, but it would certainly be popular. Corridor B only include a lower Queen Anne stop, and saves money in the process. Arguably the best value would be a modified Corridor C. This would be significantly cheaper, especially if much of the tunneling work could be done as cut-and-cover (just as the original tunnel was built as a mix of cut-and-cover and boring). I really don’t have a strong opinion on which northern route is best, as the costs are so sketchy. In general I would say that each proposal has merit, and that each route would be a good value. It is simply a case of how much extra we want to spend for the extra ridership. This decision (the exact northern route) does not alter the basic proposal — a second, mixed use tunnel would be a great value for the city.
The Southern End
Bus riders who live or travel south of downtown Seattle would benefit greatly by this tunnel. The SoDo busway is a great asset for buses. It connects freeways in the area with downtown (through the existing tunnel). With relatively inexpensive changes, the buses could connect from the south to downtown in a fast, exclusive way. WSDOT is currently improving the HOV lanes and has plans for more. Fairly soon, there will be HOV lanes continuously from Tacoma to Seattle. The state has also proposed adding a ramp to better connect I-5 to the SoDo busway (they don’t have a project website, but it is the second proposal listed here). This would enable a rider to go from Tacoma to downtown Seattle in an exclusive lane the entire way. Similar changes could be done for West Seattle. Parts of the West Seattle freeway are already HOV only, but more could be done on the freeway itself, as well as to connect the freeway to the busway. This isn’t cheap, but it is a lot less expensive than new light rail because much of the work has been done, and buses can travel a more steep grade than trains. For a lot less than the cost of the cheapest light rail line to West Seattle (serving only one station) you could add miles of exclusive lanes and ramps. With the money left over, you could fund countless improvements to the buses in the neighborhoods (exclusive lanes, traffic light priority, offsite boarding, etc.).
Speed Now and More Capacity Later
Unlike the existing tunnel, this new tunnel could be designed for off board payment from the very beginning. It would also be designed to handle buses and trains the day it opened. Like the transit tunnel, it could accommodate future rail expansion. If West Seattle ever gets populated enough to justify the extra capacity and cost of light rail, then the tunnel could handle it.
One alternative is to build light rail from West Seattle to this tunnel immediately. I could spend a lot of time explaining why I think this is a bad value, but consider, just for a second, how exactly that would be better for folks in West Seattle. The population in West Seattle, as in much of Seattle, is spread out. This means that you wouldn’t get very high ridership unless you funnel people (via buses) to the station. There is nothing wrong with that — it plays a large part in why I think this route makes so much sense. But in the case of West Seattle, it makes a lot less sense. Buses in the area can, in many cases, get to the freeway faster than they can get to a subway station in West Seattle (assuming there is only one subway line). This means that there would not only be a transfer penalty for most riders, but little to no time savings while riding. The transfer penalty could be substantial — Sound Transit expects headways on the West Seattle line of ten minutes (and that is during rush hour). It is important to remember that buses and light rail travel at about the same speed. The time savings come from grade separation, not vehicle capability. For this corridor, it is a lot cheaper to build that grade separation for buses, not rail. Rail is still better from a capacity standpoint, but at this point, it simply isn’t needed for this area.
Buses from Tacoma could simply use one of the other stations (such as the one in Tukwila). But that would cost riders a lot of time. Unfortunately, unlike the rest of the system, the train moves very slowly, and very infrequently between Tukwila and Seattle. Even transferring riders from Renton to a station at Rainier Beach would cost riders a substantial amount of time.
Another alternative is to use the SoDo station as the endpoint for buses. To do that, you would need to build a bus station there to allow buses to turn around. For this type of system to work, you would need very frequent rail service (think Toronto, not Washington D. C.). Unfortunately, I don’t think this will ever happen. Trains from the south will never be able to travel very frequently through the Rainier Valley. Sound Transit could add a turnback station in the SoDo area and send additional trains there, but there are significant limitations with that approach. Headways are limited in our central core, and some of those trains will branch off to the east side. Simply put, I don’t think we will be able to have the kind of frequency from SoDo to make such a transfer painless. The transfer would not be as bad as the one in West Seattle, but it wouldn’t be good, either.
Another approach would be to build a short tunnel from the southern entrance of the existing tunnel to the International District station. That would allow someone to make one transfer to any other part of the system. Furthermore, this puts it much closer to the heart of downtown. Even if SoDo becomes more popular, I doubt it will never be as popular as the area surrounding the International District. If not for the work being considered for Ballard, this would make a lot of sense.
As Bruce Nourish mentioned, the most important part of the Ballard to downtown line is from Mercer to downtown. The rest of the route can be done on the surface, with little time penalty (less than a minute). But through downtown, you need a tunnel. It makes sense to run this tunnel as far south as the SoDo busway, and have the southern end serve buses not only from West Seattle, but from Tacoma, Renton and other areas.