Light Rail or Buses in the Downtown Seattle Transit Tunnel:
Assessment of Benefits to King County Metro
and Regional Public Transportation

  ITR Tunnel Team Report to
King County Council Transportation Committee


John Niles, Dick Nelson, and Jim MacIsaac
Integrated Transport Research, Inc.

Complete Tunnel Team report in PDF (1.5 megabytes)
Bus Rapid Transit Brochure in PDF (340 kilobytes)

 Executive Summary
(Updated, November 17, 2001)

This report was prepared by the Seattle consulting firm Integrated Transport Research, Inc. in response to an assignment made in early June 2001 by the King County Council Transportation Committee to assemble and analyze information that bears on the future use of the Downtown Seattle Transit Tunnel by Sound Transit's Link Light Rail.

The 1.3 mile Downtown Seattle Transit Tunnel (DSTT, or simply, the Tunnel) is the centerpiece of the local and regional King County Metro bus system. Across the entire County, Metro serves 100,000,000 riders per year. The Tunnel lets 25 regional express routes – producing about a quarter of the rush hour bus traffic in downtown Seattle – move buses two to three times faster than those on surface streets of the Central Business District (CBD). The Tunnel served 8,700 riders during the afternoon peak hour in 1998, with daily boardings of about 23,000.

ITR has concluded that conversion of the Tunnel to light rail is likely to make downtown Seattle street congestion in the 2010 to 2020 period much worse than the alternative of simply routing more buses through the Tunnel. Putting more peak hour buses into the Tunnel in the near term is recommended by the Link Project Review Committee, the Downtown Seattle Association, and this study. The Tunnel could support double the current peak period bus volumes: 300 per hour using the existing buses and route structure.

By examining Metro and Sound Transit planning documents, we have identified several reasons that downtown Seattle congestion would worsen with light rail running in the Tunnel:

• Some or all of Metro’s 25 current regional express Tunnel bus routes would be permanently routed onto downtown streets, with the frequency of these routes increasing over time to serve more customers.

• Existing local Metro bus service to downtown Seattle would likely see only a small reduction despite impressions that light rail will be a substitute service that eliminates many buses. If customer demand for public transport from locations not served by Link light rail is to be met in the future, local Metro bus service to downtown would have to be expanded.

• Expansion would also occur with non-Metro regional express bus services to downtown Seattle that could not sensibly be rerouted to be intercepted at light rail stations outside of the CBD.

Joint bus and rail operations following reopening of the Tunnel would not allow safe underground passage of enough Tunnel buses to compensate for the previous three sources of bus growth on the streets of downtown.

Existing planning studies of light rail from Northgate to South 200th reveal that rail in the Tunnel would cause approximately 680 buses to travel in the year 2020 afternoon peak hour on downtown streets, 48% higher than today’s level of 460 buses. The number of  buses in downtown in 2020 would be even higher if the Link light rail system were truncated short of Northgate or S 200th. Noteworthy is that this number of buses on the downtown streets would be higher than the number achievable with the DSTT remaining an all-bus facility.

Joint bus-rail operation in the Tunnel adds additional cost and risk with no substantial benefits. The risks arise primarily from the unprecedented prospect of intermixing buses weighing 66,000 pounds with 600,000 pound trains in a confined space with four or five station stops. Safety in peak periods will have to be achieved by limiting the frequency of buses and trains, thus setting a limit on capacity.

Ramping up the number of buses running through the Tunnel in the afternoon peak hour without interference from trains offers more and better regional transit service to downtown Seattle at lower street congestion levels than the alternative of putting Link light rail in the Tunnel.

Our findings contradict Sound Transit’s 1994 conclusions that light rail is necessary to supplement bus service in order to provide sufficient future transit service to downtown Seattle without congesting streets with a growing number of buses. This contradiction springs from the fact that the system level alternatives analysis contained in the 1993 Joint Regional Planning Committee Final Environmental Impact Statement for regional transit did not provide officials with an unbiased, realistic comparison between feasible bus/rail and all-bus/transitway alternatives that provide comparable service levels.

The "fatal flaws" in the 1993 bus/transitway option (specifically, buses facing congestion in the Seattle CBD, in the University District, and across the Ship Canal) could and should now be revisited to see if they can be corrected using Sound Transit's funding sources applied to a stronger bus plan designed by Bus Rapid Transit specialists.

Additional advantages of Bus Rapid Transit are described in a seven page brochure issued December, 2001 and available in PDF.

Revisiting an updated, expanded express bus plan is an important option given the fact that an approved, feasible, and funded light rail plan does not yet exist today, five years into the ten-year Sound Move Plan passed in 1996. Federal approval of the emerging light rail starter line will not come until 2002. Sound Transit officials have admitted that the long-run vision for a light rail system may have to be truncated at its Phase One terminus points Fortunately, the Federal Transit Administration is placing new emphasis on Bus Rapid Transit (BRT) as a lower-cost substitute for light rail. This provides further incentive to examine the option of implementing an updated BRT system as a total replacement for Link light rail.

At the same time, the forecast that Link light rail (if built) would carry mostly Seattle riders between points within Seattle underscores the intra-Seattle transit opportunities that could be filled by monorail, in-city BRT corridors, or other options that are under study now in the Seattle Intermediate Capacity Transit project and by the Elevated Transportation Company.

Summary of Findings

These findings are detailed in the full report:

Finding 1: Operating Link light rail in the Tunnel would mean that the regional inter-city express bus service for which the Tunnel was originally built would be replaced with intra-Seattle light rail service.

Finding 2: If the Tunnel were converted to rail use either jointly with buses or exclusively, express bus service quality would decline for suburban riders.

Finding 3: Joint bus-rail operation in the Tunnel introduces additional costs and operational uncertainties to Metro over simply converting the Tunnel to exclusive rail.

Finding 4: Joint bus-rail operation in the Tunnel would introduce additional safety risks over simply converting the Tunnel to exclusive rail.

Finding 5: Converting the Tunnel to partial or full light rail use would degrade transit capacity and increase traffic congestion on downtown streets both during and after the two-year period of conversion.

Finding 6: Seattle downtown bus volumes and congestion could be reduced by expanding the volume of buses in the Tunnel above present levels.

Finding 7: New bus propulsion technology, combined with a low-floor design, would permit faster loading times and cause fewer delays than the present buses used in the Tunnel, and thus would increase its effective bus capacity.

Finding 8: The passenger capacity of the Tunnel in peak hour conditions is sufficient to carry projected 2020 passenger loads with either buses or light rail trains providing service.

Finding 9: Projections of post-2020 transit ridership based on the growth of employment, commercial services, and residential population in the Seattle downtown indicate the need for planning new transit corridor capacity and demand management measures.

Finding 10: Sound Transit's north-south Link light rail line, if implemented, would offer transit performance inferior to regional express bus routes on upgraded roadways.

Finding 11: The cost-effectiveness of an all-bus alternative for regional high-capacity transit in the Puget Sound region has not yet been compared to a light rail system like the one proposed by Sound Transit.

Finding 12: The overall quality of the Puget Sound regional transit system could be maintained and improved by retaining the Tunnel for all-bus operations, increasing the numbers of regional routes using the Tunnel, integrating long- and short-haul routes, and enhancing the roadway system for congestion free bus travel.

Finding 13: The existing express bus services of Sound Transit, Metro, Community Transit, and Pierce Transit have many of the attributes of Bus Rapid Transit (BRT), and could be enhanced to bring them closer to BRT.

Finding 14: Because Bus Rapid Transit (BRT) is a new Federal transit mode emphasis, Federal and Sound Transit funds could be reprogrammed to support an extensive Puget Sound regional BRT system.


1. Authorize use of the DSTT by Sound Transit for buses only.

2. Reprogram money now budgeted for Central Link light rail to expanding Bus Rapid Transit (BRT) in the Sound Move Plan.

3. Work to implement a regional BRT plan that integrates ST Express and Metro bus services, and that maximizes the use of the DSTT.

Download the entire report updated final report (November 17, 2001) including a supplement on Tunnel Capacity from DMJM+Harris (1.5 megabyte PDF)

John Niles of Global Telematics served as project manager for the Tunnel Team. Other members were Dick Nelson, President of ITR, Inc., and Jim MacIsaac, PE, independent consulting engineer.