HIGHLIGHTS FROM THE APRIL 2006 ISSUE | |||
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The need for a light rail system is particularly acute in Seattle simply because of the way that geography has determined the city's development. Downtown Seattle is shaped like an hourglass, hemmed in by Puget Sound to the west and Lake Washington to the east, with residential areas extending far to the north and south, and east of the lake. High-density development and the University of Washington campus just north of downtown have contributed to heavy transportation demand in a constrained north-south corridor.
In 1993, the Oregon state legislature authorized formation of a regional transit plan. The Central Puget Sound Regional Transit Authority (Sound Transit) was created, encompassing the urbanized areas of Snohomish, King, and Pierce counties-an area that stretches almost 100 miles north and south from Everett to Tacoma. The $3.9 billion, 10-year Sound Move plan, approved in 1996, included development of commuter rail from Lakewood all the way north to Everett; LRT from a point south of Seattle-Tacoma International Airport to Northgate, as well as a short LRT line in downtown Tacoma; and a regional express bus system. With the 1996 plan nearing completion, the regional system is now moving ahead with Sound Transit 2, a new long-range plan.
Central Link LRT
The $2.4 billion Central Link Light Rail will be Sound Transit's single-largest project. An initial 13.9- mile, 12-station segment now under way will extend from the Westlake station in downtown Seattle to the Tukwila International Blvd./Southcenter Blvd. station north of the SeaTac Airport. The alignment will include seven miles at grade, 4.4 miles in elevated structures, and 2.5 miles in tunnel, including Downtown Seattle Transit Tunnel and Beacon Hill tunnel. Work begins this year for a 1.7- mile extension from Tukwila to SeaTac Airport. Construction is now more than 40% complete.
Central Link's design largely follows typical modern LRT practice. But in a deviation from normal practice-the first in North American light rail-overhead power will operate at 1,500 volts d.c. instead of the usual 750 volts d.c. This will enable Sound Transit to reduce the number of power supply installations and the size of overhead contact wires. Propulsion will be with a.c.-drive IGBT traction motors. The 35 LRVs from a joint venture of Kinkisharyo International LLC and Mitsui & Co. (USA), Inc., will be a 70% low-floor, double-articulated car capable of operation in trains of up to four cars in length. Each car will seat 74 passengers, with a total capacity of 200.
Seattle's Downtown Tunnel trolleybus service was converted to surface operation in September 2005 during a two-year construction period while the tunnel is retrofitted for rail. Trolleybuses will return to Tunnel operation in late 2007, followed by LRV testing. Track construction and a Link operations and maintenance facility will be completed in time to begin test operation, as deliveries of the first LRVs begin in fall 2006.
The most difficult Link construction will be the 0.9-mile Beacon Hill Tunnel. The shafts of the station, 165 feet below the surface, were excavated with a slurry wall method, with cement grouting used in areas of poor soil. A concourse level connects the separate tunnels for platforms and tracks. A 642-ton tunnel boring machine (TBM) named the �Emerald Mole� will use a rotating head to excavate the 21-foot diameter tunnel, which will be followed by installation of pre-cast concrete segments.
Map: Sound Transit; Inset: William D. Middleton
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