The service, known as Westside Express Service or WES, will operate between Beaverton and Wilsonville, using a combination of new and rebuilt trackage. This includes portions of the former Southern Pacific Tillamook Branch from Beaverton to Tigard, and the former Burlington Northern (Oregon Electric) line From Tigard to Wilsonville. These lines are currently operated by the Portland & Western Railroad.

TriMet will operate the service in partnership with the Portland & Western. The initial schedule has 16 round trips (eight each during the morning and evening rush hours). Trains will operate in both directions every 30 minutes, and will take approximately 27 minutes to run between the two endpoints.

At the north end of the route, service will begin at the Beaverton Transit Center, providing direct cross-platform connections to two MAX routes (the Gresham-Hillsboro Blue Line and the Beaverton-Portland International Airport Red Line) and 11 bus lines. To reach the transit center, construction crews laid a new stretch of single track along SW Lombard Street in downtown Beaverton from a connection with the existing rail line.

Three intermediate stops are currently under construction. These are Hall-Nimbus, off Hall Boulevard near the Washington Square shopping complex; Tigard, on SW Commercial Street at the Tigard Transit Center; and Tualatin, along SW Boones Ferry Road on the west side of the downtown area. Park-and-ride lots will be available at all stops except Beaverton Transit Center. The Tigard stop will also provide direct connections to five TriMet bus routes. The Wilsonville terminus will provide connections to the South Metro Area Regional Transit, or SMART bus system.

TriMet and the Oregon Department of Transportation sponsored a demonstration service on portions of this route as early as 1998. On Sep. 12-13, these trains operated in conjunction with the opening of the Westside MAX light rail line between Portland, Beaverton and Hillsboro. They connected with MAX trains at the Beaverton Creek light rail station using an adjacent freight spur. The trains used equipment provided by the Willamette & Pacific RR and the Pacific Northwest Chapter of the National Railway Historical Society.

The project has received both state and federal funding; construction began in October 2007, and included the reconstruction of every grade crossing along the route, as well as installation of new signals, concrete crossties and continuous welded rail. New double track sections were also added through Beaverton at the north end of the route, and Wilsonville on the south end. Construction crews also built a maintenance shop in Wilsonville adjacent to the rail station.

The project also included a major right-of-way relocation through downtown Tigard. The existing single-track former SP line was double-tracked, while the adjacent former BN (OE) line was removed. A new connection between the two lines was installed south of the Tigard stop, and a small freight yard was also built.

TriMet has purchased three single-level diesel multiple unit (DMU) railcars and a cab-equipped trailer coach from Colorado Railcar. The rolling stock will enable them to provide both one-car and two-car trains. The design is based on Colorado Railcar's Aero DMU, which demonstrated in the Portland area in November 2002. The first cars are scheduled to arrive in June 2008, with route testing to begin shortly thereafter.

The $117.3 million project is funded by:

$58.65 million in federal funding
$35.34 million from state lottery bond proceeds
$15.56 million from TriMet and GARVEE bonds
$7.75 million from local cities and Washington County
TriMet and Washington County are contributing a total of $4.1 million toward annual operating costs.

Meanwhile, officials in the Salem-Keizer area are looking into an eventual extension of this route all the way to Salem.