Sound Transit announced Monday it will launch improvements and changes to ST Express regional bus and Sounder commuter rail service starting Sat., Sept. 20, to serve growing numbers of transit riders. The changes include a new ST Express route, changes to 16 routes, deletion of one ST Express route, and more Sounder commuter rail trains serving both the south and north corridors.

Seventeen of Sound Transit’s 24 express bus routes will see changes, such as new trips to increase frequency, minor schedule adjustments or major rerouting to places like new transit facilities.

New ST Express Route 599 service will begin connecting Sound Transit’s newly completed Lakewood Station with Tacoma Dome Station starting on Monday, Sept. 22. The new route will give Lakewood residents a smooth and easy connection to Sounder commuter rail service until Sounder service reaches South Tacoma Station and Lakewood Station by 2012.

In addition to Sounder connector service, the opening of Lakewood Station will add 22 trips to the popular ST Express service between Seattle and Lakewood on ST Express Route 592.

The Sounder commuter rail schedule will expand with three new round-trip trains starting Monday, Sept. 22. Two new weekday round trips on Sounder’s south corridor include a sixth peak-direction train and the second reverse-commute train. Sounder’s north corridor will see a fourth round trip, with schedule changes that will improve the coordination with ferry schedules to better serve the new Mukilteo Station.

Last week, Sound Transit’s latest ridership numbers showed an overall 25 percent increase in ridership from July 2007 to July 2008 — five times higher than the national growth rate for transit ridership in the second quarter of 2008. Sound Transit’s growth included a 38 percent increase on Sounder commuter rail. Additional information is available at http://www.soundtransit.org/x8922.xml .

Complete information about the Sound Transit schedule and route changes that get underway on Saturday can be found at http://www.soundtransit.org/x115.xml .

Tacoma and Pierce County changes include:

— ST EXPRESS BUS SERVICE —

— ST Express Route 574 (Lakewood-SeaTac): One southbound trip added and minor schedule adjustments;

— ST Express Route 582 (Bonney Lake-Tacoma): One eastbound and one westbound trip discontinued due to low ridership;

— ST Express Route 586 (Tacoma-U. District): Stop added in U-District at NE 40th Street;

— ST Express Route 590 (Tacoma-Seattle): 19 trips added; schedule adjustments;

— ST Express Route 591 (Lakewood/Tacoma-Seattle): Route discontinued; trips replaced by added trips on Route 590 and Route 592;

— ST Express Route 592 (DuPont/Lakewood-Seattle): Stop added to serve Lakewood Station; major schedule adjustments; 22 trips added;

— ST Express Route 594 (Lakewood/Tacoma-Seattle): Stop added to serve Lakewood Station;

— ST Express Route 599 (Lakewood Station-Tacoma Dome Station): New route travels between Lakewood Station and Tacoma Dome Station to connect to Sounder commuter rail; this route will use Pierce Transit buses;

— COMMUTER RAIL SERVICE —

— South line: Two round trips added; minor schedule adjustments.