To better serve its growing transit ridership, Seattle’s Sound Transit will launch improvements and changes to its ST Express regional bus and Sounder commuter rail service starting Sept. 20.

Seventeen of Sound Transit’s 24 ST Express routes will see changes, such as new trips to increase frequency, minor schedule adjustments or major rerouting to places like new transit facilities. A new route will also be added to connect the recently completed Lakewood Station with the Tacoma Dome Station.

Additionally, more Sounder trains will serve both the north and south corridors, while three new roundtrip trains will be introduced.

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.