Sound Transit Express

Sound Transit Express (ST Express) is a network of regional express buses operated by the multi-county transit agency Sound Transit. The routes connect major regional hubs throughout 53 cities in three counties (King, Pierce, and Snohomish) in the Puget Sound region. Sound Transit Express ranks first in the nation in the number of commuter bus passengers carried and in vehicle miles driven. The first nine routes and 114 buses began carrying passengers on September 19, 1999. In 2025, the system had a ridership of 9,809,600, or about 30,000 per weekday as of the first quarter of 2026.

Unlike a typical transit bus service, Sound Transit Express routes typically make limited stops as they travel longer distances on the freeways. Most routes operate seven days a week, with runs throughout the day. Where available, buses use transit-only lanes, high-occupancy vehicle lanes, high-occupancy toll lanes, express lanes, bus bypass shoulders, and direct access ramps to speed travel times. The enabling legislation for Sound Transit requires the eventual replacement of interim express bus routes with forms of high-capacity transit, including Link light rail and bus rapid transit. As a result, many routes have been truncated or discontinued to accommodate expansions of the regional transit system.

While Sound Transit oversees, plans, and funds the service, operation and maintenance of the buses is contracted out to Community Transit, King County Metro and Pierce Transit. There are 240 buses in the system's fleet.