Seattle Transit Blog reports that beginning in October, Metro and Sound Transit will extend their service routes to provide an alternative to paying a toll once the SR 520 bridge becomes a toll bridge next spring. Metro will add service to routes 255, 265, 271, and 311; Sound Transit will debut a new express route (542) between the University District and Redmond.

Via Seattle Transit Blog (emphasis mine):

According to the SR 520 and SR 522 Service Implementation Plan, tolls are expected to increase transit demand by 15-35%. A recent poll suggests that tolls will encourage transit use, with 16% of respondents choosing transit as one of many alternatives to tolls. That figure increases to 22% if both 520 and I-90 were tolled. Currently, 15,000 riders cross the 520 bridge every day. Routes 255 and 271 together provide 4,300 crosslake trips each weekday.