[3] AC Transit introduced a separate Dumbarton Bridge transbay service, route U, on August 29, 2004.

It was replaced with AC Transit route DA between Ardenwood and Redwood Shores, which operated until December 15, 2013.

[13][15][16] By 2009, some reverse-peak trips (eastbound in the morning and westbound in the afternoon) were routed via East Palo Alto and designated DB3.

[17] On December 19, 2011, route DB3 was discontinued, and MV Transportation replaced AC Transit as the operator of Dumbarton Express service.

[20] On August 2, 2017, SamTrans released a study that examined the feasibility of adding additional bus routes to the service.