A list I found at

http://www.impulsenc.com/html/proj_reference.htm

seems to indicate municipal transit systems typically use
600VDC.

Seattle used dual mode busses that ran electric (from a two line catenary) underground, and diesel on the surface.

TTC in Toronto, Canada, and probably many mass transit systems, are looking to expand with underground busways
(no track or physical interlock to lay and maintain).