Boston's Green Line D Branch has a lot in common with San Diego's Trolley, the first modern light rail system in the United States.

 https://www.youtube.com/watch?v=JCBg2sFPtis It's also 22 years older. So...does that make it the true first modern light rail in America? 

https://en.wikipedia.org/wiki/Green_Line_D_branch

https://www.mbta.com/schedules/Green-D/line