This post originally appeared on Orphan Road.

An article on planned streetcars in Tacoma includes this helpful FAQ:

Streetcars are smaller-capacity vehicles, operating at street level alongside pedestrians and autos, with frequent stops and easy access. A streetcar track requires less infrastructure and costs less because the cars are lighter. Cars can have a modern or a vintage trolley design.

Light rail is designed to carry more people quickly over longer distances. It typically has its own right-of-way and station platforms separated from traffic. Multiple rail cars may be joined together to increase capacity. Because light rail uses heavier cars, it needs a more expensive, heavier-duty infrastructure.

To which we can add that heavy rail, of the kind used by SF’s BART, NYC’s Subway, and DC’s Metro, requires a high-voltage “third rail,” to supply power, which makes it even more expensive — and dangerous.