Weekend trips to cities like Boston, Chicago or San Francisco rarely require a rental car to get around, given their extensive public transportation systems. But more unexpected locales are joining the car-optional list as new and expanding rapid transit options take root across the country.

Many major transit systems, like those in New York, predate the ubiquity of cars and serve densely populated urban areas. Now, younger and less dense cities, like Denver, are adding trains or streetcars. Even places most closely associated with cars, like Detroit and Los Angeles, are remaking transit networks once ripped out to make way for Fords, Chevys and Chryslers.

“It’s interesting to see how the West in particular is growing and expanding public transportation,” said Virginia Miller, a spokeswoman for the American Public Transportation Association.

The nonprofit group reported that 69 percent of public transportation initiatives on ballots nationwide in the November 2016 elections were approved, for a total of about $170 billion in transit projects.