Intercity bus ridership has especially thrived in the New York City region, in part as more buses offer people a wider choice of pickup and drop-off locations and significantly lower fares than trains. The city’s strong job market has also drawn long-haul commuters from Pennsylvania, southern New Jersey, upstate New York and elsewhere. In 2018, there were an estimated 22 million intercity bus rides in the New York City area alone, or about a million more rides than in 2014, according to Mr. Schwieterman.

Buses are “a solution to the congestion problem” since they offer an alternative to driving, said Peter J. Pantuso, the president and chief executive of the American Bus Association, an industry group. But, he added, cities have been slow to invest in new terminals and infrastructure as they “have identified they have challenges, but they haven’t quite figured out how to address them yet.”

The Port Authority, the country’s busiest bus terminal, opened in 1950 in part to help reduce congestion. Today, all 186 active passenger boarding areas — spread over three floors in two buildings — are full during peak hours. A larger terminal is planned, though it is years away. For now, 18 bus companies and New Jersey Transit share the terminal.

Megabus is not one of them because its double-decker buses are too tall to fit. So passengers wait to be picked up at a bus stop on the Far West Side where there is no bathroom, food court or shelter from the cold and rain. Still, they keep coming. Since the carrier started in New York in 2008, ridership has tripled, and routes have expanded to 38 cities from six.

Sean Hughes, a spokesman for Megabus, said the carrier has worked to address community concerns about congestion and idling, including offering drivers bonuses for not idling.

Today, there are 118 curbside bus stops in Manhattan, according to the city, of which 66 are clustered between 14th and 59th streets in neighborhoods that are already overrun with cars. In total, the Manhattan stops are used hundreds of times a day by private buses — on a recent weekday passengers were dropped off 946 times and picked up 799 times.