The rumble of 1959 Chevrolets, once the rhythmic heartbeat of Havana, is fading to the near silence of electric vehicles as the island faces its worst fuel shortage in years.

For six decades, Cuba’s roads changed little, defined by colorful vintage cars. But in recent years, Cubans increasingly adopted electric vehicles as fuel became more scarce. Now, they are helping the population grapple with a worsening fuel crisis, since the U.S. cut off oil exports from the communist-run country’s ally Venezuela and threatened to penalize other countries exporting fuel to the island.

Donald Trump’s administration has declared Cuba “an unusual and extraordinary threat” to U.S. national security.