Originally literal ('tailwind vehicle' — a favorable lift). The ride-share sense was popularized by
滴滴顺风车 and
嘀嗒出行. Distinct from
网约车 (commercial ride-hail) and
拼车 (splitting a cab). The figurative sense uses
搭 —
搭上...
的顺风车 = 'ride on the wave of ...'.