The poem makes one clear allusion, which appears in the second stanza (lines 8-10):

[...] The truth,
he said, was blowin' in the wind,
or round the next bend.

"Blowin' in the Wind" is a 1962 song by Bob Dylan, and one of the key anthems of the 1960s folk revival and counterculture movement. It's a song about freedom, peace, and the folly of humankind. (Earlier in the stanza, "following the sun from west to east" might also allude to Dylan: the chorus of his famous 1968 song "I Shall Be Released" begins, "I see my light come shining / From the west unto the east.") Within the poem, the Dylan allusion portrays the hitchhiker as a hippie-like character. He doesn't buy into the speaker's conventional workaday lifestyle.

Note, though, the hitchhiker's reference is a little dated. The Vauxhall Astra didn't come out until the 1980s, so there is no way this poem can be set in the 1960s. By this point in the 20th century, capitalist consumerism has largely won out over the idealistic longing of the hippie movement. Perhaps that's partly what enrages the speaker about the hitchhiker.

It's not clear whether it's the speaker or the hitchhiker who says "round the next bend." Either way, it ties in ironically with the main allusion. Perhaps it's a little quip made by the hitchhiker to try and break the ice with the stranger driving the car. Or maybe it's the speaker's own joke to himself. But it's "round the next bend" that the speaker suddenly assaults the man and leaves him for dead. This, in a way, is the speaker's answer to the rhetorical questions posed by a song like "Blowin' in the Wind": he perpetuates the same kind of senseless violence the song critiques.