The poem is written in five line stanzas with very occasional rhyme of lines 3 and 5 and variable lengths. Occasionally internal rhyme helps to emphasize a key word: eg. 'hair' and 'fair' stresses the joke about the victim's hair and 'tired' and 'fired' may provoke some sort of reason for the killing.
The conversational tone is helped by the use of the dash in the third stanza to mirror the natural pause in speech. There are also a number of minor sentences - 'it was hired' and 'it was twelve noon'. Many which begin quite simply with the subject: 'I'd been', 'I thumbed', 'I picked', 'I let him', 'I dropped it', 'We were', 'He'd said', 'It was', etc. These help to emphasise the man's unhealthy obsession with 'I' (himself).
The simple sentence patterns also add to the normality and simplicity of the tone of the poem - which is even more disturbing as the killing is then conveyed as a very simple and normal action as far as the killer is concerned - the lack of nerves, exitement or regret is particularly frightening. The driver seems more interested in the time and the weather than the murder victim.
The 'cheerful' triple rhyme in the first stanza (tired, fired, hired) and the final stanza (hair, fair, there) again provides an ironic contrast with the dark violence of the poem. Disturbingly, the rhyme may reflect the cheerful attitude of the killer after the deed has been carried out.
The kanguage is very ordinary and conversational which makes it even more frigtening to think that psychopathis killers can be quite ordinary people.
So the man uses everyday clichés such as 'under the weather' and he jokingly imitates the boring language of weather reports, ' the outlook for the day was moderate to fair'. This also places the murder in very ordinary weather, showing that it can happen at any time.
He even uses ordinary, mundane language for the actual murder: 'I let him have it' and polite (euphamistic) language: 'he leant across 'to let him out'. This is all darkly ironic as he is not helping the man out of the car ut instead pushing his body out of a moving car. The man's calm and plain language reflects his lack of and emotion (particularily his lack of anger) - and this makes him seem even more disturbed, especially if he is seen as joking about what he has just done. He does not see his actyions as anything out of the ordinary.
He creates a cartoon-like picture in the reader's head by describing the hitcher, 'bouncing off the kerb' and by viewing it through the mirror as if the killer is distanced from feeling any sympathy for the victim.
The fact is that his victim is completely random and killed for no particular motve makes the man's violence even more unpredicatable and therefore, more sinsister.
The man jokes ironically that the hitcher said he 'liked the breeze' in his hair - and of course this is what he gets from the driver. The driver also mocks the hitcher's hippy lifestyle ('the good earth for a bed') and beliefs : 'the truth/ he said was blowin' in the wind'. This line mimics the 1960's Bob Dylan song, 'Blowin in The Wind'.
It is as if the driver, trapped as an office worker, is jealous of the freedom of the hitcher. So, the driver adds, ironically, that the 'truth' will be 'round the next bend' - where he kills the man.
The driver seems jealous of the hitcher's romantic outlook on life and Armitage uses some mundane names ans objects to contrast with the romantic views of the traveller. So he mentions ordinary, plain English place name like 'Leeds' and 'Harrogate' and ordinary brand names like 'Vauxhall Astra' and 'krooklock'. These give an anti-romantic feel to the driver's attitude and contrast with the romantic idea of 'following the sun to west from east'.
The poest also sprinkles ironic puns throughout the poem to build up dark humour.
The warning from his boss about his 'sick-note' to explain his many abscences points to the fact that this man is mentally 'sick' in the poem. Or that he is sending 'sick' notes.
The driver is proud of his actions and even brags that he 'didn't even swerve' when carrying out the attack. His self-control again helps to create a more chilling and callous persona.