Magistrates in Ely also fined the Duke (60) £60 and ordered him to pay £35 costs.
The Duke is also to lose his membership of the IAM, the organisation said today.
But the institute has yet to decide whether the Duke will have to step down as the organisation’s president.
The Cambridgeshire court heard that the Duke had accumulated 12 penalty points on his licence after being convicted of four speeding offences in the past three years.
The Duke admitted the latest offence – at Thorney, Cambridgeshire, in August – when he was caught travelling at 70 mph on a road with a 60 mph speed limit.