A date for the inquiry, which follows objections from the public to the proposed alignment, will be announced later this year.
The new A1073 would run for 19km from the Spalding area to Peterborough.
Mr Speechley (Con) was convicted of misconduct in public office after he failed to declare an interest while seeking to influence the alignment in a way that could have increased the value of land he owned in Crowland.
Compulsory purchase orders have been sent to owners of affected properties.
Mr Croft said: 'Both the director of highways and planning and the county secretary and solicitor assure me that in their opinion the decision is sound.'
Mr Speechley remains a councillor pending an appeal against his conviction and 18-month sentence.