The provisions of 28 U.S.C. 2679(b) provide that the remedy against the United States, as provided by sections 1346(b) and 2672 of title 28, for injury or loss or personal injury or death resulting from the operation by an employee of the Government of any motor vehicle while acting within the scope of his employment is exclusive of any other civil action or proceeding by reason of the same subject matter against the employee or his estate whose act or omission gave rise to the claim.