But the venture could be thrown into jeopardy by the departure of Peter Wood, chief executive at Direct Line, if RBS agrees to a takeover bid from one of its suitors.
Mr Wood has threatened to build a rival telephone-based insurer in Britain if RBS does agree to be taken over - hitting one of the bank's most profitable operations. In the six months to the end of March this year it delivered profits of pounds 45m.
RBS refused yesterday to deny that it was planning to merge with or be taken over by another bank, saying that it was not prepared to comment on market rumours.
However, fears of Mr Wood's possible break with the bank knocked 5p off the RBS share price of 524p.
Mr Wood's involvement in the US venture would be critical in that he would be spearheading the move, with Royal Bank of Scotland having a share of any profits from the new enterprise in return for its own participation.
Direct Line is now the UK's largest insurer, providing cover to some 2 million motorists and a growing number of home insurance policyholders. The company has also branched out into loans, mortgages and life insurance products.
One RBS source yesterday played down suggestions that if Mr Wood were to launch a rival operation it would be through Privilege Insurance, the company set up by him last year to target the 6 million non-standard motorists who cannot obtain cover through Direct Line.
"Privilege has been a phenomenal success and we have an interest in it, too. But let's face it, it has 50,000-odd customers compared to Direct Line's 2 million. You don't get volume in the direct market so easily or quickly any longer," the spokesman added.Reuse content