Jan 2 - Standard & Poor's Ratings Services said today that its ratings and outlook on Parsippany, N.J.-based car renter Avis Budget Group Inc. (B+/Stable/-) are unaffected by the company's announcement that it has agreed to acquire car sharer Zipcar Inc. (not rated) for approximately $500 million, primarily using debt. Zipcar's hourly car sharing, which would be a new business for Avis Budget, generates lower margins than Avis Budget's daily car rental business. However, the company expects t