Safe Highways and Infrastructure Preservation Act - Amends Federal transportation law to prohibit a State from prescribing or enforcing any regulation that allows a restricted property-carrying unit (any trailer, semi-trailer, container, or other property-carrying unit longer than 53 feet, except for a fire-fighting unit) to operate on the National Highway System (NHS) (including the Interstate System), unless the operation of such unit is authorized by the State on June 1, 2003, and in actual and lawful operation on a regular or periodic basis (including seasonal operations) on or before that date. Prohibits a State from allowing the operation of a commercial motor vehicle combination on the NHS (except a vehicle or load that cannot be dismantled or divided easily, and that has been issued a special permit under State law) with more than one property-carrying unit (excluding the truck tractor) whose property-carrying units are more than: (1) the maximum combination trailer, semi-trailer, or other type of length limitation allowed by State law on June 1, 2003; or (2) the length of the property-carrying units of those commercial motor vehicle combinations, by specific configuration, in actual and lawful operation on a regular or periodic basis (including continual seasonal operation) in such State on or before June 1, 2003. Permits a commercial motor vehicle combination authorized in a State to continue to operate on System highways provided it is in compliance with State law, including routing-specific and configuration-specific designations and all other restrictions in force in the State on June 1, 2003. Amends Federal highway law to prohibit a State from allowing the operation of a vehicle or combination (other than a longer combination vehicle) exceeding Interstate weight limits on the Interstate System unless its operation was lawful: (1) on July 1, 1956; (2) in the case of the overall gross weight of any group of two or more consecutive axles, on the date of enactment of the Federal-Aid Highway Amendments of 1974; or (3) under a special permit pursuant to State (grandfather) law. Subjects such vehicles and combinations to all routing-specific, commodity-specific, and weight-specific designations in force in such State on June 1, 2003. Declares that Interstate weight limitations on vehicles and combinations (other than longer combination vehicles) that operate on the Interstate System shall also apply to such vehicles and combinations that operate on non-Interstate segments of the NHS, unless: (1) such segments are subject to lower State weight limits; or (2) a State allows the operation of any vehicle or combination on an existing non-Interstate segment of the NHS that could be so operated lawfully on June 1, 2003.