According to Trailer-bodybuilders.com:

The National Highway Traffic Safety Administration (NHTSA) issued a Notice of Proposed Rulemaking (NPRM) proposing to place a requirement in the Federal Motor Vehicle Safety Standards (FMVSS) that motor vehicles 10,000 lbs. gross vehicle weight rating (GVWR) and below, excluding walk-in vans with an automatic transmission that includes a “park” position, manufactured for sale after Sept. 1, 2010 be equipped with a brake transmission shift interlock (BTSI).

This interlock will require that the service brake pedal be depressed before the transmission can be shifted out of “park” and will function in any starting system key position.

NHTSA is issuing this document in response to a statutory mandate in the Cameron Gulbransen Kids Transportation Safety Act of 2007.

Based on changes to which type of vehicles would be covered by the regulation, low-speed vehicles would have to meet this proposed requirement. Learn more:  Trailer-bodybuilders.com