Hazmat rules generally cover "transportation in commerce" but do not clearly say where "transportation" begins and ends.
RSPA has proposed three possible approaches for determining boundaries: shipper intent, carrier control and custody, and movement on public right-of-way. The agency asked for comments on the alternatives last spring with a July 26 deadline, but had received only eight responses as of July 23. The new deadline is August 25.
Further discussion, including specific questions, can be found in the April 27 Federal Register available on the Internet at http://www.access.gpo.gov/su_docs/fedreg/a990427c.html