Well, I got a reply from Pennsylvania DOT, saying they were referring my questions to the Federal Regulations Unit in Harrisburg.
Not wanting to wait for a phone call or an email from them, I sent a request to the Federal DOT for clarification and got a reply saying they forwarded my email to the National Transportation Library Reference Service in the Bureau of Transportation Statistics for answering.
LOL -
There may not be an official answer, at this rate, but I'll hang in there.
Larry