MBTA Searches: Constitutional?

Inspired by poot's comment in a prior thread, I went to FindLaw.com and did my own search.

All I was able to come up with were the following three cases:

United States v. Drayton et al
Florida v. Bostick
Florida v. Rodriguez

The thrust of which is that police can ask to search persons on public transportation, but that the passengers have a fourth amendment right to refuse the search. No surprise there. I honestly don't think that there is any precedent for whether refusing to submit to a search means that you can be denied access to public transportation.

I tend to think that a screening requirement would be completely legal and would not violate the fourth amendement, provided that all passengers are subject to the same scrutiny. The problem that I have with the MBTA's plans are that they don't intend to search everybody, and I don't believe that there is any way that the searches can be "random." This is the only problem I have with their plans.

In a practical sense, it can't be done. Everyone knows that it takes forever to screen 100 people on an airliner. Screening over a million people who take public transportation in Boston each day is impossible. I guess we won't know what the legal answer is unless the National Lawyers Guild goes through with its lawsuit.