You say that like there's a rational security analysis behind TSA's policies in airports. But yeah, planes have a nasty habit of offering to amplify an attack

You say that like there's a rational security analysis behind TSA's policies in airports. But yeah, planes have a nasty habit of offering to amplify an attack of a certain magnitude by falling out of the sky and killing everyone on board, and potentially quite a few not on board. Trains just doesn't do that. The 7/7 attacks in London (bombs on three trains and a bus) resulted in probably an order of magnitude less loss of life than the same bombs on planes would have.