Not to say that it would be EASY to pull off, but as far as the tensile strength of certain kinds of spider webbing go–specifically that of the Darwin’s bark spider–stopping a subway train might be “amazing”, but it’s by no means absurd.
A group of students at the University of Leicester (on the heels of another academic who recently built a “spider sense suit”) determined that to stop a train as in the famous scene from Spider-Man 2, the webbing would need to absorb approximately 500 million joules of energy to withstand 300,000 Newtons of force without snapping. All it needs is to be properly anchored–and get this: Only ONE strand of spider silk would be necessary, not the multiple strands Spidey uses in the film (though I have to applaud his erring on the side of caution). It just HAS to be the Darwin’s bark spider, whose silk is 10 times stronger than kevlar.
As one of the study’s (charmingly titled “Doing Whatever A Spider Can”) three authors, Alex Stone puts it:
“It is often quoted that spider webs are stronger than steel, so we thought it would be interesting to see whether this held true for Spider-Man’s scaled up version. We were surprised to find out that the webbing was portrayed accurately.”
Fascinating….But I admit I have my doubts: Someone get Mythbusters on this!
Source: The Mary Sue