Effect of terrorism on transit

I have been wondering ever since 9/11 what the effect of terrorism was going to have on mass transit. Planes and trains are vulnerable because the results can be spectacular and the casualties can be high - both very important for terrorists looking to draw attention. Palestinian bombers targeted bus stations, too. Even in the absence of terrorism, the threat raises the cost of using mass transit because of intrusive searches and inconvenience of additional security precautions (the convenience is usually one of the biggest assets of subway systems).

On the other hand, when mass transit is a terrorist target and cars are expensive (especially in dense cities), people still have other choices like walking and cycling. It looks like that is the preferred solution in London at the moment. I wonder if this would be the opportune time for the owners of Segway to go public? And what other transport ideas would be a good investment?

How about a hydrogen-powered motorbike?