Terrorists are assholes.
Just... that's it, actually. I don't think I have anything else to say about them.
As to the target, it occurs to me that there's a strategic value to attacking mass transit, if you have an oil interest and want people dependent on individually owned and operated vehicles. But according to the news, while traffic has gotten worse, there's also been a big increase in bike sales. This is a nice thought. The bicycle=lovely two-wheeled middle finger to terrorists.