For example, 35 people died in the Brussels Metro attack. Inshallah that's the only attack on the Brussels Metro this year.
That's 35 out of an annual ridership of 135 million. [0] Thus the chance of you being a victim on any particular journey is 35/135 million. If you take the subway twice a day, your likelihood of being a victim of a terrorist attack is 0.019%. It's just not a real risk.
What really annoys me is that they already include the crime rate is a separate consideration. Is terrorism not a crime? I don't particularly care if I die at the hands of a suicide bomber or a random mugger, so it doesn't make any sense to dramatize the risk of the former when it can already be captured in the standard crime rate.
[0] http://www.stib-mivb.be/figures.html?l=en
[1] http://www.wolframalpha.com/input/?i=35%2F135+million*365*2