There have been long-standing and extensive efforts to reduce deaths in traffic accidents too (in fact over time far more extensive than our antiterrorism efforts), and yet in the month of September, 2001, 20% more people in the US died in traffic accidents than in acts of terrorism. Once you aggregate beyond a year, the risk of terrorism is insignificant.

If you don't believe that, let's stop enforcing traffic safety laws, stop requiring manufacturers to include safety features in their cars, and stop designing traffic intersections with safety in mind and see what happens.