You are far more likely to die in a car crash than by terrorist action. Does this prevent you from getting in your car?
With the understanding that the numbers have increased, between 2004-2013, 80 Americans were killed in terror attacks. If we include data from 9/11/2001 onward, the number increases to 3,066.
There were 29,989 fatal car accidents in the United States in 2014 alone, in which 32,675 deaths occurred (source: Insurance Institute for Highway Safety).
So even understanding that the 3,066 number does not include yesterday's attack, and does not include non-terror-affiliated gun violence, it's still pretty clear that cars are more dangerous by the numbers.