1. I don't consider the current situation in the US "terror". I'm talking about different times and places. If you were boarding a bus in Israel, Sri Lanka, Iraq during certain periods of time, you would have a higher chance of dying from a bombing than from an accident.
2. The natural response to terror is anything but rational. It is a completely different feeling to go on a bus knowing there's a possibility of an accident to going on a bus knowing that one of the passengers may be carrying a bomb.
You should check the stats on these things first. I'm pretty certain that isn't true. Check out the traffic fatality rate in Iraq: http://chartsbin.com/view/0lz
Even with the rate of Israel at 7.59 per 100,000, that comes out to 539 people per year.
http://www.wolframalpha.com/input/?i=population+of+israel+*+...
That is more people every year than have died of terrorism in any year during Israel's history, even 1948. http://www.mfa.gov.il/MFA/MFAArchive/2000_2009/2000/1/Terror...
Even in the most terrorism-stricken places on earth, traffic fatalities still dwarf terrorism.
In any case, the stats are meaningless, as they have nothing to do with human nature and the way we perceive odds & danger. When the Beltway sniper was operating I don't think anyone was calmed by the knowledge their chances of being hit are really quite small.
I would compare the feeling to the feeling of wanting to do something, but not having the guts to just 'do it.' In this case, you want to search everyone on the bus that you don't trust until you are satisfied there is no bomb, but social pressures prevent you from doing so. This causes the stress.
The difference just being acceptance. When you believe that someone may be carrying a bomb you hold onto some hope that something can be done to stop them. When you get on a bus knowing that there is the possibility of an accident, there's not much you can do short of wrestling for control of the bus from the driver (or just not getting on the bus).
People have accepted that accidents happen. People have not accepted yet that 'terrorism' is a fact of life.