If you do that for 50 years, your risk is now almost 1%!
I am sorry, but the risk of dying from cancer, heart problems or car accident in the working life period of ages 20-65 lifespan is comparable to that 0,95% "composite subway terrorism" risk.
So if the security problems in Belgium continue, you should totally worry about it.
So yea, even if you ISIS continued to carry out a major terrorist attack on your subway every year for the next 50 years, it would still be a relatively tiny risk.
[0] http://well.blogs.nytimes.com/2007/10/31/how-scared-should-w...
However, most of your terrorism risk and car accident risk is before the age of 65. This is where they dominate.
Do you think that car accident risk is real? How much fatalities from car accidents were there in Belgium this year?
"Lifetime risk" is stupid metric, borderline fradulent. I don't care about dying at the age of 85, would welcome it after all. I'll care a great deal if my relative dies at the age of 30 or 40.
Also, one would have to accumulate an overall score, cancer, heart, terror. I'm quite sure all these factors are different per region.