Two things.

1) This is a fantastic reaction to any act of terror at any time. It is hard to not be affected when things like this happen; it is scary, especially as it feels more frequent. In those times, it is advisable to take a stance like this one:

2) Philadelphia fears, ranked:

  1. Hit by a SEPTA bus / trolley
  2. Neighborhood becomes “new Northern Liberties”
  3. Vehicle fire on 76
  4. Mummers parade / Wing Bowl
  5. Subway grate / basement doors collapse while walking on them