Student or Learner
dear all in this sentence
people kept colliding on the stairs
i've not understood kept colliding
Bumping into each other - perhaps quite hard.
If I am running down the stairs and get to a bend, while you are running up those same stairs and get to the same bend, we may collide if we don't hear each other and slow down/move aside to let the other person pass.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.