The figure that jumps in front of Travis's truck is seen wearing a hooded raincoat or robe.
My theory is that it is a mental projection from Alessa, and not physically someone.
Some people believe its Helen or Dahlia.
Dahlia is seen at her house, which is a ways down the road, and wouldn't have enough time to dart in run from there, across the road, and back to her house where Travis sees her hiding behind around the corner.
And Helen is either dead, or, if the Sanitarium is still up and running ( which is unclear in the game if it is, is still locked up there, so there is no way it could've been her.

^ It's a mental projection by Alessa, like she did too Harry in SH1, it's the same clothes she wears everywhere else in the game.

Thanks for the link Bishop