Houjun Liu

Ambulance Trajectories

Problem: current ambulance routing don’t optimize significantly on the contextual cases for stroke patients

Stroke hospitals: PSC is smaller than a CSC.

Previous work

Routing methods—

  • route all patient to nearest PSC, which is worse than
  • route high risk patient to CSC, which is worse than
  • always route to CSC

This is counter-intuitive. How do we solve, given a stroke condition, available PSC/CSC locations, traffic, etc., for where and how to route a patient?

Ambulance MDP formulation

  • \(S\): (location, symptom onset, known stroke type, stroke type)
  • \(A\):
    • route to clinic, route to [specific] PSC, route to [specific] CSC
    • will never be downrouted (for instance, if you are at a PSC you will always either stay or go to CSC)
  • \(T(s’|s,a)\):
    • location changes
    • distance
  • \(R(s,a)\):
    • “probability of patient outcome” \(P(success|time)\) (Holodinsky, et. al. 2018)
    • if stroke type is unknown, its a weighted average


Forward Search, depth of 2: patient will either get transported or bounced and transported.


  • status quo: people near Stanford hospital/ChanZuck are better
  • MDP: smoother gradient