function removeDynamicAgents() {
  let allPassengers = surface.selectAll(".passenger").data(objects.passengers);
  let exitingPassengers = allPassengers.filter(function (d) {
    return d.state == "out";
  });
  exitingPassengers.remove();
  objects.passengers = objects.passengers.filter(function (d) {
    return d.state != "out";
  });
}