function vmax = region_free(world_state, start_state, len, P)

vmax = 0;
for k=1:length(P.cars)
  state = world_state.car_states(k);
  if state.road_id == start_state.road_id && state.lane_id == start_state.lane_id ...
        && state.x > start_state.x && state.x < start_state.x + len
    vmax = max(vmax, state.v);
  end
end
