public DirectionsApiRequest trafficModel(TrafficModel trafficModel) {
    return param("traffic_model", trafficModel);
  }
Specifies the traffic model to use when requesting future driving directions. Once set, you
must specify a departure time.

@param trafficModel The traffic model for estimating driving time.
@return Returns this {@code DirectionsApiRequest} for call chaining.
src/main/java/com/google/maps/DirectionsApiRequest.java