code: @Pure
  	public double distanceToBusStop() {
  		final Point2d  p1 = getPosition2D();
  		if (p1 != null) {
  			final BusStop stop = getBusStop();
  			if (stop != null) {
  				final Point2d p2 = stop.getPosition2D();
  				if (p2 != null) {
  					return p1.getDistance(p2);
  				}
  			}
  		}
  		return Double.NaN;
  	}
docs: Replies the distance between the position of this bus itinerary halt
  and the position of the bus stop associated to this bus itinerary
  halt.
  
  @return the distance between the position of this bus itinerary halt
  and the position of the bus stop associated to this bus itinerary
  halt.
  @since 2.0