def bus(informed_entity):
    """Decodes informed entity objects for buses and returns a human-readable route name

    Args:
        informed_entity (dict): The informed entity object returned by the API for a bus route

    Returns:
        str: The route ID
    """
    route_id = informed_entity["route_id"]

    # handle night buses
    if len(route_id) == 4 and route_id[:3] == "991":
        return "N" + route_id[-1]
    elif len(route_id) == 4 and route_id[:2] == "99":
        return "N" + route_id[2:]

    else:
        express_route = route_id[-1] == "1"

        route_id = route_id[:-1]
        if express_route:
            route_id += "e"

        return route_id