def add_stop_capacity_type(stops_df):
    """
    adds capacity_type column which is defined
    with the following dictionary using the StopType
    Bus stops are low capacity, train stations are high
    capacity. 
        Parameters:
        stops_df the dataframe want to add the column to
    Returns:
        dataframe with new capacity_type column
    """

    dictionary_map={"RSE":"high",
                    "RLY":"high",
                    "RPL":"high",
                    "TMU":"high",
                    "MET":"high",
                    "PLT":"high",
                    "BCE":"low", 
                    "BST":"low",
                    "BCQ":"low", 
                    "BCS":"low",
                    "BCT":"low"}

    stops_df["capacity_type"]=stops_df["StopType"].map(dictionary_map)

    return stops_df