def check_road_length(length):
    """
    Determine the key for where to store the road length.
    """

    key = ''

    if length <= 20:
        key = '0-20'
    elif 20 < length <= 40:
        key = '20-40'
    elif 40 < length <= 60:
        key = '40-60'
    elif 60 < length <= 80:
        key = '60-80'
    elif 80 < length <= 100:
        key = '80-100'
    else:
        key = '100-'

    return key