It's like bit fields.

BIT_LANE_USE_STRAIGHT = 000
BIT_LANE_USE_SLIGHT_RIGHT = 001
BIT_LANE_USE_SLIGHT_LEFT = 010
BIT_LANE_USE_RIGHT = 011
BIT_LANE_USE_LEFT = 100
BIT_LANE_USE_SHARP_RIGHT = 101
BIT_LANE_USE_SHARP_LEFT = 110
BIT_LANE_USE_UTURN = 111

That being said, I'm considering removing those fields, since they probably won't be used.