Robot Moves forward
Detect Left lane and Right lane, calculate angle and distance comparing them to decide if needs to turn or forward.
Robot Turns Left
Detect Right top lane and distance. If distance is near enough, then turn left. Since Top lane is at right side, so Robot needs to turn left, otherwise turn to right.
Robot Moves forward after turning
Turn left after several seconds, depending on speed, then check Right Lane, if Right lane angle is bigger than 70 degree, moves forward.