How pedestrian WALK and DON’T WALK signals evolved?

1. Separate Pedestrian Phase: In 1930, all 4 approaches of the intersection had a separate phase so pedestrians can walk in all directions including diagonally

2. RED-YELLOW-GREEN-WHITE: 4th signal indication of white with black background for pedestrians to cross the intersection

3. WALK and WAIT: MUTCD (USA) was first to implement WALK and WAIT signals at the intersection corners

4. WALK and DON’T WALK: In 1961, MUTCD removed WAIT as it easily be mistaken as it resembles WALK letters and followed DON’T WALK