Simplify the following text for a Grade 5 native English-speaking person.
Original: In addition , during the ' 35 â `` '36 seasons the inside wall was removed in the corners , the angle of the outside wall in relation to the track was changed to keep cars from launching over , hard crash helmets became mandatory , and the first yellow light system was devised around the track .
Simplified: The outside wall angle was changed to help keep cars inside the track . Hard crash helmets became required .