Apart from the M4, the A40 had the largest number of cluster sites at 5 and there were no accident cluster sites on the M48.
Ar wahân i'r M4, ar yr A40 yr oedd y nifer mwyaf o safleoedd clwstwr - 5 ohonynt, ac nid oedd unrhyw safleoedd clwstwr damweiniau ar yr M48.