Apart from the M4, the A48 had the largest number of cluster sites at 7 and there were no accident cluster sites on the M48 and the A449.
Ar wahân i'r M4, ar yr A48 yr oedd y nifer mwyaf o safleoedd clwstwr – 7 ohonynt, ac nid oedd unrhyw safleoedd clwstwr damweiniau ar yr M48 na’r A449.