While these data are the most detailed and reliable source of information on road collisions and casualties, they do not provide a complete record of all such incidents.
Er mai’r data hyn yw’r ffynhonnell wybodaeth fwyaf manwl a dibynadwy am wrthdrawiadau ac anafiadau ar y ffyrdd, nid ydynt yn rhoi cofnod cyflawn o’r holl ddigwyddiadau o’r fath.