The move will see Wales become the first UK nation to introduce a lower speed limit following in the footsteps of European countries, such as Spain, where 30km/h (18.5mph) is already in place.
Bydd hyn yn golygu mai Cymru fydd cenedl gyntaf y DU i gyflwyno terfyn cyflymder is gan ddilyn ôl troed gwledydd Ewrop fel Sbaen lle mae 30km/h (18.5mya) eisoes ar waith.