Ym mis Mawrth 2012, lansiais wasanaeth T4 newydd rhwng y Drenewydd a Merthyr sy'n mynd yn ei flaen wedyn i Gaerdydd, drwy fuddsoddi oddeutu £1m mewn chwe cherbyd newydd, llawr isel. Ers ei gyflwyno mae nifer y teithwyr ar y gwasanaeth wedi cynyddu fwy na 22%.
In March 2012, I launched a new T4 service between Newtown and Merthyr with onward travel to Cardiff with investment of round £1m in six new, low floor vehicles. Since its introduction the service has seen passenger numbers increase by more than 22%.