Network Rail has also now determined that the intended line speed increases cannot be achieved in the middle of the line because of two existing level crossings.
Hefyd, mae Network Rail bellach wedi penderfynu na ellir cyflawni'r cyflymderau llinell uchel a fwriedir yng nghanol y llinell oherwydd dwy groesfan reilffordd sy'n bodoli eisoes.