Most of the changes are to accommodate earthworks, topographical conditions or to tie in with accommodation works and have been constructed.
Diben y rhan fwyaf o’r newidiadau yw addasu ar gyfer cloddwaith, amodau topograffig neu i gyd-fynd â gwaith addasu ac maent wedi cael eu hadeiladu neu maent wrthi’n cael eu hadeiladu.