Mae arfarniad trafnidiaeth cam 1 a ystyriodd yr effeithiau amgylcheddol a hefyd sut yr oedd polisïau’n cyd-fynd â’i gilydd wedi’i gynnal mewn perthynas â’r holl lwybrau yr ydym yn eu cynnig. Craffwyd ar yr allyriadau CO2, a gwnaeth y dadansoddiadau ystyried cymariaethau rhwng teithio yn yr awyr ac ar y llawr (ee car a thrên). Gwelwyd nad oedd gwahaniaeth mawr rhwng y dulliau teithio o safbwynt yr allyriadau carbon fesul km gan deithwyr.
A stage 1 transport appraisal considering policy compatibility and environmental impacts has been undertaken on all of the routes we are proposing.  CO2 emissions were scrutinised, and the analysis looked at comparators between air and surface routing (eg car and train).  The relative passenger/km carbon emissions were not considered to be materially different between the modes.