Really easy method but a bit time consuming. Simply start one of the cab car services and drive to the first stop and come to a complete stop. Don't open the doors straight away before doing so save the game and then open the doors. This then means we don't have to keep setting the train up and driving to the first station. When the boarding task completes simply close the doors and exit to the menu. Once in the menu press on last played which should put you back in at the station meaning all you have to do is open the doors and then close them. Simply rinse and repeat this and the achievement is yours.