The Queen and the Duke of Edinburgh are among the very first to travel on one of the new high speed Hitachi trains being built for the region.
It was a milestone for the massive project to upgrade the Great Western network.
The scheme aimed at easing some of the worst crowding in the country remains late and over budget.
But the new trains will start to enter service later in the year.
They will eventually run from Paddington to Reading, Newbury, Didcot, Bedwyn, Swindon, Bath, Bristol and through to Wales and Devon and Cornwall.
Our Transport Correspondent MIke Pearse has been talking to commuters who say the improvements can't come soon enough.
Mike spoke to Paul Gentleman from Great Western Railway and Chris Irwin from Travelwatch South West.
Incident at Southall causes disruption on GWR between Reading and Paddington: