See:
http://news.bbc.co.uk/1/hi/wales/6961046.stm
" "From December this year Arriva Trains Wales takes delivery of an additional 18 carriages and the longer platforms will allow these to be added to our busiest commuter trains"
There are longer platforms being installed at Pontypridd, and presumably elsewhere... what class will these 18 new carriages be - more 150s?