Complex sentence: The campaign group Friends of Suburban Bristol Railways held a celebration of the passenger increase in 2009, in conjunction with students from Parson Street Primary School who had provided artwork to brighten up the station.
Split into simpler sentences: The campaign group Friends of Suburban Bristol Railways held a celebration in 2009 to mark the increase in passenger numbers. They were joined by pupils from Parson Street Primary School who had provided artwork to brighten up the station.