The load of sleepers was carried by a wagon type I had not previously seen. 31.70.4629.003-5 is a IFA sleeper carrier built by WH Davis in 2009, in a block of 50 wagons for Network Rail.
Similat DR 92616 coded as YXA(L), also by WH Davis, in 2004. This block of 50 wagons built in 2004.plus 15 in 2007, are considered to be part of the 'Track Renewal System' intended to operate with Matisa P 95 UK Track Renewal Machines in the DR 78801 series, but 41 were reported as stored at Kingmoor from 2015..
Previously sleepers for Westbury were typically moved on Salmon YWA wagons, which are expected to be retired shortly. It's possible that these sleepers were heading to Fairwater Yard, Taunton.