Line services from Regional Railways to allow Class 158 units to be converted to Class 159s for the West of England services. Their operation in the Bristol area is slightly different. All services in the Bristol area have guards and will in the future so the trains will not be driver only operated at all in the Bristol area. The practice of the opening/closing of the doors is also different, in which the driver releases the doors which are then closed by the guard. All 166 units now have local door panels fitted in at the doors of the end coaches, this is to allow the units to stop at stations with short platforms such as Avoncliff and Dilton Marsh. In these instances, the guard releases only their local door with these new panels, so drivers do not release the doors at the stations with short platforms. This method of operation has now been retrofitted to North Downs and Oxfordshire services. Operations When built, these units were operated by the Thames Line and North Downs Line subdivisions of Network SouthEast. Their main destinations included fast-trains to Reading, Newbury and Oxford, with some services continuing beyond Oxford to Banbury and Stratford-upon-Avon, or along the Cotswold Line to Evesham, Worcester, Great Malvern and Hereford. Units are also used on the Reading to Gatwick Airport services along the North Downs Line. Many services operated by the 166 were branded as Turbo Express in the timetables. Following privatisation, the units passed to the Thames Trains franchise. In April 2004, operation of the Thames Trains franchise passed to the First Great Western Link, and subsequently to First Great Western. In 2012, First Great Western took delivery of five Class 180 Adelante units for Cotswold Line services, and three-car Sprinter units for Reading to Basingstoke Line services, allowing Class 165 and 166 units to be used entirely for Thames Valley services. In July 2017, the 166s began to transfer over to be based at St Philip's Marsh depot in Bristol, where they would then begin operation on the Severn Beach line to allow other services to be strengthened further west. Since September 2017, they have rapidly been introduced on other services such as the Weston-super-Mare to Filton Abbey Wood / Bristol Parkway service and the Cardiff Central to Taunton services. In January 2018, they began service on the Golden Valley Line and in February 2018, they