Editing Chiltern Main Line (section)

===Rejuvenation===
[[File:165027 at Kings Sutton.jpg|thumb|right|Class 165 DMUs were introduced to the Chiltern Main Line by Network SouthEast]]

With the sectorisation of British Rail in the mid-1980s, operations south of Banbury fell under the control of [[Network SouthEast]] in 1986, under the ''Thames & Chiltern'' sub-sector; this was split later into two constituent parts. In 1987, a new station was opened at [[Haddenham & Thame Parkway railway station|Haddenham & Thame Parkway]]. Birmingham Snow Hill reopened in 1987, on a much smaller scale than the original, beneath a [[multi-storey car park]]; its tunnel was reinstated and new platforms added to the through lines at Moor Street, where the terminus was taken out of use. Leamington/Stratford services were diverted to Snow Hill.

The opening of the extension of the parallel [[M40 motorway]] from Oxford to Birmingham in 1991 spawned development in towns along the northern section of the route, notably Bicester, Banbury, Leamington Spa and Warwick. This generated additional patronage for train services in the corridor.<ref name="OM">{{cite news |title= 100-year-old rail station steams into the future |url= https://www.oxfordmail.co.uk/news/8247619.100-year-old-rail-station-steams-future/ |work=Oxford Mail |access-date=21 October 2021 |date=1 July 2010}}</ref>

Between 1988 and 1992, British Rail used the Chiltern Line as a test bed for [[total route modernisation]]; this included resignalling from Marylebone to Aynho Junction, and both Marylebone to Aylesbury routes, from the new Marylebone [[Integrated Electronic Control Centre|Integrated Control Centre]], with full [[Automatic Train Protection]] provided. The track was renewed and Marylebone was refurbished. Much of this work was funded by selling part of Marylebone for development, which meant that the station lost two of its platforms; the central cab road at Marylebone was removed and two replacement platforms inserted in its place.<ref name=Almostterminal/> 

New {{brc|165}} ''Turbo'' trains were introduced in 1991, replacing the ageing 1960s diesels.<ref name=Almostterminal/> These improved passenger comfort and enabled journey times to be reduced; frequencies were increased, with an hourly stopping service to/from High Wycombe and hourly semi-fast service to/from Banbury. In 1993, Marylebone-Banbury services were extended to Snow Hill, calling at Leamington Spa, Warwick, Solihull and Moor Street, initially on a two-hourly frequency; these were increased to hourly in the following year. In 1995, the [[Birmingham to Worcester via Kidderminster Line|Jewellery Line]] was reopened, to allow Worcester line services to be diverted from New Street to Snow Hill; this resulted in some of Chiltern's weekday peak-period services to be extended beyond Snow Hill, first to Stourbridge Junction and then to Kidderminster.<ref>{{cite book |last1=Boynton |first1=John |title=Main Line to Metro: Train and tram on the Great Western route: Birmingham Snow Hill–Wolverhampton |date=2001 |publisher=Mid England Books |isbn=978-0-9522248-9-1 |page=70}}</ref>