There's a bit of detail about it in a TfL powerpoint presentation
titled "11 May 2005 - Minutes (Appendix 4 - Transport for London)" on
this page:
http://www.croydon.gov.uk/counciland...981/aww?a=5441
- it's a 2.8MB download,
Looks like the point of it was to improve reliability between Norwood
junction and Croydon.