Regular trains between Birmingham Moor Street, Stourbridge Junction and Kidderminster are operated by West Midlands Trains as part of its "Snow Hill route" service. Chiltern Railways operates two parliamentary train services:  On certain Bank Holiday Mondays, services are extended from Aylesbury to the Buckinghamshire Railway Heritage Centre facilities at , a short way north of . However, this did not happen in 2019 and their future is uncertain. The link will continue to be used by freight services to Calvert. Since winning the franchise, Chiltern has introduced "Route: High Wycombe" tickets for the Chiltern route between Birmingham and London that are considerably cheaper than "Route: Any Permitted" tickets, valid on the faster Avanti West Coast service to London Euston as well a number of other operators and routes. Chiltern offers only Standard Class, not Standard and First Class as on Avanti services. However, Chiltern does offer a premium economy "Business Zone" carriage on a small number of peak-time trains between Birmingham or Oxford and London. Passengers pay an upgrade fee to sit in a larger first-class-style seat; and formerly, this upgrade came with complimentary refreshments but, since May 2017, refreshment services have been cut on all Chiltern Railways services, meaning the "Business Zone" no longer comes with complimentary refreshments. Chiltern was considered one of the best operators in Britain, with Public Performance Measure (PPM) regularly over 90%, until the introduction of changes in November 2015 and infrastructure issues saw punctuality fall to 86% in December 2015. Chiltern's PPM is measured on stricter conditions than its long-distance rivals, such as Avanti West Coast, as Chiltern has a 5-minute window for performance while others have a 10-minute window. Performance figures published by Network Rail rate Chiltern Railways sixth in train operating companies in the UK at 89.4% (PPM – period 9) and 94.3% (MAA) for the year to 12 December 2015. A new timetable introduced in September 2011, combined with significant disruption caused by engineering work, caused a negative reaction from customers. A petition to have the service reviewed was started, and articles describing the disrupted journeys of commuters appeared in the local press. A new timetable introduced in December 2012 also met with frustration and opposition from some customers, particularly those using Saunderton and Princes Risborough stations. Evergreen is the name given by Chiltern to the major infrastructure works that the company has committed to over the 20-year duration of its franchise to improve routes and services.