Trains running between Essex and London are set to be disrupted while works on a faulty track take place.
Network Rail will be carrying out emergency work to replace the track between Chadwell Heath and Shenfield this Sunday.
The affected rail is part of the track layout that allows trains to switch lines just outside Gidea Park station.
If the work was not carried out this weekend, the speed restriction could have to be lowered to 5mph, or the line might have to be blocked entirely at short notice.
This would mean unplanned disruption that could cause more severe delays to passengers over a longer period.
How will services be affected this Sunday
Greater Anglia
There will be no train services between London Liverpool Street and Shenfield.
Buses will operate between Newbury Park Tube station (central line) and Shenfield/Ingatestone.
Passengers travelling on the Southend Victoria and Southminster line should change at Shenfield.
Passengers travelling on the line to and from Colchester and Clacton-on-Sea should change at Ingatestone.
Ticket acceptance on the Central Line is in place with TfL.
Vital, pre-planned engineering work means that buses also replace trains between Colchester and Ipswich and Colchester and Harwich Town on both Saturday and Sunday.
On c2c, buses replace trains from Leigh-on-Sea to Shoeburyness on Sunday.
Elizabeth line
Buses will replace trains between Chadwell Heath and Shenfield, and there will be a reduced service of four trains per hour between Seven Kings and Chadwell Heath.
Other Elizabeth line services are not affected.
Passengers are advised to check the details of their specific journey before they travel at greateranglia.co.uk / nationalrail.co.uk / tfl.gov.uk
Share