Train services across east slowed down to prevent line damage
Speed restrictions have been imposed on stretches of railway across eastern England because of high temperatures.
Network Rail said rails and overhead lines in direct sunlight could reach temperatures 20C higher than surrounding air.
Trains will be slowed down to prevent damage and this will have an impact on network services, a spokesman said.
The restrictions will involve train services in Hertfordshire, Essex, Suffolk, Norfolk and Cambridgeshire.
"They will be in place until 20:30 BST but I cannot give details of where the restrictions will be," the spokesman said.
Train services operating between London Liverpool Street, Cambridge, Colchester, Ipswich, Norwich and Southend Victoria will be subject to some alterations and cancellations.
"Customers are advised to check for travel updates, using websites, Journey Planner and live departure boards for any alterations," he said.
"We appreciate that passengers don't want longer journeys in hot weather however we have put speed restrictions also to prevent damage."