Rail services to London Paddington could be delayed by up to 45 minutes due to a broken-down freight train.
National Rail has warned the incident happened between Basingstoke and Reading, with routes between the stations affected, meaning services could also be cancelled or revised until 7pm on Wednesday.
It comes after motorists were warned of severe delays on a major road linking east London to Essex with tailbacks of up to six miles.
A stalled truck on the A13 before the North Circular at Beckton Roundabout closed two lanes, causing congestion to Wennington, past Barking, Dagenham and Rainham.
Motorists on the M25 near Heathrow were also warned of potential delays after earlier reports of a vehicle being driven the wrong way.
