A railway bridge over the Briggate River in Whittlesey is set to be replaced during the August bank holiday weekend.
The bridge is on the line between Ely and Peterborough and is used by up to five passenger trains an hour and twelve freight trains a day.
The existing timber decked bridge will be replaced with a stronger steel decked one.
Without the replacement a speed restriction would need to be imposed but Network Rail says that would result in delays to passengers and freight services.
Also the river will be kept open while the work takes place.
Passengers are advised to check before they travel as a rail replacement bus service will run from between March and Peterborough throughout the work.
Details are available at www.nationalrail.co.uk