Fencing is starting to be installed before work on the Levenmouth rail link launches.
19 kilometres of fencing is being erected so that forthcoming work to reinstate the branch line can be carried out safely.
It's also to stop members of the public coming into contact with the plant and machinery carrying out the work.
The fencing being installed will extend along the full length of the route to secure the boundaries of the rail corridor, but existing pathways and crossing points will be maintained while early phases of work take place.
Network Rail says it's also sectioning off some bridges on the route between Cameron Bridge and Thornton junction to carry out work.
The organisation says that due to the nature of the activity on the bridges, it's important that the area is secured to maintain public safety.
As part of preparatory work, vegetation has been cleared along the five-mile corridor and the removal of redundant and life-expired railway equipment from the former line.
Treatment of invasive plant species has taken place, structures inspected and trial holes have been drilled along the full length of the route to check ground conditions and test for contamination.
Joe Mulvenna, Network Rail project manager for the Levenmouth Rail link said: "While we understand that over the years, the disused railway has been accessed by people exercising and enjoying the river, as well as crossing on well-used paths between communities, that will not be the case for much longer.
"The whole corridor between Thornton and Leven will soon become a major construction site and while we will maintain some limited access on paths across the railway corridor during the early phases of work, in general we are asking people to find alternative walking routes.
"The scale of the work that will be involved in the project means that in the short-term there will be some disruption for the area, but It is an exciting development that has the potential to transform life for local people and the communities it will serve."
It comes after the Policy and Coordination Committee at Fife Council approved essential works to be carried out on the Leven Rail Bridge.
David Alexander, the SNP co-leader at the local authority, said: "Our capital plan originally included some £2.5m to upgrade the Bawbee Bridge, as it’s known locally.
"That was based on much simpler work on the bridge before we knew there was going to be a rail link with live electrified lines and before we knew where the stations were going to be.
"Now it’s a completely different project and, given the scale of the work, we’re also building in costs to create a diversion to keep communities connected.
"So, though costs have risen, this is because of the positive and exciting development now happening in Levenmouth.
"We’ve been working with Transport Scotland and Network Rail since the rail link was announced, to make sure the works would be aligned.
"We’ve agreed that these expert partners will incorporate the bridge replacement into their programme, managing the construction work as part of the overall development.
"It will all run as one project and we’re all determined to get these trains running on time!"
David Ross, the Labour co-leader at the council, said: "I agree that it’s vital that we go ahead with this work and this is the right solution.
"We want to reassure people about the additional funding for this work.
"To be clear, we will not be using any of the budget set aside for Levenmouth regeneration work.
"Nor do we intend to drop plans for other critical works around Fife.
"We have £10m allocated in the Capital Plan for bridge works, and we hold a capital contingencies budget, so we know we can cover the costs and we’re approving these plans now to get the Leven bridge works moving.
"Given the critical timescales involved in the national project, it must be the priority.
"However, we’re still committed to other bridge replacements and improvements that had been planned, such as the Cowdenbeath railway bridge.
"We’re actively looking for more national funding to help cover the costs in Leven so that we don’t have to take the money from our capital budget.
"We’re bidding for £6.35m through the UK Government’s Levelling Up Fund and exploring funding opportunities from Sustrans.
"And, because capital costs are rising across the board due to supply chain issues and material costs, we already know that we’ve got to review the whole capital plan.
"This will give councillors an opportunity to prioritise all our planned work, not just the bridge works, and decide what’s now affordable in the same timeframe."