Officers found pieces of wood and concrete slabs had been dropped onto the track by vandals close to Dunfermline Town station, with the incident reported around 12:30pm on 25 March.
Three trains had then travelled over the objects, threatening a potential derailment.
Just a few hours later at 4:50pm, police received a further report of a wheelbarrow striking a train on the line close to Dunfermline.
British Transport Police said there had “luckily” been no damage to the train or injuries to people.
Officers are investigating both incidents in Dunfermline and are keen to stress the serious dangers of interfering with the railways.
In a separate incident on 27 March around 9am, the driver of an Inverness to Edinburgh service reported a near-miss of a dog-walker at a level crossing near Springfield.
The man was talking on his phone and absent-mindedly walked across the level crossing in front of a train.
Sergeant Derek Elder said: “These are all very dangerous incidents and I am thankful there weren’t more serious consequences.
“Trespassing in itself can pose grave danger to the reckless individuals involved. Railway lines are operational 24 hours a day and trespassing at any time of day can easily prove fatal.
“Throwing objects onto the tracks also puts both passengers and staff at significant risk, not to mention the thousands it can cost in repairs to trains and railway infrastructure.
“Likewise, not taking due care and attention at level crossings is of serious concern, and this man was lucky he wasn’t injured, or even worse killed.”