Young people have been warned to stay away from railway lines -- to prevent them injuring themselves and others.
Chiltern Railways, which operates trains through the county, has appealed to children and youths not to trespass on lines or at stations.
The calls have been backed by the company that owns the track, Network Rail
The train operator said Health and Safety Executive figures showed 52 per cent of train incidents were due to vandalism.
The placing of objects on tracks posed the most significant risk, leading to derailments and in some cases train collisions.
Steve Murphy, managing director of Chiltern Railways, said: "Parents and the local community should be extra vigilant this half-term.
"The cost to industry is immense in terms of service delays and damage to infrastructure but more disturbing is the risk to life."
Anybody who sees anything suspicious on the railway is asked to call the National Railway Crime Hotline on 0800 405040.
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