POLICE have warned graffiti taggers not to spend the lighter evenings risking their lives spraying on railway lines.
The vandals took a big gamble climbing on to train tracks to paint graffiti on Bremhill tunnel, between Cricklade and Purton.
There is no pavement on the side of the B4553 where the walls of the railway bridge have also been tagged.
The bridge is too narrow for two-way traffic to pass on it, but taggers have still stood at the side of the road to paint on the walls.
Network Rail said they were investigating the vandalism at the bridge and said people walking on the tracks were "playing with their lives."
A spokeswoman said: "Our maintenance crews fight a never-ending battle to remove graffiti, which in some cases appears almost as soon as it is cleared away.
"In addition to the unsightly disadvantages of graffiti, anyone trespassing on the tracks is literally playing with their lives.
"About 60 people each year are killed and hundreds more injured trespassing on the railways, either looking to commit acts of vandalism, taking short cuts messing around or playing chicken.
"Those who trespass not only put themselves at risk of disfigurement and death, but also endanger others.
"We are keen to work with the British Transport Police and train operating companies to explore partnership approaches to tackling graffiti in Swindon."
British Transport Police warned that trespassing on railway tracks is a crime that can see offenders taken to court or fined up to £1,000.
Transport officers warned youngsters to stay away from railway lines and said crimes on the rails, known as route crimes, were more prominent as the evenings become lighter.
Route crime officer for the British Transport Police, PC Clive Davies, said: "Trains reach high speeds and can travel almost silently.
"It can take up to two miles for trains to stop on full emergency braking, so if there are any obstructions and trespassers, there is very little action that the train driver can take to prevent the potentially severe consequences.
"With all these dangers I hope parents will urge children not to see the railway environment as a playground."
British Transport Police urged that anyone with information about crime on the railways contact them on 0800 405040 or call Crimestoppers anonymously on 0800 555 111.