The stark warning this week from Network Rail follows multiple incidents of walkers using the railway to get to the other side of the River Esk, at Sleights.
Members of the public are using a private road, where there is no public right of way, before reaching Thistle Grove Farm crossing.
This is a private level crossing which is for authorised users only – and they are given training on how to use it correctly.
People are using the crossing, then walking next to the track and over the bridge, which is known locally as Thistle Grove bridge.
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They are then trespassing on another private level crossing, Eskdale Gate No 2, before they reach a public footpath to Eskdaleside.
Network Rail is warning people that the upgraded railway bridge is not safe for members of the public to access.
The improvements carried out to the bridge last month are to help engineers when they maintain the railway and should be used by trained railway workers only.
Those who attempt to use the bridge, as well as the private level crossings in the area, to get to the public footpath towards Eskdaleside are trespassing on the railway.
Signs have been put up in the area to warn people to stay away from the tracks. Network Rail has also installed two cameras to deter trespassers and record anyone who ignores the warning signs.
Dawn Sweeting, Community Safety Manager for Network Rail, said: “People who are illegally using the railway bridge, intentionally or not, as part of their walking route seem to be completely oblivious to the dangers that they are putting themselves or their loved ones in.
“Trespassing on the railway is always dangerous and can have fatal or life changing consequences.
"You never know when the next train is coming, and everyone loses when you step on the tracks.”
Trains travel at high speeds and they cannot stop quickly or swerve out of the way.
If you see someone trespassing, call British Transport Police on 0800 40 50 40 or text 61016 to report it.
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