Union leaders have ordered them to slow to to 20mph over automatic open crossings until the introduction of “appro-priate obstacle detection technology” and barriers.

The change follows the deaths of three elderly people at an unmanned level crossing at Halkirk, in Caithness. The car in which they were travelling was crushed by a sprinter train at an unmanned level crossing.

Keith Norman, general secre-tary of the Aslef union accused operator Network Rail of unwillingness to invest in ‘vital’ obstacle detection measures at level crossings.

He added: “By reducing speeds to 20mph over crossings, Aslef members can safeguard the health and safety of both train drivers and the travelling public.”

The union’s edict emerged as the British Transport Police said a bus driver was spotted driving through a red light at a rail level crossing with passengers on board on Monday.

A spokesman said that officers saw the bus at Cleghorn in South Lanarkshire during Operation Galley, which aims to cut down on dangerous driving at crossings. Two other drivers were also seen passing a red light at the same crossing during the day-long operation.

Inspector Stuart Wilson said: “Motorists at crossings across the country were stopped and issued with advice about the proper procedure when using level crossings on the rail network.

“This initiative was extremely well received by members of the public and rail staff, and rest assured Operation Galley will be repeated in the coming months.

“It is unfortunate that there are still those who think they can take a risk when approaching a level crossing, and in these cases we will prosecute them.”

A 56-year-old man will be the subject of a report to the procurator fiscal for not following the proper procedures at Charleston level crossing in Perthshire.

The police force said that at some crossings, including the one at Charleston, drivers are required to call the signal operators before and after they cross.

More than 20 British Transport Police officers were joined by members of Network Rail’s Community Safety team at sites including crossings at Kingsknowe, Whitelaw and Kirknewton in the Lothians, Gatehead in Ayrshire and Cambus and Blackgrange in Clackmannanshire.

Mark Henderson, Network Rail’s community safety manager for Scotland, said: “It’s disappointing that, despite all the recent publicity, people are still risking lives by ignoring red lights at level crossings.

“While it’s worrying that we continue to see such irresponsible, illegal behaviour, it was a good opportunity to speak to drivers and reassure them that level crossings are safe if used correctly.”

A notice of intended prosecution will be sent to the registered owners of the vehicles seen being driven illegally. The drivers could be charged with failing to obey a traffic sign under the Road Traffic Act, fined £60 and have points added to their driving licences.

Angus MacKay, his wife Margaret, both 81, from Inverness, died along with Mr MacKay’s brother Donald, 66, from Latheron, Caithness, when a train travelling from Inverness to Wick collided with the car in which they were travelling earlier this month.

The Rail Accident Investigation Branch has launched an inquiry into how the triple tragedy happened, which will also examine wider safety issues over automatic crossings.