The Scottish Government says the move will make railway policing more accountable but critics include trade unions and BTP officers.
68 billion midges in Scotland
Scotland has an estimated midge population of 68 billion, according to an expert on the often irritating blood-sucking insects.
Dr Alison Blackwell, who provides the Scottish Midge Forecast, has calculated the figure based on how many midges were found within a square metre area.
Her estimate focuses on inland areas in the Highlands and islands where the majority of the insects are found.
The population, she said, varies from year to year and is driven by the female midge population which is responsible for biting.
Dr Blackwell, who owns APS Biocontrol in Dundee, said: "The estimate is based on what we know about Scotland's habitat and population.
"What we've got is about 68 billion midges during the summer season, of which 21 billion will be female.
"We don't know what's going to happen to the midge population this year, it really depends on the weather.''
She said there can be as many as three waves of midges during the year, starting at various points in the summer.
Midges generally emerge in mid to late May, when the male non-biting insects arrive, before the blood-sucking females follow in June.
At this stage the males die off, leaving the females to do the damage for the remainder of the summer. They can remain an issue until September.
She said: "We usually get our first big catch the first week in June.
"It has been quite mild on the west coast and you've got a bit of humidity as well.
"The numbers should increase between now and the end of June.''
The number of midges also depends on how many generations of the insect there are, which is guided by factors such as a warm and wet summer.
She added: "You've got two generations in the summer time, but sometimes you get a third generation at the end of the summer, it really depends.
"You can't really stop them, they are part of the ecosystem.''
The Scottish Midge Forecast begins in mid-May and provides an insect annoyance scale of between one and five depending on the time of year and the number expected.
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