New figures show the number of trains judged to be overcrowded on the ScotRail network has quadrupled over the past five years.
The Edinburgh-Glasgow service accounted for more than a quarter of the total number of overcrowded trains, with peak periods in the morning and afternoon proving to be the most packed.
In a typical week, passengers would have expected to stand for more than ten minutes on 34 services last summer, compared with just eight in 2006, according to the figures from Transport Scotland.
The overcrowding on the Edinburgh Waverley-Glasgow Queen Street trains at rush hour comes despite ScotRail’s policy of hiking peak prices to £19.80 for a return, compared to £11.40 at off-peak times.
Passenger Focus Scotland, the rail watchdog, said the figures show a growing problem of insufficient capacity.
Robert Samson, the Passenger Focus manager for Scotland, said: “The introduction of the new 380 [trains] will have improved the ability of passengers to get a seat.
“The onus is on the Scottish Government, Network Rail and ScotRail, who know where the capacity issues are, to plan for services to make sure people are able to get a seat.”
The worst overcrowding was on the Strathclyde network, which accounts for nearly two-thirds of train journeys in Scotland, with some trains having in excess of 100 more passengers than seats available on some services.
Around 78 million people travel every year with ScotRail, which accounts for 95 per cent of passenger services in Scotland since parent company First Group was awarded the contract to run services in 2004.
Passengers face another six per cent fare hike from next week following seven years in which prices have increased above the rate of inflation.
Edinburgh-Glasgow services are due to benefit from electrification of the line as part of a £1 billion investment in rail services, which is expected to increase capacity.
A ScotRail spokesman said: “We run more than 2300 servoces a day, with our fleet deployed in the most effective way possible to meet anticipated demand.
“Passenger numbers are monitored regularly and we spend a great deal of time planning train movements. But there will be occasions when there is sudden demand for a particular service.”