RAIL journey times from Inverness, Aberdeen and Dundee to the central belt could be cut if tracks were doubled and electrified, transport campaigners have said.
Transform Scotland says the country's rail network is in need of upgrading and has issued a list of key developments it says would bring cities closer together.
As well as calling for the electrification and doubling of rail lines, the group suggests a new direct rail link from Perth to Edinburgh, cutting up to 35 minutes off travel times from Inverness and Perth to the capital.
Spokesman Paul Tetlaw said the 71-minute journey time from Perth to Edinburgh is slower than the equivalent journey 100 years ago, when it took 65 minutes.
Mr Tetlaw said: "Scotland needs a rail revolution.
"Our campaign will build broad civic support for a planned programme of investment in the Scottish rail network over the next 15 years to bring all seven of Scotland's cities closer together with a safe, civilised and sustainable mode of transport and make Scotland's rail network fit for the 21st century.
"In doing so, we can reduce journey times, support travellers and commuters, create jobs, support the Scottish economy and reduce Scotland's carbon emissions."
Transform Scotland is an independent charity that advocates sustainable travel and has a membership of around 60 organisations.
The group's Inter-City Express campaign is supported by Rail Freight Group, Capital Rail Action Group, the Friends of the Far North Line and the Scottish Association for Public Transport.
Rail Freight Group spokesman David Spaven said: "The great thing about radically upgrading the rail infrastructure north of the central belt is that freight transport would benefit enormously, as well as passengers.
"With a fit-for-purpose Perth-Inverness railway, for example, we could increase the number of daily freight trains from two to as many as eight in each direction. That's the equivalent of taking more than 300 lorries off the A9 every day."
WWF Scotland director Lang Banks said: "Road transport is one of the biggest sources of carbon emissions in Scotland. If we're serious about meeting our climate change targets then we need to see a significant shift from road to rail and other forms of sustainable transport.
"It's clear to see that increased investment in rail would be good for Scotland's communities, our economy and the environment."
A Transport Scotland spokeswoman said a number of changes to improve peak-time travel to and from Aberdeen on weekdays will be implemented by ScotRail from May and its Aberdeen-Inverness Rail Improvements Project will reduce journey times and provide greater connectivity.
A spokeswoman said: "Direct infrastructure investment by the Scottish Government to reverse decades of neglect shows record levels of funding, with £8 billion committed over the next two years."