'There needs to be a recognition that the Scottish rail network is essentially unfit for purpose north of Perth at present.' That damning - but accurate - verdict came from the Scottish Chambers of Commerce in their response to the Scottish Government's Rail 2014 consultation.

Upgrading of the railway network north of the Central Belt has been severely neglected for 40 years, a period during which there has been unprecedented road investment, such as the complete rebuilding of the A9 from Perth to Inverness in the 1970s and 1980s. The last upgrade of the parallel 118-mile Highland Main Line was in the mid-1970s, when 35 miles of track were redoubled and three new crossing loops installed.

Ironically, there has been disinvestment in the Highland Main Line since then, with three crossing loops removed, creating even longer single-track sections and reducing capacity and flexibility.

So what does this mean for rail freight, the safe and sustainable alternative to road haulage? Firstly, there is a stop-start journey from rail hubs in Central Scotland to various terminals in Inverness and beyond. In contrast, the road haulier can contemplate an uninterrupted journey over roads which are entirely dual-lane or dual-carriageway.

The second infrastructure barrier is the highly-variable length of crossing loops - not a major problem for relatively short passenger trains, but hugely significant for freight. Rail freight can best compete with long trains of multiple loads hauled by a single locomotive. Yet rail's competitive opportunity is severely hamstrung between Perth and Inverness, with the shortest of the nine crossing loops being just 265 metres in length compared to the longest of 505m.

How does this impact on key freight flows, particularly in new markets which rail has developed over the last two decades? The daily Stobart/Tesco train from Mossend to Inverness is limited to 20 containers, yet the Class 66 locomotive hauling the train could handle up to 28 containers (lorry load equivalents) if loop lengths were consistently longer (530 metres+). That would have an enormous impact on rail's ability to win traffic from road haulage.

The last, but certainly not least, infrastructure constraint along the Highland Main Line is the limited 'loading gauge', in other words the capability of square-profile tall containers to pass through arched tunnels and overbridges. Scotland's rail network as a whole is a patchwork of six different loading gauge clearance categories, making for complex choices as to what width and height of container can be safely accommodated on different types of rail wagon. In contrast, the road haulier simply utilises a standard tractor and trailer combination, since height constraints have long been eliminated from the trunk road network, courtesy of the taxpayer.

These gross disparities between rail and road network capacity and capability are a key reason why the Rail Freight Group is supporting the Inter-City Express (ICE) campaign led by Transform Scotland, the sustainable transport alliance, to push for a fit-for-purpose network north of the Central Belt. ICE is arguing for electrification, extension of double track and more, longer crossing loops on the routes linking Glasgow and Edinburgh with Aberdeen, Inverness and Elgin.

The Scottish Government's intentions for upgrading freight capacity and capability on the Highland Main Line remain unclear - all we know is that 'more efficient freight operations' were promised for the period 2014 to 2019.

With a properly-upgraded Perth-Inverness railway we could increase the number of daily freight trains from two to as many as eight in each direction, carrying a wide range of commodities. It would be the equivalent of taking more than 300 lorries off the A9 every day. A government really committed to sustainable economic development - and road safety - would regard this as a golden opportunity.