IT was introduced to make ferry travel cheaper and boost visitor numbers to Scotland's remotest islands.

But now the architect of the Road Equivalent Tariff Scheme is calling for it to be overhauled amid fears its introduction has left many islands' infrastructure struggling to cope with the rise in visitors.

RET bases fares on the cost of travelling the equivalent distance by road and was introduced on the Western Isles, Coll and Tiree in October 2008, cutting fares by up to 55%.

It was extended to Islay, Colonsay and Gigha in October 2012, to Arran in October 2014 and now covers every route.

Across the network, car traffic has increased by just over 25%, which is causing severe problems as islanders struggle to book ferries and increased traffic contends with many single-track roads.

Now transport expert Roy Pedersen, who spent 30 years in Highlands and Islands development and devised the scheme in the 1970s, now says it should be reformed with some vehicles exempt from receiving it altogether.

He said: "I was the original architect of RET and its application has generated additional traffic which has taxed the capacity of many existing routes.

"RET is a very blunt instrument and rather out of tune with modern yield management practices.

"In a number of cases the fare subsidy to tourists travelling on Clyde and Hebrides services is greater than the spend of tourists on the island communities visited where accommodation is in many cases already at, or beyond, capacity.

"Policies that are worth considering for addressing this issue are higher fares on peak tourist services, no RET on camper vans whose users contribute little to island economies and certainly no RET on commercial vehicles".

Last year, CalMac carried more than five million passengers, nearly 1.5 million cars, some 80,000 coaches, and just under one million metres of commercial traffic.

The number of motorhomes travelling to the Western Isles has risen over the past decade, with nearly 2,000 heading to Harris alone.

The rise has led to calls that motorhome users should face a levy on ferries and comes after a summer of disruption across the ferry network due to breakdowns, with the average age of vessels plying routes now being 22 years.

Tourism bosses on the Outer Hebrides have warned the disruption has cost them millions of pounds this year and how the network is run in the future is currently under scrutiny, with many islanders demanding more vessels with increased capacity.

Mr Pedersen lodged proposals to MSP's that would see the current model of serving island communities ripped up and instead will be based on the Norwegian system of smaller ferries covering shorter routes.

The move aims to increase capacity with more ferries and in some cases journeys being broken up using islands as ‘land bridges’ to reduce journey times.

It would see islanders in the Outer Hebrides able to do business on the mainland in a day and return home without an overnight stay.

According to the expert behind it, it would also help repopulate islands as crew would live on the islands they serve rather than on board and staffing costs would be reduced.

Perhaps crucially, it would also dramatically reduce the annual subsidy paid to ferry operator Caledonian MacBrayne to run the service.

Under his plan, a new fleet of around 10 smaller, more efficient ferries would be built with the total bill of around £280 million. Upgrades to the ports they would serve will cost another £20 million.

Ferries would be crewed by a staff of around 12 to 14 as opposed to the 30-plus currently used which would allow them to work shifts as at other operators and in Norway and enable more ferries to run during the day and extend the timetable with services starting earlier and finishing later.

Staff would also live in the communities they serve which, it is argued, would help boost the populations of remote island communities as the smaller ferries would be based in the island ports and not on the mainland.

So far this year five ships on Clyde and Hebridean services have been out of service.

Islay, Harris and Uist have all been hit by disruption, when the Hebridean Isles - built in 1985 and one of two ferries that normally serve Islay - was withdrawn to work on the Tarbert and Lochmaddy routes.

Newer ships, such as the MV Clansman, which services the Outer Hebrides from Oban, were among those out of action. The knock-on effect of vessels being redeployed proved to be a severe test for the 32 ferries that serve 51 ports on 49 routes.

Between January and the end of July this year, 2,326 out of 79,203 CalMac scheduled sailings were cancelled. Of these, 327 were for mechanical reasons with the rest mostly due to bad weather.

Outer Hebrides Tourism (OHT) said ministers must address CalMac's ageing fleet and its inability to move beyond the "knife-edge on which it sits" for service reliability.

Among its other complaints are that two new ferries were delayed "with nothing else in a build pipeline".

Minister for Energy, Connectivity and the Islands, Paul Wheelhouse, said: “Road Equivalent Tariff (RET) has delivered significant ferry fare reductions to the Clyde and Hebrides, leading to a welcome boost in carryings which supports our island and remote communities. Transport Scotland has recently commissioned a full network-wide evaluation of RET which will examine its successes but also any negative impacts in terms of creating capacity constraints. The evaluation is due to report at the end of 2019 and the findings will be considered in due course, but, in the interim, I and Transport Scotland continue to engage with stakeholders on the impact of passenger growth on services."