With the exception of the "hell on wheels" of the Edinburgh trams project, there cannot be another infrastructure scheme in recent Scottish history which has been engulfed by as many false starts, turmoil and bickering as attempts to construct a rail link to Glasgow Airport.

And at least Edinburgh has something to show for its turmoil. It is now more than eight years since the Scottish Parliament passed the airport rail link Bill on November 29 2006, but the debate over what to build, where to build it and how to build it is still rumbling on - reignited days ago by the revelations of a long-awaited feasibility study into a proposed tram-train hybrid.

The scheme is by no means dead in the water, but on current projections it seems unlikely holidaymakers arriving at Glasgow Airport will be whisked into the city by tram any earlier than 2025.

Glasgow Central's platforms are simply too crowded, and will be for the foreseeable future.

Luckily for the airport bosses, business groups and councillors lobbying to press ahead with the project, they can look south of the Border for inspiration - and reassurance.

The UK's first ever tram-train hybrid is scheduled to start rolling in 2016 between Sheffield and Rotherham for a two-year pilot. What happens there will reveal much about what is possible here in terms of engineering and technology. It will also provide us with a "tool kit" - to quote this week's feasibility study - on how to replicate the infrastructure in other urban settings.

I would be reluctant to be too harsh on the prospects for Glasgow's tram-train until we see how England's pilot unfolds - though if it spirals into an Edinburgh tram-style disaster, you can guarantee the proposal will be quietly shelved.

So what are the obstacles? The impact on other passengers needs to be resolved. Although the authors of the report question the business case for the tram linking up with the heavy rail line at Paisley Gilmour Street, if that remains the plan then there will be clashes with existing rail services that require "significant timetable alterations and extended journey times for other passengers". Accommodating a tram-train service onto the line every 15 minutes will hit rush-hour commuters worst of all, adding to the controversy.

Then there is the issue of where to park the tram-trains once they arrive at Glasgow Central.

"An analysis of peak hour platforming at Glasgow Central has demonstrated that there is very little spare capacity available currently, and that it will be difficult to find platform space for four extra Tram-Train services each hour," says the feasibility study. It adds that sufficient capacity "could be a considerable time away, potentially ten years."

The drawbacks do not strengthen the case to resurrect a Garl-like heavy rail scheme, however.

Aecom, the consultants who last year recommended switching to the tram-train option, estimated it would cost £92 million compared to £207m to revive a heavy rail route. Not to mention the entirely toxic prospect of taxpayers buying back land they only recently sold back at a loss of £1.8m.

We might not be seeing light at the end of the tunnel yet - but it is not the end of the line either.