By Iain Docherty, Professor of Public Policy Governance at Glasgow University

Airport rail links intuitively seem like a good idea. Why wouldn’t we want to make it as easy as possible to whisk tourists and business people to the city centre to spend money and create jobs?

As ever though, the devil is in the detail. There are nowhere near enough of these inward business and tourist trips to justify the cost of this kind of expensive infrastructure.

To be economically justifiable, rail links need to capture a significant proportion of the people who travel to the airport either every week to fly for business, or every day to work there. Geography makes this difficult in Glasgow: a city centre link will not lure regular passengers who are focused in East Dunbartonshire, East Renfrewshire and the west and south of the city.

These issues are why building an airport rail link has long been a difficult policy and political challenge.

A new report suggests the latest iteration of the project – a tram-train using the heavy rail network to access the city centre – will actually cost the economy money. This is largely because train-trams will slow down other rail services.

But they would also use up capacity on the rail network and at Central Station that could otherwise be allocated to further improve the commuter rail services that carry many more passengers than an airport link ever will. Such improvements are essential.

Yet despite all of these complexities, some kind of fixed link to the airport remains attractive. Many other cities either already have or are building them. They are often seen as part of the standard ‘offer’ that large cities need to attract investors.

The question, therefore, is how to deliver an airport link that makes economic sense?

If we decide to build something linking the airport we should make it the right thing. Glasgow has changed since the first 1980s plans for GARL. We now have a corridor of investments, including the inner riverfront regeneration areas, the Queen Elizabeth hospital, and Braehead. A rapid transit route linking the airport and city via these developments would be an alternative worth investigating.

Iain Docherty is Professor of Public Policy Governance at Glasgow University.