A REGULAR dilemma for Scottish journalists covering General Elections post-1997 is remembering which aspects of government are devolved and which are reserved to Westminster.

In other words, what issues are relevant to Scots as they cast their votes on May 7.

This is particularly true of transport policy, the bulk of which is now controlled by ministers at Holyrood - or more often, in the hands of local authorities.

So if your gripe is with poor bus provision, ferry fares or cycling infrastructure, next month's ballot box is null and void.

But that does not mean the outcome of the UK General Election is irrelevant to Scotland when it comes to transport matters.

High-speed rail, regional airports' access to a UK hub, and a demanded shake-up of rail franchising were among the topics on the agenda at a recent hustings in Glasgow.

Moreover, Westminster will decide where to locate the proposed UK spaceport - an outcome Scotland has a disproportionate interest given that four of the six shortlisted sites are found north of the Border.

The Maritime and Coastguard Agency, also reserved, has undergone reforms in the past five years which saw both the Forth and Clyde Coastguard stations closed - a process which MPs sitting on the Transport Select Committee said was "rushed and poorly planned".

Westminster is also responsible for setting the driving test, which the Institute of Advanced Motorists recently said fails to prepare learners for country roads - a particular worry for Scotland where the rural north-east and Borders have among the highest incidence of road deaths and serious injuries than anywhere in the UK.

So what differentiates the parties on transport?

Take HS2. Earlier this week Ed Milliband said Labour "absolutely supports" extending the high-speed rail link as far as Leeds despite previous comments by Shadow Chancellor Ed Balls questioning whether HS2 was "the best way to spend £50bn".

The Conservatives also back the move, while Deputy Prime Minister and LibDem leader Nick Clegg said last month that it would "finally address the North-South divide".

For Scots commuters it would shave around an hour off journeys from Scotland to London - but not until 2032.

The SNP would like something more ambitious: high-speed rail all the way from the Central Belt of Scotland to London, with concurrent construction projects building north to south and south to north, and eventually linking up.

So-called HS3 would cost the Scottish Government an estimated £10 billion.

While the other parties have made no concrete commitments, a Scotland extension won the backing of the Scottish Labour and Conservative panellists at the recent Glasgow transport hustings - though on the provision "if it happens, it must come to Scotland".

By contrast, the LibDem candidate said party policy would stop it south of the Border in favour of investment in northern Scotland's rail infrastructure.

Another major transport project with implications for Scotland is the expansion of either Heathrow or Gatwick, which - both airports insist - would boost connectivity from Scotland to London after years of dwindling services.

The Conservatives, Labour and the SNP all back extra runways in the south-east; the LibDems and Greens have vetoed extra runways for either airport.

Transport may not be a deal-breaker for most Scottish voters, but it isn't irrelevant either.