Two adjacent articles ("Dilapidated transport system costing Scottish economy billions" and "Climate committee calls for huge emission cuts by 2020", The Herald, December 2) linked the debate on how to persuade people to leave their cars at home and use more environmentally-friendly methods of mass transit instead.

Investing billions in our transport system is, as the first article points out, a given. The issue is where do we invest to make the dramatic environmental changes needed. Do we spend more and more on roads, like the extended M74 through Glasgow or the Aberdeen orbital? Or should we invest, as the Chamber of Commerce suggests, in a high-speed rail link from Scotland to London?

Anyone who ploughed through Sir Nicholas Stern's report to government on the likely impact of climate change in Britain in the next 50 years will certainly conclude that it makes grim reading. The most memorable line in his conclusion reads: "The cost of doing nothing to combat global warming will be the most expensive option of all." It is no surprise, then, that his committee considers the more far-reaching option of universal free public transport as an effective way of reducing our CO2 levels.

There is a growing belief that this is, in fact, the most appropriate way to repair our "dilapidated" transport network and, at the same time, combat greenhouse gases such as CO2. This option gives people a better option than using their car by offering free travel on publicly-owned buses, trains, trams and ferries.

It is felt increasingly that investing the hundreds of billions earmarked for more and more road projects in new buses, trains, trams and ferries would be much more likely to reduce our CO2 emissions and other pollutant levels.

In a debate at Holyrood in 2007, initiated by the Scottish Socialist Party, Tavish Scott, the then transport minister, put the cost of introducing free public transport in Scotland at £500m per annum. This sum, which now looks like chicken-feed alongside all the billions spent on bailing out five reckless banks, was calculated as the accumulation of all the income generated from fares that year.

I had to point out to Mr Scott that he had, in fact, got his sums wrong as the bill was probably nearer to £1bn as he had made no provision for the extra buses, trains, trams and ferries that would be needed to meet the increased demand. And increased demand there would certainly be, and very welcome, too.

The Belgian city of Hasselt introduced free public transport in 2002 with unqualified success. It reduced congestion, pollution and CO2 levels on the one hand, and successfully persuaded people to leave their cars at home on the other, witnessing a 960% increase in passenger numbers within the year.

Scotland needs to meet the twin challenges posed by our choking, gridlocked transport system and our international obligation to reduce CO2 levels by 80% by 2020. Providing free public transport rises to these challenges progressively instead of passing the buck and potentially disastrous consequences on to future generations.

Colin Fox, National Spokesman, Scottish Socialist Party, 8 Alloway Loan, Edinburgh.