Fischer has had a 52-year obsession with railways, ever since his father started taking him, at age 13, to Boree Creek station in the south-west of NSW to meet the rail motor on Monday morning to pick up the previous day's newspapers. Later, as transport officer for the 1st Battalion of the Royal Australian Regiment, he was responsible for organising the troop trains. ''Not an experience I want to relive, despite my love of rail,'' he jokes. Through a lifetime in politics - as a Country Party MP in the NSW Parliament, a National Party MP and leader in the Federal Parliament and, finally, as deputy prime minister to John Howard - he was Australia's most determined booster of railways. It has culminated in a new book, Trains Unlimited in the 21st Century, a sweeping study of railways around the world that was launched late last month. It is his second ode to rail; the first, Transcontinental Train Odyssey: the Ghan, the Khyber, the Globe, was published in 2004. Fischer is the genuine article - a trainspotter. There is a difference. The rail enthusiast, such as this writer, loves trains for their superior environmental qualities, their comfort over planes and buses, for the convenience of going from the heart of one city to another, for the way that rail lines always seem to traverse the most picturesque landscape in any country (much more so than motorways) and for the social interaction you have with locals and other foreign travellers.

But for the trainspotter, it's all that and much more. Fischer loves the intricacies of the train and the infrastructure itself: the class and power of the locomotive, the gauges and bogies (basically the undercarriage of a rail car), the steel-jaw clasps that couple the carriages together, the height of the tunnels and bridges, the depth of the dives. He gets as excited by the sight of a double-stack container freight train as he does by the sleek visage of the 350km/h TGV passenger trains that whoosh through France. He can recognise in an instant the sound of a 62 Class Garratt loco from a 30-year-old recording. But for all the romance, even idiosyncrasy, of this passion, Fischer's book is less nostalgia and more manifesto. It is serious analysis and a masterplan for the revival of passenger and freight rail transport around the world. And it comes at a critical moment because, for the first time, the Australian government - with support from the opposition and the Greens - is beginning real work on a high-speed train network that would link Brisbane and Melbourne, via Sydney and Canberra. A federal government report released last week estimated the cost at between $61 billion and $108 billion. When Fischer ends his term as ambassador in February - he has taken leave from the Foreign Affairs Department to promote the book, with part of the proceeds going to humanitarian and rail heritage charities - he will devote much of his time to realising the project. ''This is make or break time for high-speed rail in this country,'' he says. The Sydney-Melbourne corridor is the fourth-busiest air route in the world and Fischer says that, using an 822-kilometre route via the Southern Highlands-Goulburn, Canberra, Tumut, Albury-Wodonga and Tullamarine Airport, passengers could go from one city centre to another in less than three hours. A line built to take speeds of up to 330km/h could mean trains would travel at an average speed of 282km/h, well within practice for European and Asian fast trains.

''You know the Japanese started running high-speed bullet trains in 1964 and there have been zero - I repeat, zero - fatalities,'' he says. But Fischer had limited success promoting rail during his five years at the highest levels of government, unable to convince his Cabinet colleagues, other than on the construction of the single-track Adelaide-Darwin line, and even that was ''touch and go''. When the Howard government sold Sydney Airport and got an unexpected $1 billion, Fischer wanted to use it to begin high-speed rail between Sydney and Canberra. But he says the then head of the Department of Prime Minister and Cabinet, Max Moore-Wilton, who had previously run the NSW Roads and Traffic Authority, sunk the plan. ''My old friend Max the axe,'' Fischer says. ''A very competent public servant, a good man, but he had been a very powerful roads boss. The 'Max 101' tactic was to torpedo with inflated cost estimates and undermine the case for high-speed rail.'' Moore-Wilton recalls the case clearly but says the plan from Fischer, whom he describes as a ''living national treasure'', did not persuade the Bureau of Transport Economics.

''The numbers were very clear,'' he says. ''The capital costs outweighed the substantial economic benefit.'' It was this economic rationalism - this dogma that insists every government investment be revenue neutral or turn a profit, no matter what its broader social, economic, safety or environmental value - that Fischer believes has influenced all governments - state and federal, Coalition and Labor - for at least 20 years, ignoring the real costs of road and air transport. ''Because of greenhouse emissions,'' he says (indicating he is no climate change denier), ''and with fossil fuels running down, the 21st century will be the new era of rail. Look at the speed and efficiencies they're getting now in Spain, France, London to Paris, London to Brussels. This is not an old-fashioned technology.'' Without a serious expansion of freight and passenger rail, Fischer argues Australia will need to build a second Sydney airport - at an estimated cost of $15 billion, according to a 2010 Infrastructure Partnerships Australia report - a 10-lane Hume Highway from Sydney to Melbourne and a 12-lane M3 between Sydney and Newcastle. He also says that within six years of opening, the Adelaide-Darwin line had increased its freight traffic five-fold.

Not only is Fischer pushing for intercity fast trains, he wants to upgrade existing lines and reduce travel times on country services in NSW, Victoria and Queensland so they can reach their potential of about 160km/h. Sydney-Lithgow could become a 75-minute journey with a new track via Warragamba; Victoria's regional lines could be improved for quicker commute times to Melbourne; the Gold Coast light rail, currently under construction, could run to the NSW border and connect with a boutique commuter line through the Tweed Heads-Murwillumbah-Lismore hinterland. But Fischer's plans also go beyond just Australia. A couple of months ago in Rome, the ambassador from Benin called on him, ostensibly about a Vatican issue. When matters papal concluded, the envoy of the small west African country quizzed Fischer about how rebuilding the colonial-era freight and passenger lines could boost its economy. Fischer wants to realise Cecil Rhodes's dream of a north-south line between Cairo in Egypt and Cape Town in South Africa - ''unlikely in my lifetime,'' he says - but thinks an east-west line along the Mediterranean coast, linking Morocco with Egypt, via Algeria, Tunisia and Libya, is more realistic.

With its remaining rail systems being largely antique, Africa also sums up for Fischer the emotional, almost psychic, power of the railways. ''There is just a soothing clickety-clack,'' he writes in Trains Unlimited, ''although this is no longer the case in Europe and North America, where the railways are all welded, but is still happily the case in many parts of Africa.'' Fischer's travels, official and personal, have taken him to 72 countries, 60 of which have extensive rail systems. One weekend a month, since taking up his post as ambassador to the Holy See in 2009, Fischer has escaped Rome to ride the rails, often deep into eastern Europe and as far as Poland. In Vietnam, where he served during the war, he has made the epic Hanoi-Saigon trip aboard the Reunification Express. But the mother of all rail journeys remains unconquered - Beijing to Moscow, via Mongolia and Siberia. When I mention that my wife and I are doing the trip in September, he smiles and says: ''You bastard. You beat me to it. Email me some pictures - of the train.''