By Tom Symonds
Transport correspondent, BBC News
Across the UK the demand for travel is now huge
More than a decade ago, when the Conservatives were last in power, running Britain's tangled transport network was much simpler.
The challenges were fairly obvious. How do you keep the traffic and the trains, and therefore the economy, moving smoothly?
Going even further back, the answer to that question was "predict and provide" - work out how many people were going to want to travel and then build enough roads and railways to cater for them.
By the early 90s, the Conservatives had moved on to a variation of that theme, their Roads for Prosperity policy - building more roads to cater for a "car-owning democracy" in which driving was already getting cheaper and car ownership was soaring.
Forcing people out of their cars often means big government curtailing freedoms... not natural Conservative territory
The party's rail privatisation envisaged the managed decline of rail travel. Aviation pretty much looked after itself.
How things have changed, not least because devolution has seen responsibility for most aspects of transport policy placed into the hands of politicians in Holyrood, Cardiff and Stormont.
Carrots and sticks
Across the UK the demand for travel is now huge, by train, plane and automobile.
Secondly, the impact on the environment is central to the challenge.
Yes, the Tories had to contend with Swampy and friends, but the need to cut carbon emissions now runs alongside and equal to the need to cater for growth.
There is more. What now appears to be a long-term rise in fuel prices adds extra policy pressure.
Swampy (Daniel Hooper) dogged Tory transport schemes in the 90s
In many ways the Conservatives have always faced a greater challenge than Labour over transport.
Managing the pressure on networks and the environment, experts say, inevitably involves carrots and sticks - encouraging less car use by improving public transport (carrot) and forcing people out of their cars by making them pay more to drive (stick).
The trouble is that better public transport often costs more public money, raising the old debate over tax-and-spend policies.
And forcing people out of their cars often means big government curtailing freedoms. Again, not natural Conservative territory.
But all of the historic sharp edges are softening.
David Cameron's party is now ready to take on big business for environmental reasons by opposing - at least for the time being - a third runway at Heathrow.
In a recent speech Mr Cameron said he was increasingly of the view that the economic case for a bigger Heathrow was flawed.
He said: "I think the whole country can agree that the most important priority for Heathrow is making it better, not bigger - and yet Gordon Brown is pig-headedly pursuing a third runway just to try and prove a political point.
"What a ridiculous way to plan for the future."
Some aviation sources said this was just political positioning - the decision will be taken long before the Conservatives can hope to gain office, and they won't reverse the expansion once there.
There are similar paradoxes in the debate about cutting traffic congestion. It is seriously difficult to remove traffic from the roads and Labour has completely failed.
Tories back local congestion charges rather than a national scheme
The most radical response to the problem is congestion charging. On the face of it this is a perfect right-of-centre solution to a social problem.
You put a price on road space and create a sort of market where drivers work out how much they're prepared to spend.
But it is a tax, and the Tories aren't terribly comfortable with the cameras, databases and punishment systems needed to make it work.
So another carefully worded policy has developed.
We're in favour of local congestion charges rather than a national scheme, they say. But not if it is unpopular locally.
And therein lies the problem. Congestion charges are pretty much always unpopular locally, unless drivers are offered something as an alternative.
In other areas the natural urge of the party to turn to the private sector remains intact.
The M6 Toll which charges drivers to pay for its construction is seen as a success to be repeated; after all it was given the green light under a Conservative government.
And on the railways David Cameron's transport team has also repeatedly criticised the government for "micro-managing" from Whitehall rather than allowing the big rail operators the freedom to develop better services on their own terms.
Another theme is to encourage technological innovation to solve transport or environmental problems.
Will a PM Cameron insist that Britain gets on its bike?
David Cameron has set his party a tough target to reduce average car emissions by 2022.
The government wants to do the same, but two years earlier.
He would achieve this by what the Tories call "a well thought out system" - presumably of taxation, to encourage drivers to buy greener cars.
The Tories appear keener than Labour on the idea of building new fast rail lines linking Scotland and the north with London and the south, by promising a feasibility study.
However, Transport Secretary Ruth Kelly has recently asked Network Rail to conduct a feasibility study of its own.
In so many areas the two main parties are close together on transport issues, struggling to win the centre ground - just like two drivers jostling for the same lane of a crowded motorway.