This is a very conservative Government. If there was any doubt about the caution of John Key's Cabinet it has been dispelled by its decision on the driving age.

Last year its transport officials floated the possibility of raising the age from 15 to 16 or 17 with restrictions until age 18. In January the Herald canvassed its readers on the subject.

The vast majority, 80 per cent of a Nielsen survey of 2300 people, thought the age should be at least 18. A few, 6.5 per cent, thought it should be 20. The Government's decision: 16.

Politics, like driving a car, is a matter of moving at the right speed. Governments can come to grief when they move too fast for the country's comfort or, like slow drivers, frustrate normal progress.

New Zealanders have known for many years that the right to drive at 15, an artefact of a largely rural society, was out of line with modern conditions. In most states of Australia the age is 17 and in Victoria, 18.

In the United Kingdom it is 17, South Africa 18. New Zealand roads are much better and busier now, and cars faster, than they were when 15-year-olds were awarded licences.

A road safety discussion paper issued by the Transport Agency last year reported that the human brain's capacity to assess risk and control impulse is not fully developed until people are in their 20s.

Drivers aged 15 to 24 made up 16 per cent of licence holders and were involved in 37 per cent of fatal crashes the previous year. Many of those killed were in cars driven by their peers.

The case for raising the age to at least 17 - and 18 before anyone can drive unsupervised - seemed overwhelming. Why has the Government quailed?

The obvious answer is the farm lobby. National's rural ministers and MPs will have listened to Federated Farmers about the need for young people in the country to drive to school. But they were asking only for an exemption for that sort of purpose, not a general right to drive at any time.

Or perhaps the Cabinet agreed with the Automobile Association, which thinks the minimum age is less important than the period of probation before a teenager can drive alone.

"Supervised learner drivers are the safest drivers on our roads," said the AA's spokesman. "The six months after they go solo is the greatest risk. Simply increasing the age is just going to kill them later."

The logic of that view would lead to no minimum age. Plainly, maturity is a factor, as it is for voting, drinking and much else of social interest. Eighteen has become the age of maturity for those rights and it has much to recommend it.

That is the point at which just about everybody has finished school and begins to make their life's decisions. It is soon enough to be in charge of a car.

The Government's decision to raise the age by only a year brings us into line with Canada and some states of America but will make little difference to our roads.

A longer probationary period will apply and there will be zero tolerance for drink driving under the age of 20. But no compulsory third party insurance, another need that has long been apparent to most people.

Yet the Government prefers the caution of its officials, who advise that compulsory third party cover would add little insurance value for a considerable administrative cost, which is hard to see. It could be easily administered as a condition of vehicle registration.

The Government fears it would leave more unregistered vehicles on the road. Defeatism rules.

Transport Minister Steven Joyce swept aside official caution to bring in a ban on hand-held cellphone calls in cars last year. He has not shown the same resolve on the latest round of road safety proposals. It augurs badly for bigger decisions that need to be made soon.