It is one of our great national idiocies that while we're spending billions on transport infrastructure trying to unclog the nation's roads, we're still letting people park on them, writes Alan Kohler.

Australian governments are spending billions of dollars on transport infrastructure trying to unclog the nation's roads, and yet they still let people park on them.

It is one of our great national idiocies that the capacity of busy roads is reduced by 50 per cent for most of the day because a few cars have been left on them, sometimes for long periods, blocking one of the traffic lanes.

In fact, I'd go so far as to say most of the national infrastructure budget on roads and public transport is being spent to make up for the failure of weak-kneed politicians to force parked cars off the roads.

We need more and better public transport, it's said, because the roads are clogged. Well yes, but the roads are clogged because most of the time you can only drive on half of them.

It's true that all cities have "peak hour" clearways, usually lasting two hours in the morning and afternoon.

But these were introduced more than two decades ago, when peak hour actually existed.

Now the traffic in most cities is horrendous more or less all the time, including on weekends. The volume of cars on the roads has increased enormously over the past 20 years, yet clearways have barely changed in duration or extent. The weekends, for some reason, have become the worst of all. Yet nothing has been done.

Shopkeepers, of course, complain bitterly about the brief clearways that exist now and remonstrate loudly when any politician attempts to extend their hours.

And it's true: most strip shopping centres would be totally ruined by a permanent parking ban because there is usually nowhere else to park but on the road.

But shopping strips already seem to be hollowing out because only the malls, with car parks, are surviving the advent of online shopping.

However, it's a tough life for the shops that are still hanging on, and they employ a lot of people. More parking restrictions would tip many more of them over the edge.

And that's the main reason clearways haven't changed much in 20 years. The small businesses that line the roads have a much louder, more focused political voice than the general population of motorists.

In addition to spending $8 billion on a questionable tunnel, the Napthine Government in Victoria has promised as part of its campaign for the November election to create a permanent clearway on Melbourne's busiest road, Punt Road, between St Kilda Junction and the Yarra River.

This road is three kilometres of daily hell, made doubly hellish by the occasional cars parked ridiculously in two of the four lanes.

There are almost no shops along this bit of road, which is why the state government has plucked up the courage to do something about it. But even so, it has taken years for the government to do the obvious.

Moreover, the other side of the river where the road turns into Hoddle Street is, if anything, even worse and it's also blocked by stationary cars; no mention of that in the election policy, though. Instead the Victorian election has become a referendum on the East-West Link project, when in fact Melbourne's main traffic problem is north-south (Punt Road and Hoddle Street).

Any strategy to ban parking on busy roads needs to take account of shopkeepers, and for that matter the residents who don't have off-street parking and would be forced to walk a long way, often in the dark, if they couldn't park out the front.

It seems to me that infrastructure budgets would be far better spent developing car parks to increase the capacity of existing roads by 50 per cent, than on expensively trying to get around the problem with new toll roads and tunnels. At least that, you might think, would be a good first step.

The problem, of course, is that wouldn't involve grand ministerial project announcements.

It would involve lots of little things. Buildings would have to be bought and demolished to create car parks behind shopping strips. Nature strips could be removed and footpaths narrowed to provide for street parking bays. Residents could be given financial assistance to create off-street parking on their properties.

In the 1990s, Adelaide went through an extensive road-widening program to create new car parking on many significant roads. Many buildings (including shops and houses) were demolished and rebuilt a few metres back.

That sort of thing would be prohibitively expensive now because of the increased cost of land. But there are plenty of other things that could be done.

A clearways strategy document issued by the NSW Transport Department last year concluded:

The deterioration in travel times and speeds are now at a level where the benefits of clearways could be extended through the day on certain roads during weekdays, and extended to weekends where the traffic conditions are similar to weekday peak periods.

But nothing has happened, beyond a weekend clearway on Victoria Road. Apparently the Government is looking at extended clearways in Military Road, but is baulking at the ferocious opposition of the Cremorne and Mosman shopkeepers.

Fundamentally, the community has to ask itself: can we still afford to allow cars to be parked on main roads?

As we sit, stationary, whiling away the minutes in traffic, having had to dangerously diverge out of the other lane because a car was parked in it, the answer is "NO".

And it's not just about frustrated motorists. National productivity is being greatly reduced by the state of the nation's roads, much of which, I would argue, is caused by unrestricted parking.

And that's without even mentioning all the bicycles that dangerously infest the roads these days. But don't get me started.

Alan Kohler is finance presenter on ABC News. He tweets at @alankohler. View his full profile here.