Bad habits creep back all too readily if not enough is done to prevent their reappearance. The more ingrained the habit, the more serious is the problem. So it is with the many motorists who are openly flouting the law that bans the use of hand-held cellphones while driving.

This week, in just one hour, the Herald observed 50 drivers using their phones on one of the busiest stretches of motorway in central Auckland.

Thirty-three drivers were texting and 17 were talking. The number was far higher than that in two unscientific surveys from the same spot in the week after the ban became law last November.

It is not too difficult to understand why this has happened. In the first instance, drivers were given a period of grace after the ban was introduced. While well-intentioned, that gave the wrong signal in terms of how seriously the police viewed the offence.

Then there is the difficulty of strict enforcement. Catching cellphone users requires close observation by officers, not a simple recourse to technology as with, say, speeding tickets.

Thirdly, there have always been doubts about whether the penalty for breaching the ban - a fine of $80 and 20 demerit points - would be enough to deter the practice given its widespread and deep-seated nature.

These problems are not insurmountable. A start has been made to addressing them with a TV campaign about the dangers of driving and using a phone.

More will be needed. In some ways, there are parallels between the cellphone ban and the law that made it compulsory to wear seat-belts.

The flouting of that law was also quite difficult to detect, and the small minority who declined to wear seat-belts talked a lot about their rights. What all the available research said about good safety practice seemed not to matter to them.

Concerted police campaigns targeting drivers who were not buckling up finally pulled that group into line. A similar focus may be required for cellphones.

If not, an obvious alternative is raising the penalty for breaches. A more effective deterrent might be a fine of, say, $150 plus demerit points. But even that will be rendered ineffective if the law is not strongly enforced.

Coincidentally, the sum of $150 is also that imposed by the Auckland City Council on drivers who enter bus lanes more than 50m before making left turns.

So far, it has issued $4.2 million of infringement notices over 12 months to drivers who have breached the regulation. Not only is the council's response grossly disproportionate to the size of the problem but the penalty is out of kilter with those levied for road-safety transgressions, including the cellphone ban.

At least the latter is a significant problem. An AA Insurance survey of drivers released last month found motorists using phones was the leading frustration for other road-users. Drivers fear the danger posed by those distracted by talking or texting.

Nothing like the same risk results from bus-lane breaches on congested city roads. Worst of all, the council could largely solve the problem by placing a marker 50m from left turns on bus-lane roads. Drivers could then judge when to enter the lanes.

The Minister of Transport, Steven Joyce, says he will "wait until the figures come through" before deciding whether to take further steps to enforce the cellphone law.

He has already demonstrated a welcome appreciation of the problem, not least in acting briskly to introduce a ban after years of procrastination by the previous government.

Clearly, there is still much apprehension among motorists about the ongoing risk posed by cellphone users. They will applaud if Mr Joyce does more to make the roads safer.