"Smoking in the car is different to smoking in a room because once the windows are down the smoke goes out," says Henry Barry (31) from Cork.
Henry doesn't drive himself but says that when he is travelling with his partner, she doesn't mind him smoking once a window is left open. "And I only smoke on long journeys," he says.
The general perception of smoking in cars seems to be that, once a window is open and the smoker takes care to smoke out the window, it doesn't do much damage to anybody aside from the smoker.
However, Dr Fenton Howell, a GP from Drogheda, is quick to dispel this myth.
"A bit of common sense is needed here," he says. "The truth is that smoke doesn't just go straight out of the window. When the car is moving, the air is blowing back into the car and so the smoke circulates around."
If it's raining or cold, says Howell, people don't keep their windows open - "but even if they did it's not a solution to the problem."
The damage caused by passive smoking, particularly to children, must not be underestimated, he says. A recent survey by Ital's tobacco control unit suggests that cigarette smoke produces 10 times more air pollution than diesel exhaust.
According to Howell, children are all too frequently the principle victims of passive smoking in cars simply because they have no choice and are effectively a "captive audience".
"You see it now already in the first few weeks of term time - parents driving with cars full of children and subjecting them to cigarette smoke. It's very irresponsible.
"For children and young people, it increases the risk of them developing asthma as well as other respiratory infections. The younger the children, the more damage done."
One motorist, Ms Noreen Flynn, from Castlerea, Co Roscommon, says she is well aware of the negative effects of passive smoking. "I don't smoke in the car if there is a baby in it or if I'm carrying people who have asthma or other problems - but I'd still smoke if there are older kids."
However, she says, it's only in recent years that smokers have developed this awareness. "Before I would have smoked all the time in the car because the dangers of passive smoking hadn't really been highlighted. You just didn't think about how it affected anyone."
While the smoking ban has made some smokers more thoughtful, this doesn't apply across the board. Ger Flynn (32), from Waterford, says that he never smokes when his father or sister are in the car, but if it's a hitch-hiker it's a different story.
"I figure if they want to get a lift in my car they have to take what comes with it," he says. "If they didn't like smoking, I'd give them the option of getting out."
For some, the car has become a sort of smoking sanctuary. Gary Byrne (29), from Donnycarney, Dublin, says that, when it's raining at work, he smokes in the car.
Another smoker who was unwilling to disclose her identity says: "Often when I get into the car, I've just been somewhere where I can't smoke, so I'm dying for one."
According to Dr Howell, the negative effects of smoking in cars are simply too significant to ignore. It's not just the smoke that's an issue.
The movements involved in smoking distract drivers," he says, "and you increase the risk of an accident. If you must smoke, have one before getting into the car or after getting out of it."