When Mosman Council issues tickets to mothers double parking outside school during the drop-off and pick-up hours, the notices are posted out. Most land in mailboxes that are one, or at a stretch, two kilometres from the school.

But it is not just Mosman mothers who are guilty of firing up a two-tonne four-wheel-drive every time they need to get to the corner shop. Sydney mothers are inveterate car users. The wealthy ones, the not-so-wealthy ones, inner city or suburban, we are nearly all guilty of treating a carbon-coughing vehicle like an oversized baby bag.

I write this having just driven 14 kilometres to drop my four-year-old at a friend's house. I'll drive it again to pick her up, but not before I've popped out at least twice with the one-year-old to Woolworths or a playground I can see from the house. And if she falls asleep in the car, I may just drive around for another 20 minutes to let her continue sleeping. Really, the only green aspect of my transport habits is the Vegemite sandwiches composting on the back seat.

I'm not alone. At 3.30pm, according to the NSW Department of Planning's Sydney Household Travel Survey, nearly one-in-four cars on the road for non-discretionary purposes (that is, trips that have to be made somehow) are picking up children from school.

During the morning peak hour, cars involved in the school run tend to stay out longest, driving an average 16 kilometres. And the drivers of any trip that serves another passenger during the morning peak are overwhelmingly women, aged 31 to 50, who are "unemployed or keeping house" or in "casual and voluntary employment". That's us, ladies.

But at the same time, it is often we mothers who lead the charge when it comes to making greener choices in most other areas of family life. Research by the NSW Department of Environment found that parents are more likely than single people to engage in environmentally friendly behaviours such as reducing water and energy consumption and avoiding products with lots of packaging. Women rate the environment more highly on their list of concerns than men. So is it by choice or necessity that even the greenest mothers cannot stop driving?

"It is very difficult to do everything you have to do with children on public transport," says Alex Duchen, a 42-year-old solicitor and mother of three children, aged nine, seven and two. "Even though I have a train, a ferry and a bus in my area, which I use when I go to work, you have to be in too many places at too many times, in terms of managing children.

"With seven bags of shopping, the two-year-old and the baby bag, it is already physically exhausting, without having to battle with the bus as well."

But Duchen is by no means unconcerned about the family's ecological footprint. Since reading Tim Flannery's The Weather Makers, she has, among other things, shut off the air-conditioning, replaced her washing machine with a more economical model and switched to 100 per cent accredited GreenPower. The house has been audited by a sustainability consultant and many of the light bulbs replaced. Heating off and jumpers on is family policy indoors.

But still, there was the problem of the car, a large Volvo four-wheel-drive. "I did feel sick about driving it," Duchen says. "It just seemed ridiculous to be driving this tank around with just me in it most of the time." Since selling the car would not, she felt, solve the problem, the family now uses it only for holidays, replacing it with a compact diesel station wagon for the city.

Until the children are old enough to walk to school or American-style school buses are adopted in Sydney, these sorts of cumulative changes may be all car-reliant mothers can do. But that is OK, according to Danielle Ecuyer, founder of Women For Change Alliance, an environmental education group.

"It is important," Ecuyer says, "not to view car travel in isolation and feel, 'Well, I can't change it so I'm defeated.

"There are things you can do - be creative in the ways you use your car. Can you car-share for school pick-ups? Can you look at trip planning, to be more efficient with your driving, and walk some of the time?"

And since you do not have to vacuum the back seats of a bus or put the same Wiggles CD on an endless loop, there may be some lifestyle advantages to public transport we had not yet thought of.