We all know we're exposed to pollution from exhausts on our way to work in the mornings - but just how bad is it? And is the air you're breathing more toxic if you're on a bike or in a car or bus? Scientists are setting out to find the answer to these questions and more.
While you can see the smoke and smell the fumes, the real enemy is invisible.
Microscopic toxic particles are in the air and even in your body.
For the next 12 weeks commuters will see scientists on bikes, in cars and on trains and buses.
The scientists are seeking to understand what impact your choice of travel might be having on your health.
"Most studies have said that the pollution that you're exposed to is worse when you're in a car and better when you're on a bike which surprises most people," says Canterbury University's Simon Kingham.
The thinking is when you're sitting in traffic in a car you're stuck right behind someone else's exhaust.
"Of course the place where they omit their pollution is exactly where you're drawing your air from, from their exhaust into your car," Mr Kingham says. "Whereas when you're on a bike the traffic's going past you most of the time or your going past the traffic."
But just recently other international studies have found the opposite.
"This is kind of what makes it so interesting," Mr Kingham says. "We actually don't know and we certainly don't know what's happening in New Zealand because there's been no study done here at all."
If you know you're heading into heavy traffic it probably pays to switch your air conditioning onto re-circulate ahead of time. Once you're behind that diesel bus its really too late to switch it - those toxic particles are probably already through your air conditioning vent and all around you.
The study is funded by the New Zealand Transport Agency and is being carried out by the top pollution scientists in the country.