Minding the gap – and the door zone


One of the major issues we have when riding bikes is cars passing too close. The Road Code recommends a minimum 1.5m passing distance.  I recently decided to see how close cars actually pass people riding bikes. I was also interested in how close cyclists ride to parked cars – “dooring” is a significant cause of cycling accidents, and the Road Code recommends that cyclists stay at least 1m away from parked cars.

I chose two locations, Aro Street (going uphill) and Oriental Parade (heading into town), where there were a significant number of cars passing cyclists and parked cars. I photographed passing incidents, and estimated the distance between the cyclist and the passing car, and the cyclist and the parked cars. I used the diameter of the bicycle wheel as the “ruler” for measuring this – although there are different diameter wheels, in practice there isn’t much difference between a 700c wheel which generally has a thin tire and a 26″ wheel which generally has a fatter tire. There are also inaccuracies in estimating which parked car the cyclist was close to, and where the car was in relation to the cyclist. However I think the method enables some general observations to be made.

I recorded 69 passing incidents, 46 in Oriental Parade, 23 in Aro Street. On average, people driving cars are pretty good about keeping to the recommended 1.5m. The average passing distance was 1.78m: 1.94m in the more spacious Oriental Parade, where there is a 1.5m bike lane and a 3.6m lane; 1.46m in the more constricted Aro St where there is no bike lane, and the vehicle lane is generally about 2.8m between the centre line and the parked cars. In 78% of the passing incidents the gap was greater than 1.5m, only two passing distances in Oriental Parade were less than 1.5m. The closest pass was just under a metre.

On the other hand, people riding bikes have a strong tendency to ride in the door zone, on average riding 0.84m from the parked cars (1m on Oriental Parade, 0.51m in Aro Street): in 65% of the incidents the cyclist was less than 1m from the parked cars.

Many people feel that by riding close to the edge, they lessen the risk of being passed at an uncomfortable distance. However in these passing incidents, there didn’t seem to be any correlation between how close people rode to the parked cars, and how close cars passed them. If anything, there was a slight tendency the other way: people riding further out tended to be passed with a greater gap.

What does all this mean for us as cyclists? The lesson I take from this is that riding outside the door zone doesn’t make you more vulnerable to being passed uncomfortably close. So it makes sense to stay out of the door zone. I also wonder if campaigns for a 1.5m passing distance by cars need to be complemented by a similar campaign for cyclists to ride 1m out from parked cars: apart from delivering the message to cyclists, this would also help motorists understand why cyclists are riding out of the door zone.



7 thoughts on “Minding the gap – and the door zone

  1. Nice piece of research Alastair – is the distance measured from the centre of the bike or the extremity (handle bar or shoulder)?
    I certainly see scope for an education campaign, on my rides I have visualised posters showing two views, one with a cyclist riding 1.5m out from a parked car (label: “I’m not passing this”), the second showing the same view with the car door open (label: “I’m passing this”).


    1. Good point, Bruce. I measured from the centre of the bike. So the actual gap could be 30cm or so less than the figures I’ve given. But there would have been issues about judging where the “extremity” was, so I decided to keep things simple by measuring from the centre (actually the point where the wheel touched the road).


  2. Nicole

    Very interesting research… I suspect you could even turn this into a journal article and boost your PBRF?!
    I will now be keeping a greater distance from the door zone thanks to your findings.


  3. Rob

    It takes confidence to ride out of the door zone and in the actual flow of traffic, but it has to be done. I do it every day on part of my commute where the road narrows with no shoulder. If a car is behind me when the narrowing happens, they stay there until I decide it’s safe for them to pass. I try and keep a good pace to minimise the delay, but I don’t blow an o-ring over it.


  4. Pingback: Handy Tips: Avoiding Dooring | Cycling in Christchurch

  5. Pingback: Handy Tips: Avoiding Dooring – Cycling in Christchurch

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