It’s clear to just about everyone that Shane Warne is as good a commentator on transport policy as I am a spin bowler (i.e. really, really poor).

So as a result of Warne we get a week or so of the same old media merry-go-round. Cyclists should pay rego, yawn. Cyclists should always ride single file, blah blah blah. It’s a battle between motorists and cyclists, etc etc

Haven’t you got anything else? And this was right in the middle of the biggest bike racing event in Australia each year, the Tour Down Under. Quite possibly a time when we might expect positive media coverage of our sport/transport.

I had the responsibility (or perhaps misfortune) to be BQ’s representative for Channel Nine on the day they were looking for comment about Warne vs cyclists. Obviously I wasn’t either succinct enough or inflammatory enough, as they used other people’s sound-bites ahead of mine.

And later that day and the next, as I pondered my responses to the Channel Nine reporter, it continued to bug me just a tiny bit. Not the fact that they didn’t use what I said, but rather that is impossible that television news coverage can ever discuss a contentious issue in a way that moves public discourse forward.

So here’s my contribution to public debate around the topic of whether cyclists should always ride single file.

OK, you might want to grab a coffee or something, because this is going to take a while. Caveat: this is a work in progress, and I’m happy to hear of corrections to my (doubtlessly dodgy) maths.

Let’s establish some terms and conditions, set the scene etc.

First, a group of cyclists riding together two-abreast is a peloton, or a bunch. These riders are almost always sports or recreational cyclists. The bunch is a labor-saving device … a group of riders can go further and faster on the same energy output than if they all rode solo. But it is rare to see people commuting to work on their bicycles riding as a bunch.

Second, let’s make it very clear that riding two abreast is absolutely legal. And further, I will contend that in most cases around the streets of city and suburban Australia, that it makes sense for pelotons to ride like this, from a safety point of view as well as energy-efficiency.

So, why do cyclists ride in a peloton? And, indeed, why does the law continue to allow this as a special case. No other vehicles are given this dispensation.

And why is this the most efficient and safe way for sports and fitness cyclists to travel?

So let’s think about our road environment. An average traffic lane is 3.5 metres wide. A bicycle and rider are about 0.6 metres wide. Safe passing requires the driver of motor vehicle give a cyclist a metre of space. An average car is 2.2 metres wide, 4WD vehicles are wider, and trucks wider still.

I am sure that you are better at maths than I am, but already you can see that for a motor vehicle to safely pass a cyclist who is riding at the left edge of the road, the motor vehicle is probably going to have to use some of the oncoming traffic lane (assuming there’s no physical median strip).

Let’s give an optimum size for our bunch of cyclists. I will say no more than 20 in the bunch.  If the bunch is bigger than that, it becomes unwieldy for those in the bunch, not even considering the traffic around them. In a large bunch, there is an effect known as the bungee effect, which means that the riders are the back of a large bunch have a more difficult ride than those at the front.

But for this article, we are considering 8 to 20 riders to be the right size for a bunch.

Have a look at our perfect group of eight riders, positioned in the left lane in my beautiful graphic (done at accidentsketch.com if you need to make your own pix of bikes on the road). At 0.6 metres wide, and with a 1 metre gap between them, they take up almost exactly the same width in a lane as a standard car.

But at 12 metres long, this perfect little bunch is about three times longer than our mythical standard car.

Now let’s put ourselves in the driver’s seat of this mythical car, on a mythical street in mythical Brisbane.

The driver comes up behind a group of riders riding single file. As we’ve already established, the driver will probably have to do an over-taking manoeuvre which includes using the on-coming lane, regardless of whether the group is single-file, or riding as a peloton (two-abreast).

And now we begin to see the advantage of the peloton, to both rider and motorist.

Even if our group of eight is riding single-file, their perceived width from the following motorist’s point of view will be substantially wider than a solo cyclist. That’s because its not practical or even possible to ride in a perfect straight line. So let’s say the single-file riders make up a perceived width of 1.2 metres, even though each of them is only 0.6m wide when the car passes them individually. Add in 1m of safe passing distance, and roughly half of our 2.2 metre wide motor vehicle is on the oncoming side of the road.

And because the single file group, even at eight riders long, is already experiencing some of the bungee cord effect, the single-filers group will be more than twice as long as a peloton. I estimate an eight-rider peloton to be 12-15 metres long. In single file, that same group will be 30-40 metres long.

So what does that mean for the driver? It means more time on the wrong side of the road.

Now, at this smaller size of group, the difference seems small. If the bunch is riding at 30 km/h in a 60 km/h zone, we are talking 5 seconds to pass a peloton vs 8 seconds to pass a single-file group.

But let’s take the example out to the 20-rider bunch. It’s 30-40 metres long in peloton form. And 60-80 metres long in single file.

Now it’s 8 seconds to pass the peloton, and about 11 seconds to get past the single filers.

And more than 10 seconds is a long time to be on the wrong side of the road. That means the driver needs longer line-of-sight to overtake the group, it means a cautious or nervous driver will sit behind a single-file group for a long time before attempting to pass.

So that’s my view on the subject. A two-abreast peloton causes less disruption on most occasions than single-file riders. But pelotons of more than 20 riders are too big, and should split themselves up, both for their own benefit and that of the drivers around them.

The maths to calculate passing times is here. Thanks to Sholto for his help.

Interested to hear what my readers think on this matter!