The law allowing cyclists to ride two abreast is surely one of the more contentious road rules in Australia.
Bernard Carlon of NSW's Centre for Road Safety explains the basics like this: "Bicycle riders and motorcycle riders are allowed to ride two abreast in any traffic lane on single and multi-lane roads, providing they are not more than 1.5 metres from each other."
Despite the rules, riding two abreast still provokes fierce differences of opinion, as evidenced recently by various online polls, surveys and news reports on the measure, with many people calling for two-abreast cycling to be banned, saying it unnecessarily impedes traffic flow and can be dangerous.
Cyclists and cycling organisations have long argued the merits of riding two abreast, but what do roads and road safety authorities see as the benefits?
"Visibility" was the key advantage cited by the experts I consulted.
"Bicycles have little protection compared to motor vehicles, making bicycle riders more vulnerable in a crash," says Carlon. "Riding in pairs can enhance the visibility of cyclists to other road users."
Samantha Cockfield of Victoria's Transport Accident Commission says that "two people riding alongside each other in many circumstances are much more visible than in single file and that really is the key advantage in terms of safety. The key risk for riders is drivers who don't see them until it's too late, and get involved in a crash."
There are also advantages in being two abreast when it comes to overtaking. Cockfield says if the cyclists are "pretty much taking up a whole lane, a motorist has to formally overtake – they can't so much try and squeeze past".
This point is also highlighted in a VicRoads information page that describes riding side by side in pairs as "a formation with several safety benefits".
"By riding two abreast, [riders] are more likely to be seen by drivers and given more space," says VicRoads' Robyn Seymour.
"This also means they are less likely to be squeezed into the road edge by drivers, particularly on roads where there are hazards such as a steep drop."
Andrew Mahon of Queensland's Department of Transport and Main Roads describes riding two abreast as a "defensive riding technique which increases visibility".
It can also make for easier overtaking, he says.
"One of the advantages of having riders two abreast is other road users can get past them more quickly. If they're in a big group and single file, obviously it will take longer to get past them – if they're riding two abreast you may be able to get past them quicker.
"Of course, you have to make the right safety assessment before you overtake, particularly where it's single-lane roads and you might be moving into a lane with oncoming traffic - you need to make sure you allow enough distance to do that safely."
'No perfect answer'
As a rider, choosing to ride side-by-side or single file will depend on many factors, such as who I am riding with, how fast we're going, the type of road and how busy it is.
For example, on a road with bad sight-lines, single file might be preferable in case a driver approaching from behind is expecting the road to be clear.
I find many situations where riding single file makes things a lot easier – for me, for the riders with me, and for other vehicles. It's a constant tension between "doing my best to get other vehicles behind me in front of me – while still claiming all the space I need to be safe," as described by "gracious cycling" advocate Rob Berry.
The challenge is that bike riders make particular choices because they are often acutely aware of hazards that may not be apparent to motorists - such as the dangerous "door zone".
"For a cyclist there may be circumstances where, for whatever reason, riding single file might make them feel safer and more comfortable, but there might be circumstances where riding two abreast does make them feel more comfortable, more safe," says Mahon. "There's no perfect answer, there's no right or wrong answer."
And, of course, there is the need to be aware of the effects of your actions on other road users.
VicRoads notes that "depending on the particular road type, this riding formation can also impact on traffic flow and result in motorists having to drive behind cyclists and wait for a safe opportunity to pass".
The advice is for cyclists to "be considerate to other road users, and move into single file when it is safe to enable vehicles to pass".
Of course, there are times when bike riders can be inconsiderate, unaware, or just plainly in breach of the road rules, while social media is filled with tales of people being stuck behind cyclists.
But road users and roads authorities alike can attest to the advantages of being able to ride side by side.
Sure, cyclists riding two abreast may sometimes slow a motorist's progress. But they may also prove more visible, and the formation can lead to safer and easier overtaking.
As Mahon told me: "A minor inconvenience is exactly that – making sure everyone is safe is the most important thing."
Fairfax journalist Michael O'Reilly has written the On Your Bike blog since 2011.
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