There's anecdotal evidence that using a mirror while cycling improves safety. It seems logical. So like bells and lights, does it follow that mirrors should be mandatory when cycling on roads?

Film-make Mike Rubbo is surprised at how few cyclists fit rear-view mirrors to their bikes or helmets:

I can’t understand why since I find the awareness of what’s behind which a mirror gives is crucial for my safety when I’m on a bike. I can’t do effective head checks which see directly behind and I think few people can, not without wobbling all over the place.

So he’s made this short film, No bike mirror…suicidal?, to encourage cyclists to think about the safety benefits of using a rear-vision mirror when they’re out riding on roads.

Rear view mirrors are now available for all styles of bike, they’re lightweight, and they’re cheap, especially via on-line stores. While some are complete junk, there’re also models that are pretty good e.g. hold position, minimise vibration.

Mike’s objective is solely to raise awareness of the benefits of mirrors, but the obvious public policy question is whether or not cyclists ought to be compelled to fit a mirror. After all, in most jurisdictions they’re already required by law to have a working bell and front and back lights at night.

At the outset, it would be necessary to be confident that mirrors really do improve safety substantially and that the savings in private and social health costs from avoided injuries would justify the law. It might look like mirrors improve safety, but if most cyclists wouldn’t use them they’d provide little benefit.

Some cyclists would much prefer to continue relying on a head check and their ears rather than be compelled to buy and fit an accessory they’d regard as unnecessary.

There doesn’t seem to be much research on this issue, although here’s one (old) study that says cyclists with mirrors have a lower crash rate. But rather than indicating the usefulness of mirrors, that might simply show that more risk-averse cyclists are both less likely to be involved in a crash and more likely to have a mirror.

On the other hand, motorcyclists are compelled to have them so that could be taken as a prima facie case they’re worth having. Further, a significant proportion of crashes resulting in serious injury are caused by a vehicle approaching the cyclist from behind.

Assuming it can be established reliably that mirrors really do confer a safety benefit large enough to warrant considering making them mandatory, what are the downsides?

Unlike the debate about the law mandating helmets, it’s hard to see that compelling cyclists to have a mirror would suppress cycling on a significant scale. But if you’re not persuaded mirrors are sufficiently beneficial, it’d be yet another minor expense and inconvenience, especially if you’re the type who doesn’t have a 20 gram bell because of the weight burden.

I expect some would see it as adding to the idea that cycling on roads is more dangerous than it really is. Some might also argue placing responsibility for safety on the shoulders of cyclists gives governments an alibi for not investing in cycling infrastructure.

And then there’s the ‘nanny state’ argument; that governments should let cyclists make their own decision on matters that concern their personal welfare.

The nub of it is whether or not the savings in avoided health costs from avoided injuries exceed the negatives of compelling all cyclists to fit a mirror. If they do, then prima facie it’s worth doing.

However even if it’s clear the ratio of benefits to costs is positive, it doesn’t necessarily follow that mirrors should be made mandatory. As I’ve noted before, many behaviours are simply too hard to regulate so we cop the social cost.

It might be, for example, that a proposed regulation is too hard to enforce; or it’s too inconvenient; or it offends too many people’s sense of what’s fair and equitable; or we think some behaviours just shouldn’t be regulated.

Personally, I’m a fan of mirrors and will continue to use one. But there’s much to be said for the view that governments should tread lightly when it comes to regulation, especially if the evidence base isn’t large.

Mike Rubbo favours an awareness-raising campaign over compulsion and has gotten the ball rolling with his film. I think that’s the sensible way to go. It probably won’t persuade too many “weight weenies” but there are plenty of other cyclists who I suspect would see the advantage of using a mirror once the issue is explained.

There’re lots of studies of cycling safety (especially helmets) so I’m surprised researchers haven’t given more attention to mirrors. It seems to me it’s an area worth investigating.