Cyclists are suffering more serious injuries in road crashes than ever before, leading to significant disability, our new study shows.

But what is less clear is what's behind these injuries, which are occurring as the number of people who died in road traffic crashes has fallen.

In our study published today in the Medical Journal of Australia, we investigated deaths and serious injuries after traffic crashes in Victoria from 2007 to 2015.

We looked at whether deaths and serious injury rates for all road users changed over time. We also looked at the disability and economic costs of these injuries.

The total number of deaths from road traffic crashes fell over the study period. But rates of serious road traffic injuries did not.

Cyclists involved in more serious crashes

There were 10,092 road traffic deaths and serious injuries over the course of our study.

This led to over 77,000 disability-adjusted life years (a measure of overall disability burden, expressed as the number of years lost to disability or early death).

The estimated health costs associated with these road traffic injuries (known as "health loss" costs) was more than $14 billion.

Most concerning was the rise in serious injury rates in cyclists, which increased 8 per cent a year. In fact, the absolute number of cases more than doubled over the nine-year study period.

These injuries are often severe, including head injuries, spine injuries and fractures of the pelvis and limbs. They often lead to significant disability.

Over the course of our study, a rise in such serious injuries led to a 56 per cent increase in disability-adjusted life years; health costs for cyclists were more than $700 million.

Why are cyclists' serious injuries rising?

However, it is not clear what's driving these increases in serious injuries.

In a previous study, we interviewed cyclists admitted to hospital after a crash. Of the crashes that occurred on the road, 52 per cent involved another road user, most commonly a motor vehicle.

A total of 22 per cent of all on-road crashes also occurred while cyclists were riding in a marked bicycle lane, demonstrating they are not sufficient to completely protect cyclists.

While these on-road bicycle lanes provide dedicated space for cyclists, riders remain close to motorists and people in parked cars opening doors.

A total of 48 per cent of on-road crashes only involved a single cyclist.

While we need more research to better understand the single cyclist-only crashes, researchers have previously found the condition of road surfaces, distraction, mechanical issues and speed are possible factors.

About half of the crashes involved a single cyclist. ( ABC News: Josh Mullane )

Are more people cycling?

One of the limitations of our study was that we couldn't adjust for the amount of time or distance cyclists travel each year.

Unfortunately, we have very limited data on this in Australia.

The National Cycling Participation Survey is a telephone survey that asks how many times people cycled in the past week, month or year.

The 2017 results showed the proportion of people who had cycled in the past month declined from 27 per cent in 2011 to 22 per cent in 2017.

While cycling participation overall may have declined, there may be an increase in the overall time spent riding, or the number of cyclists riding on the road, compared to on bicycle paths, for example.

So, what does this mean for cyclists?

So, is the message from our study, "don't cycle"? No, not at all. The health and economic benefits of cycling are well established.

A recent UK study demonstrated that cycling to work was associated with a 41 per cent lower risk of early death compared to commuting by car or public transport.

And while cycling-related injury rates are on the rise, they made up only 11 per cent of serious road traffic injuries.

It is clear we need greater investment in cyclist safety. We know being concerned about safety is one of the biggest barriers to people cycling.

Cyclists may be spending more time on the road in recent years, which could explain the results. ( AAP: Joe Castro )

Interactions with motor vehicles — not just collisions, but also being in the presence of and close proximity to motor vehicles — and the absence of appropriate cycling infrastructure are some of the most common barriers people mention.

Dedicated bike lanes that are separated from traffic are an effective way to reduce serious injury.

While we need to invest more in cycling-specific infrastructure (like bike lanes and bike paths) it is often not feasible to have this across an entire road network.

So, we need a multi-faceted approach to improving safety for cyclists.

Reducing the speed limit in residential streets to 30 kilometres per hour has been proposed as a way to improve safety for vulnerable road users, and a trial has recently been announced in inner Melbourne.

We also need to improve the culture around cyclists as legitimate road users, through changes in legislation, education and training for all road users.

Given the rising injury rates in cyclists, we need government and road safety organisations to act now to provide a safer environment for cyclists.

Ben Beck is a research fellow at Monash University.

Originally published in The Conversation