cars, pedestrians, bicycles, all mingling in street

Relative Risk

Government data and statistics can be famously hard to obtain but as successive Australian federal governments move to provide more information online we can access quality data to look at claims of road safety. Both the Australian Bureau of Statistics (census data) and the Bureau of Infrastructure, Transport and Regional Economics provided historical data sets for this analysis of relative risk.

State governments are attempting to move to digital platforms but the detailed Victorian road crash data greatly under represents pedestrians and cyclists in its reporting, so the road toll numbers have been taken from BITRE data which includes breakdown by state. The widely used metric for transport mode share is the Australian census, which asks how people travel to their place of work. Here the national numbers are presented with Victorias contribution indicated by the transparent lines:

commuting volumes and road toll over 20 years

Using a log scale to compare the large ratios the trends are for increasing total commuting volumes with nationally stable volumes of pedestrians and cyclists, while in Victoria these non motorised transport modes are on the increase. Although only capturing commuting transport these are the typically reported statistics for cycling mode share, comparing to BITRE data for total urban mode shares the census commuting data surprisingly matches well to the 4% mode share by distance travelled, rather than the 33% non motorised mode share when counted by “trips”. What is more interesting are the trends of these statistics, at the same time as use is increasing overall road toll is steadily declining, but the the road toll of cyclists has been steady.

So for these two non motorised forms of transport we can compare their share of the road toll, with their mode share by distance travelled for an estimate of relative danger:

declining relative risk of non motorised transport

A ratio of 1 would exist when the transport mode has equal representation in both fatalities and mode share, but here the non motorised forms of transport are over represented. For a journey of a given distance (going shopping for instance) walking is approximately 4 times more likely to kill you than driving a car, and the chance of being killed while cycling is just over twice as likely when compared to motorised transport. Great improvements can be seen in the cycling safety in Victoria, at the same time as cycling rates are increasing the risk of death has dropped by a factor of 2. Pedestrians however are missing out on road safety improvements. The general solution being to limit ones exposure by avoiding travelling or taking the “safer” car, but is this really fair?

First consider the ratio of “single vehicle” accidents for different modes of transport, here the fraction of all deaths for each mode that occurred without another vehicle involved, breaking motorcycles out from other motorised transport:

ratioSingle.gif

This is across the period of January 2001 to July 2016 to match with other sources of data, noting that pedestrians are not counted as road deaths unless there was a vehicle involved so their ratio is reported as 0 here. Motorised transport is killing its passengers without the need for other vehicles to be involved, but cycling deaths are dominated by crashes involving motor vehicles. Adjusting this data for the excess fatality factor of 2 for cycling and in the absence of other traffic (single vehicle accidents),

without traffic riding a bicycle in Victoria is safer than driving a car when travelling the same distance.

We can also count the total number of pedestrian deaths from vehicles at 3131 over this period, 4 of which involved a bicycle hitting and killing a pedestrian in an accident (there was 1 additional intentional use of a bicycle as a weapon that killed a pedestrian). Taken with the mode share by kilometres travelled of bicycles at under 1% it would be expected that if bicycles were as much of a threat to pedestrians as cars their toll should have been 27. Even with the lack of adequate separation between the modes in Australia (a factor in one of the incidences),

in Australia bicycles are 7 times less likely to kill pedestrians per kilometre travelled when compared to motorised transport.

This could be greatly improved by untangling pedestrian and bicycle routes, just as cars and pedestrians don’t routinely share the same space. So if bicycle use can reduce pedestrian deaths and are safer over the same distance could replacing cars with bicycles reduce the road toll?

At an elevated risk factor of 2 we consider the alternative of taking all cyclists off the road and placing them into cars, this would have reduced the national road toll by approximately 290 over the 2001 to 2016 period with cyclists instead in cars to protect them from the other cars, and raise the road toll by approximately 23 for the additional pedestrians killed, but an overall reduction in the road toll.

Bicycle riders are greater than 100 times more likely to be killed than kill someone else when riding their bike in Australia.

From this asymmetry incrementally replacing cars with bicycles on a small scale would increase the road toll (entirely through excess deaths of cyclists) until some maxima at which point the reduced car numbers would cause the risk factors to pedestrians and cyclists to drop, then the road toll would decrease with further reduced car use. But how far away such a turning point is remains unknown and for now Australia is stuck on the car dominated side of the curve lacking any politically tasteful impetus to push over that barrier. Making cycling safer could reduce the road toll, but this data highlights the overlooked need to greatly improve the protection of pedestrians from motor vehicles.

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