Summer is a Time to Ride, a Time to Crash

bike jumpMemorial Day, July 4th, and Labor Day holidays are the traditional signposts of summer. Each respectively marks a change in the national mood, from optimism at the opening of the season, then the high point of leisure & recreation, and finally that abrupt return to our regular rhythms. But each is a reminder to causal riders and committed cyclists alike that it’s time to get out and ride. These long days and warm nights of summer are made for cycling whether to the grocery or the beach or simply to run that errand in town. But Summer is also the season when America’s favorite pastime is more likely to result in bike-related injuries. Let’s take a look at the trends.

With Independence Day just behind us and two more months of summertime cycling ahead of us, let’s remember that most serious injuries happen in the summer months. That should be no surprise: more folks ride in summer. Our climate of abundant sunshine and moderate temperatures make cycling comfortable; and long days and low rates of precipitation make it more practical than driving. Even the most motor-minded of us can get out from behind the wheel during to enjoy a ride to the grocery. (Heck, a few of us are known now and again to ride clear across town for a coffee. It’s about the ride; the coffee is a grace note!)

While the incentive is great to get in the saddle, we must keep in mind that we need to protect ourselves when we’re riding with motor traffic without the benefit of sheet metal protection.  The most immediate thing we can keep our bikes in safe working order. Solo crashes comprise a surprisingly large share of bike injuries, so before setting out do a simple pre-trip check: squeeze the brakes, pinch the tires and make sure you’re equipped with appropriate reflectors and lighting (both are required by law for night riding). Then there’s the helmet: it can make the difference between scrapes and bruises and concussions and worse. It is optional under the law but is a common sense step to take.

This post is not about solo mishaps but instead addresses collisions with motor vehicles. It is a danger that cyclists and pedestrians face every day as soon as we depart the sidewalk or driveway. Here we draw on the California SWITRs database for statewide data during the period 2005-2009 in order to identify a few key trends. As we ride this summer, and then look ahead to the seasons beyond, let’s base our pro-bike advocacy efforts on solid support: data, data, data!

Seasonal Trends

Cyclists injured by month 2009 chart According to the data, there is a clear seasonal dimension to bike-involved collision injuries. Take 2009 for example (left): the data show a slow build in injuries from the depths of winter to a broad peak in late Summer. That peak lasts well into the Fall. But when Daylight Saving Time kicks in on the 2nd weekend in November, there is a precipitous decline through the Winter months only to recover sharply afterward in the Spring.

What accounts for a near doubling of statewide monthly injuries in 2009 between the Winter and the Summer? Certainly there are more cyclists on the road in season. But it could also be the climate: in the southern part of the state sees more precipitation in the December to February months which puts a damper on the will to ride. And likely the extended daylight hours affects our decision whether or not we ride. Shorter days mean riding in the dark, and it’s likely that only the committed cyclist undertakes that challenge. With fewer casual cyclists perhaps the balance of more experienced cyclists depresses the serous injury rate? You tell us.

That seasonal rhythm also plays out consistently year-to-year, as illustrated by bike-involved collision injuries charted quarterly from 2005 to 2009 (below):

Cyclists injured by quarter 2005-9 chartIt is no surprise that we see a cyclical seasonal pattern repeated. As mentioned, Summer days invite people to pursue leisure activities that might include a bike trip, and coincident with that increased popularity may come more injuries. Now, any serious injuries are cause for concern. And here at Better Bike we’re working with our police department to identify hotspots in closer to real time than stale state data could show. But more than the aggregate number of injuries it’s the upward trend that’s worrisome.

Injuries on the Increase

We’re seeing here the darker side of seasonal popularity: a spike in the summer and a steady march toward of serious injuries coincident perhaps with the increased popularity of cycling. Not scrapes and bruises, mind you, but injuries sufficiently serious to warrant medical attention and at the least the filing a police report. (If you are injured in a collision, always file a report. Insist on it!) Practically, where there’s serious injury there is likely to be an effort to recover. And damages often rest on fault. These SWITRS data are quite detailed – indicating fault if determined and noting contributing factors and even if the driver fled the scene – but here we’re just skimming for the big picture.

What to make of the upward trend? If more cyclists are taking to the streets coincident with a renewed popularity of cycling, shouldn’t the safety-in-numbers argument prevail? Greater visibility should increase awareness by drivers and thus reduce the rate of collisions and resulting injuries. But here we’re looking at absolute numbers and not rates, so we can’t infer whether the argument holds. All we know is that we’re seeing more injuries.

Perhaps inexperienced riders unfamiliar with road rules or without skills training may find themselves more vulnerable to crashing. Cycling is also becoming more popular as a sport and attracting more folks in their middle years, especially in the Summer. Maybe that many more riders introduces much more road conflict.

By the same token, shouldn’t the longer days and lighter vehicular traffic of Summer temper the effect of a seasonal increase in cyclists? Again, maybe a much greater number of casual riders in season simply overpowers whatever safety gains exist. And who knows – maybe lighter traffic on our wide roads carries increased risk because traffic can then flow at a greater speed. Had we accurate bike counts and surveys we might know more about who’s riding in and then understand why they’re injured more frequently in summer…and why that overall injury trend is on the rise. We need better data!

Fatalities on the Decrease

Cyclists killed by month 2009 chartFatalities show a different view of the safety problem. Thankfully there are many fewer fatalities than serious injuries – on average about only 1% of incidents reported to police result in a fatality – and overall on a seasonal basis, the reported fatalities do track injuries.

Here we see a pronounced upward trend between July and November of 2009 (right) despite a curve that shows greater variation (owing to the overall fewer fatalities). Squint and you still see the upward trajectory through the year. Again, a seasonal pattern.

A finer-grained picture comes into view for the 2005-2009 period when fatalities are tallied by quarter and then charted:

Cyclists Killed by quarter 2005-9 chartWe see that fatalities regularly peak in the third quarter (Autumn) of every year, while the troughs come every Winter (Qs 4 & 1). That follows the same general pattern as injuries, but the good news is that the trend is favorable: the downward slope means that we’re seeing fewer fatalities every year over that period.

Cyclists Killed and Injured: change from 2005 to 2009 chartAnother way to look at that data is to compare annual rates of change. We see that that the fatality trendline is clearly moving in an opposite direction from injuries (as noted earlier). In fact, the subordinate position of the fatality plot not only depicts a slower rate of growth compared to injuries statewide, but shows a negative rate of growth – a decline year-over-year – for bike-involved fatal collisions (as we noted in the previous paragraph). While the jagged plot and four data points across the five year period presents a rough sketch, we need not smooth it: the trend is clearly downward and favorable.

Cyclists Killed and Injured yearly 2005-9 chartIn sum, the aggregate numbers for 2005-2009 show that the incidence of injury is on the march upward while fatalities are decreasing. That is even more clear when we look at total injuries and fatalities for that same period (left). Comparing the two shows the divergence.

(Note: the charted data is not to scale. The fatalities scale maxes out at 300/year while the injuries top out at 12,000/year. The mismatch is an conceit to illustration: because fatalities are only 1% of all collision reports, they would hardly register on the larger scale.)