As cities across the nation encourage people to ditch their cars in favor of a greener, healthier alternative, researchers are asking important safety questions about how best to incorporate bicycles into our motorized streets.
Along with pedestrians, bicyclists are known in highway safety parlance as "vulnerable road users" because, unlike vehicle occupants, they have no protective structure around them and are completely outmatched by motor vehicles in terms of mass. Cities are using a variety of approaches, including bike lanes, cycle tracks, shared lane markings, bike boulevards and bike boxes, to give bikes their own space on the road. Research points to some successes, but more study is needed to find out which of these things can entice more people onto bikes while keeping crashes down.
"Biking has obvious advantages over driving for people's health and the environment, but there's no getting around the fact that bicyclists are vulnerable," says David Zuby, the Institute's chief research officer and one of several employees who often bike to work. "If you're going to encourage biking, you have a responsibility to make it as safe as possible. At the same time, the safer it feels, the more people will be willing to give it a try."
Bicycles account for a small percentage of trips in the United States — just 1 percent in 2008, according to the National Household Travel Survey. However, biking is on the rise in some parts of the country, particularly in cities that have added bike lanes and other infrastructure in recent years. For example, in the District of Columbia, where the number of miles of bike lanes went from 2.7 in 2000 to 55.8 in 2012, more than 3 percent of residents regularly bike to work. In New York City, bicycle commuting more than doubled from 2007 to 2011, officials there say.
Compared with the total number of people who die on the nation's roads, the number of bicyclists killed in crashes with motor vehicles is tiny. A total of 675 bicyclists, or 2 percent of all traffic fatalities, were killed in 2011. That was up from 616 in 2010. It is too early to tell whether that was a one-year bump or the beginning of a longer-term trend, but if efforts to encourage biking are successful, the number of bicyclist fatalities also could be expected to rise. These statistics reflect a change in biking demographics, as adults increasingly use bicycles as a regular form of transportation. Deaths among bicyclists younger than 20 declined 87 percent from 1975 to 2011, while deaths among bicyclists 20 and older rose 167 percent. The vast majority of fatalities continue to be males.
About a quarter of fatally injured bicyclists age 16 and older have blood alcohol concentrations of 0.08 percent or higher. Impaired cycling is prohibited in some states, but little is known about whether these laws help. Whether or not the problem can be addressed directly, increased separation of bikes from traffic is arguably even more important in the case of bicyclists who have foggy judgment and slow reaction times as a result of drinking.
Fatality statistics tell only part of the story. Crashes not involving motor vehicles and those that take place in parking lots or other locations away from public roads usually aren't reported to police and aren't included in federal databases. A 1999 Federal Highway Administration study of bicyclists and pedestrians treated in emergency rooms found that 70 percent of the bicyclists had been injured in a crash not involving a motor vehicle, and 31 percent were injured in nonroadway locations. Bike-only crashes tend to be less serious than those involving vehicles, but a small number of them are fatal.
Bicyclist deaths by age and gender, 1975-2011
A lane of their own
The most common way cities accommodate bicycles is by marking off bike lanes. These lanes vary in their width, and in some cases, parked cars are located to the right of the bike lane, leaving riders vulnerable to "doorings," when doors of parked cars swing open in their path. Other common problems include bike lanes that end abruptly or contain obstacles such as sewer gratings or potholes.
"It's not enough to simply mark off a bike lane," says Allan Williams, who recently reviewed bicycle and pedestrian literature for the Institute and previously served as chief scientist. "If it's not well designed and maintained, people won't use it, and it won't ensure safer travel."
Some researchers have reported crash reductions from bike lanes, but one recent study in New York City was more mixed. The authors looked at what happened after 43 miles of bike lanes were added from 1996 to 2006, comparing crashes on the bike-lane streets with crashes on similar streets that didn't get bike lanes. They found crashes involving bicycles increased with the bike lanes but not significantly, while crashes involving only motor vehicles decreased. The authors attribute the increase in crashes with bikes to a presumed increase in bicyclist exposure, although data on that weren't available. However, in general, biking became more common during that period, according to the city's data: The number of bicyclists entering the central business district increased 51 percent from 1996 to 2006 and 48 percent from 2006 to 2008.
The increase in bicycle crashes in New York City was largest at intersections. This isn't surprising, since intersections can be tricky places for bicyclists and vehicles to avoid each other, and 36 percent of bicyclist deaths across the U.S. during 2011 occurred in one. The bike lanes in the New York study had no intersection markings. They simply stopped before an intersection and picked up again afterward.
One feature that can be added to bike lanes to improve intersection safety is the bike box. This is a special section for bikes to stop at a red light. It is usually located in front of and to the right of the vehicle stop line. Bike boxes make bicyclists more visible and allow them to go first through an intersection. A study of bike boxes in Portland, Ore., found that vehicle encroachments beyond the stop line declined and yielding behavior improved.
Some cities have installed separate traffic signals for bicyclists that give them an advance green signal, but their effect on safety isn't known
Beyond bike lanes
Cycle tracks are bike lanes that are separated from vehicle traffic by physical barriers. A study of bicyclist injuries in Toronto, Ontario, and Vancouver, British Columbia, estimated injury risk on 14 route types and found that cycle tracks had the lowest risk — about one-ninth that of major streets with parked cars and no bike infrastructure. Injury risk on major streets with bike lanes — both with and without parked cars — was lower than on the non-bike-lane streets, but higher than on cycle tracks.
BIKE BOXES, such as the one pictured above, give bicyclists their own space to stop at red lights, allowing them to clear the intersection first and minimizing conflicts.
A CYCLE TRACK, above left is a bike lane separated by a physical barrier.
SHARROWS, above right, remind road users that bicyclists can use the full lane.
Some measures are aimed at getting bicyclists and motorists to share the same space more amicably. Shared lane markings, or "sharrows," tell drivers to expect bicyclists and remind all road users that bicyclists may ride in the center of the lane. A 2011 study using video footage found that sharrows in three cities increased operating space for bicyclists and reduced sidewalk riding.
Bicycle boulevards, meanwhile, are networks of side streets that parallel major roads. These roads are used by motor vehicles but not as frequently as the main roads and are designated as preferred routes for bikes. They have pavement markings indicating their bike boulevard status and often include traffic-calming features such as speed humps and partial road closures that make it impossible for vehicles to drive the full length of the street. In Berkeley, Calif., rates of bicycle-vehicle collisions were lower on seven bicycle boulevards than on parallel urban arterials.
Such innovations clearly need to be publicized in the community if they are to work, Williams says. "When Portland introduced bike boxes, it educated bicyclists and drivers through billboards, fliers, posters and an enforcement campaign. As a result, the bike boxes were well received and understood," he says.
Not all options for improving bicyclist safety involve paint on pavement. Helmets, for instance, have been estimated to reduce the risk of head injuries to bicyclists by 85 percent, but no state requires them for adults. Such a requirement would improve safety, but some worry it would discourage biking. Only 15 percent of fatally injured bicyclists in 2011 were wearing helmets.
Twenty-one states and the District of Columbia require young bicyclists to use helmets. Helmet laws for children don't lead to increased helmet use among adults, studies show. However, one question that hasn't been answered is whether children required by law to wear helmets are more likely to wear them when they become adults.
Bicyclists can make themselves easier to spot with lights and reflective clothing. A recent study in Denmark found that daytime running lights on bikes reduced crashes by 17 percent compared with a control group. New types of lighting on vehicles and night-vision systems also could help drivers spot bicyclists and pedestrians more easily at night. A recent Highway Loss Data Institute study found that vehicles equipped with steering-responsive adaptive headlights had fewer crashes involving other vehicles, as well as a reduction in the frequency of at-fault injury claims. It is unknown how much this benefitted cyclists (see "They're working: Insurance claims data show which new technologies are preventing crashes," July 3, 2012).
Broader efforts to reduce vehicle speeds in urban areas are likely to help bicyclists, as well as pedestrians. Slowing down vehicles lessens the severity of collisions. In addition, it likely prevents some crashes by giving drivers and bicyclists more time to react and by decreasing vehicle stopping distances. Lowering speed limits, narrowing roads and installing speed cameras are all known to reduce vehicle speeds, but more research is needed into their effects on bicycle crashes.