How to Make a Safer Bicycle

Most serious accidents are caused by collisions with motor vehicles, and most safety research focuses on how roads can be designed to prevent these collisions. Some accidents are also caused by the rider losing control or mechanical failures of the bike.

We’re designing bikes that reduce the risk of accidents happening, and also reduce the risk of injury when accidents do occur. We need to know how collisions, loss of control and mechanical failure can best be avoided. We also need to know what else can be done to reduce the severity of injuries when accidents do happen.

Being visible to motor vehicles is extremely important. Many accidents involve bikes being hit from the side, therefore, being visible from all angles is especially important. It also seems that small and very bright lights, currently popular with many cyclists, may just dazzle and confuse drivers. It’s much better to have reflective material spread out over a large area, especially on the legs.

More specifically, we are addressing the following research questions:

What causes accidents and injuries to cyclists?

Many serious accidents are caused by collisions with motor vehicles. Cyclists tend to think they have been seen by motorists well before they have actually been seen, particularly at night (Wood et al, 2013).

Crossing intersections is particularly dangerous. Being visible from the side is therefore especially important. A study involving 16 cyclists riding instrumented bikes in Sweden indicated that the major risk to cyclists when crossing intersections was poor visibility (Dozza et al, 2014). Another study found that intersections at which all approaches are two-way and signalized, or where partial crosswalks were present, are more than twice as likely to result in a major collision (Klassen et al, 2014).

The speed of motor vehicles has been shown to increase the risk of severe injury to cyclists. However, the extent of this increase varies widely between studies. A study in the USA (Kim et al, 2007) showed that when cyclists collide with vehicles traveling at over 50 mph (80 kph) they are more than 16 times more likely to die from their injuries. When the speed is over 30 mph (48 kph) the risk is doubled. When the vehicle’s speed is less than 20 mph (32 kph) there is a greatly reduced risk of harm to the cyclist. A study in Denmark showed slightly smaller effect of road speeds, with speed limits of 50–60 km/h increasing the risk of fatalities by 21–45% while for speed limits above 70 km/h this increased to 274–326% (Kaplan et all, 2014). Surprisingly midblock collisions have been shown to be less severe on arterial roads compared to collector and local roads. This suggests that perceived safety and actual safety may not always correspond. Streets with parking on one or both sides were also found to greatly reduce the likelihood of severe collisions (Klassen et al, 2014).

It has been shown that 6 percent of crashes are caused by something being caught in the wheel and that pitch-over crashes are particularly dangerous resulting in landing on the head with load on the spine (Bretting et al, 2010).

It has been suggested that eBikes are more dangerous than regular bikes due to higher speeds, greater weight causing mounting/dismounting falls and front wheel drive causing skids (Schepers et al, 2014)

Key safety objectives for bicycle design:

  • Visibility is critical, especially from the side, see below.
  • Preventing wheels from being easily stopped. Risks include:
    • Mechanical failure of spokes
    • Impingement of body parts or foreign objects
  • Improved longitudinal stability, perhaps with increased wheelbase.
  • Removal of any parts able to puncture the body such as the end of handlebars and seat posts
How can cyclists be seen by drivers, and get them to give more room?

Fluorescent clothing is effective during the day and retroreflective is effective at night, with markers on the ankles and knees giving a huge improvement in visibility (Wood et al, 2012). This is thought to be due to humans’ high perceptual sensitivity to distinctively human patterns of joint movement. Lights may actually reduce the visibility of cyclists to other road users, perhaps by dazzling (Wood et al, 2012). It is for this reason that the EU k-mark standard for bike lights requires a clear cut off at elevations over 2.4 degrees so as not to cause glare (Cai et al, 2014), Wood et all do not mention whether the lights used in their study met this standard.

These findings suggest that, ideally, high visibility clothing should be worn. Alternating stripes of retroreflective and fluorescent material should be located at the extremities so as to maximize visibility of the cyclists’ joint movements. These might include the following:

  • Wrap around gaiters OR ankle bands OR socks OR shoes
  • Pedals
  • Handlebar ends
  • Gloves
  • Elbows and knees
  • Helmet
  • Wheels

It should be considered that cyclists may not use high visibility clothing, possibly due to fashion or convenience. Retroreflective clothing has recently become fashionable, a very positive development. For the best chance of being seen, the bike should duplicate these effects as far as possible. Studies of motorbikes suggest light configurations giving visual clues about the type of vehicle may improve visibility (Lars et al, 2012). For example a T-shape for a bike. However, the affect was very small.

One study has shown that drivers give cyclists more room if the cyclist is riding close to the edge of the road (Kay et al, 2014).

Other ideas – police warnings, camera warnings, spacing flags

Key safety objectives for bicycle design:

  • Increase the area of high visibility materials and lights, integrating with luggage and aerodynamic fairings
  • Maximise visual clues to help drivers identify a bicycle by outlining the shape of the bike and including moving parts such as wheels and pedals.
  • Ensure that lights are not dazzling
How can cyclists improve their awareness of hazards?

Riding position may affect a cyclist’s ability to observe hazards. The most aerodynamic positions for conventional bicycles direct the cyclist’s gaze towards the ground.

It has been shown in research that it is possible to design a bike light which meets the three requirements of making the bicycle visible to other road users, not causing glare and illuminating the ground ahead (Cai et al, 2014). However, currently available lights are not thought to fully meet these requirements.

Rear view mirrors are not widely used despite the instability of many cyclists when looking behind them. It is notable that mirrors are a standard feature on motorcycles.

More hi-tech solutions involve smart vehicles sensing, and communicating with, each other. At its simplest, this could involve a motion sensor at the rear of a bicycle which some alert to the cyclist when vehicles are approaching. Tome Software, Trek Bicycles, Ford Motor Company and the University of Michigan are developing open bicycle-to-vehicle (B2V) and Cellular Vehicle-to-Everything (C-V2X) communication protocols. The technology is intended to be open so that other manufacturers can use it in devices such as lights, helmets and cycle computers. A study has shown that it is possible to use traffic monitoring cameras to identify when bicycles are in dangerous situations at intersections (Detzer et al, 2014). This could be used to improve intersection designs and could also potentially communicate with smart bikes to alert the riders.

How can accidents involving loss of control be avoided?

Modern brakes, in particular disk brakes, are usually able to lock the wheels. Therefore, the minimum stopping distance is limited by skidding and avoiding pitch-over, or ‘going over the handlebars’ (Bretting et al 2010). To avoid skidding friction can be increased by using wider tires running at lower pressure. Softer rubber compounds and appropriate tread pattern will also help. To avoid pitch-over the combined center of gravity (CofG) for the cyclist and bike should be as low and far behind the front wheel as possible. This can be aided by slacker head angles and the position of loads such as luggage or batteries. Dropper posts can also help riders to shift their weight during descents. It has been suggested that stopping distances may be further reduced by using an electronic braking-pressure distribution system to optimally distribute braking force between the wheels (Lie & Sung, 2010).

Increasing fork trail, handlebar width and wheelbase all improve steering stability.

Excessive weight can also cause falls in crashes, particularly the less physically fit cyclists. This has been noticed mostly in E bikes.

Front wheel skids are more likely to result in accidents then rear wheel skids. There should be a bias towards traction of the front wheel. Front wheel drive should be avoided in E bikes as this can cause front wheel skids.

How can dangerous mechanical failure be avoided?

One study found that approximately 10 percent of injuries in children were caused by spokes and 3.6 percent by the handlebars (Kiss et al, 2010).

How can the bike structure not cause further injuries?

We’re still carrying out research into this topic but here are some intitial thoughts. This comes down to not have sharpt tubes and edges injure the cyclist in a crash. Some horrible injuries are caused by things like seat posts pushing through saddles and impailing cyclists in crashes. Careful design of failure modes under crash conditions is required, similar to what is done for cars.

How can the bike and clothing protect from injury?

We’re still carrying out research into this topic but here are some initial thoughts. Clearly helmets are what every one thinks of here and there is a lot of research showing they are effective.

Other serious injuries to vital organs and the spine may be prevented using other forms of protection. For example, the recently released Helite airbag vest.

Effect of using devices

Using devices while cycling is dangerous. Worryingly, this is actively being encouraged at the moment with handsfree systems being promoted for bicycles, for example, the Alexa-enabled E-bike.

Warning:

Using a phone hands-free has been shown to be almost as distracting as holding one.

It has been shown that using touchscreen devices is more dangerous than those with tactile buttons (De Waard et al, 2014).

Misc. Safety Info

Accident rates for cyclists

Many studies have shown that cyclists are a risk of accidents. One study found that cyclists in Tasmania, Australia, have 1.6 major accidents and 3.7 minor accidents per 100,000 km ridden (Palmer et al, 2014). Major accidents were those requiring medical attention or resulting in a day off work while minor accidents were those which affected daily activities or had a financial cost. It found that men were less likely to have minor accidents while mountain biking significantly increased the likelihood of all accidents.

Pedestrians

A study carried out in the USA indicated that the provision of cycle paths is significantly reducing the number of pedestrians injured by cyclists (Tuckel et al, 2014).

Summary of requirements

Bikes should have reliable lights which cover a large area with diffuse light to be visible to motor vehicles from any angle, a forward beam that illuminates the road surface and a vertical cut-off so as not to dazzle drivers. Ideally they should also provide visual cues by conforming to the shape of the bike and rider, and including moving parts. To be reliable and convenient such lights must be integrated into the structure of the bike and have integral charging. A helmet should have with lights which are charged when stored on the bike.

High visibility, ideally florescent, panels should make the bike visible to drivers from any angle in daylight. These should also provide visual cues by conforming to the shape of the bike and rider, and showing the movement of the bike. Wheels and pedals should be included.

Providing lights and high visibility panels over a large area may be difficult within the race-legal designs of bikes currently available. If aerodynamic fairings are present, however, these safety features may be integrated. It is important that such fairings do not lead to loss of control through oscillations caused by vortex shedding or cross wind effects.

If possible, pitch-over crashes (‘going over the handlebars’) should be prevented by lengthening wheelbase and lowering center of gravity.

E-bikes should be rear wheel drive or have traction control to prevent front wheel skids, the center of gravity should be as low as possible and overall weight should not be excessive.