Although it is not uncommon to encounter bicycles while driving, many drivers give little thought to them beyond treating them as an annoyance. A bicyclist is extremely vulnerable to injury when struck by a car. It is important for cars and bicycles to respect each others' presence on the road, and to follow the rules of the road so as to avoid accidents.
While any act of driver negligence can result in an accident between a bicycle and a car, it seems that the following acts are of particular concern:
Dangerous Turning: When a bicycle is present at an intersection, drivers will often try to impatiently turn in front of the cyclist. For a left-hand turn, this can cut off the bicyclist's path and create a substantial risk of injury. For a right-hand turn, the bicyclist may be knocked over, or collide with the side of the turning vehicle. Give a bicyclist with right-of-way the time to clear the intersection before attempting a turn.
Dangerous Passing: Sometimes a driver won't give a bicycle enough space while passing, either forcing the bicyclist off of the road, or potentially striking the cyclist with the side of the car or the side-view mirror.
Disregard of Bike Paths: When there is a bicycle path along a roadway, whether on the shoulder of the road or on the sidewalk, drivers should take note of the presence of the bike path. Where drivers fail to respect the presence of a bike path, driveways and intersections become points of particular danger, as a bicyclist with the right-of-way may be cut off or struck by a driver who isn't even watching for their presence.
Opening Car Doors: Sometimes after parking a car, a motorist will open the door into the path of an oncoming bicyclist. These accidents can be particularly dangerous to cyclists, as they are often propelled over the car door. Pay attention to the presence of bicycles before opening your car door.
Overestimating Bicyclists' Braking Ability: While bicycle brakes have improved in recent years, they are nowhere near as effective as car brakes. Also, sudden braking can cause a bicylist to be carried over the handlebars of the bicycle by his own momentum. Do not assume that a bicycle is capable of a sudden stop.
Underestimating Bicycle Speed: Drivers are not used to estimating the speed of bicycles, whether they are approaching from the front or rear, and may underestimate the ability of the bicyclist to catch up with them or pass them. Thus, even knowing a bicyclist is on the road, sometimes a driver will make a turn or open a car door without giving sufficient regard to the bicyclist's speed, causing an accident.
Sometimes bicyclists argue that the rules of the road are designed for cars, and shouldn't always apply to bicycles.
Ignoring Traffic Signals - It can add a lot of effort to a bike trip to come to a full stop at an obviously empty intersection, and some bicyclists are notorious for disregarding stop signs and red lights.
Passing A Line Of Stopped Cars - If you're approaching a busy intersection, with a number of cars lined up at a light or stop sign, it can be very tempting to pass the cars on the right. This can create a significant risk of accident as the cyclist reaches the intersection, where the frontmost car makes an unexpected right turn as they attempt to pass. It is important for cyclists to pay attention to turn signals, and to take particular care that it is safe to pass a car before attempting to sneak past it on the right.
Riding At An Unsafe Speed - It can be exhilarating to reach maximum speed while going downhill, and sometimes it is refreshing to bicycle on a straight road at the maximum possible speed. But bicyclists should attempt maintain sufficient control of their bicycles such that they will be able to come to a controlled stop in the event of an emergency, and should take care that their speed is not excessive for the number of intersections in the roadway or the condition of the road. If there are roadside hazards which could cause you to lose control of your bicycle, such as poorly designed sewer grates or roadside debris, take care that you won't end up accidentally veering into traffic. Recall also that speed limits apply to bicycles as well as to cars.
Maintain Your Bicycle - Make sure that your brake pads are clean and not unduly worn. Make sure that your handebars and wheels are tightly secured. Check your chain and derailleurs to try to ensure that your chain won't come off at an inopportune moment while you are riding. And otherwise check and maintain your bicycle to ensure its safety and reliability.
The poor design of bike paths, or designation of sidewalks as "bike paths", can contribute to accidents between cars and bicycles (or bicycles and pedestrians). Both bicyclists and drivers need to exercise additional caution when a bike path along a roadway is frequently crossed by driveways, or where a bike path on the shoulder of a roadway crosses sewer grates or is littered with debris. Drivers should exercise particular care when turning at intersections involving sidewalk bike paths, and bicyclists may have the right of way, but may be approaching out of the driver's blind spot at a high rate of speed. Bicyclists should not assume that drivers will see them or will necessarily follow the rules of the road - and when in doubt, should attempt to make eye contact with a driver before passing or cutting in front of them at a potential point of danger.
The risk of negligent or even reckless conduct by a bicyclist increases enormously when the bicyclist at issue is a child. Children don't always appreciate the risks associated with their bike riding conduct, nor do they necessarily understand either the rules of the road or the manner in which a two thousand pound vehicle can injure them in a collision. Children are also more likely to be showboating for their friends, riding without hands, or engaged in similar bicycling conduct which increases the risk of accident. Drivers should exercise particular caution when driving in the vicinity of children on bicycles.
A significant majority of permanent injuries which result from bicycle accidents are head injuries. The use of a bicycle helmet significantly reduces the risk of head injury from a bicycle accident. Modern bicycle helmets tend to be light and adequately ventilated. Helmet hair is a small price to pay to avoid a potential brain injury.