Dangerous Conduct By Cars
While any act of driver negligence can result in an accident between a bicycle and a car, 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.
Dangerous Conduct By Bicyclists
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.