Most rear-end accidents are caused by tailgating. To avoid tailgating, the 2009 California Driver Handbook recommends that drivers use the "three-second rule." 

What's the three-second rule? When the vehicle ahead of you passes a certain point such as a sign, count "one-thousand-one, one-thousand-­two, one-thousand-three." This takes about three seconds. If you pass the same point before you finish counting, you are following too closely. 

According to the handbook, you should allow a four-second or more cushion when: 

• Being crowded by a tailgater. Allow extra room ahead. Then, if you need to, you can slow down gradually and avoid braking suddenly - and being hit from behind by the tailgater.

• Driving on slippery roads.

• Following motorcyclists on wet or icy roads, on metal surfaces (i.e., bridge gratings, railroad tracks, etc.), and on gravel. Mo­torcyclists can fall more often on these surfaces.

• The driver behind you wants to pass. Allow room in front of your car so the driver will have space to move into.

• Towing a trailer or carrying a heavy load. The extra weight makes it harder to stop.

• Following large vehicles that block your view ahead. The extra space allows you to see around the vehicle.

• You see a bus, school bus, or a placarded vehicle at railroad crossings. These vehicles must stop at railroad crossings, so slow down early and allow plenty of room.

• Merging on to a freeway.  

If you follow too closely and another driver "cuts" in front of you, just take your foot off the gas. This gives you space between your car and the other driver, without having to slam on your brakes or swerve into another lane.