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The next time you are driving, count how many times your fellow drivers fail to use their turn signals. Chances are you will run out of fingers and toes before the engine is warm.

Nearly half of all drivers either don't signal to change lanes or fail to turn the indicator off if they do, according to a newly released report from the Society of Automotive Engineers. Researchers observed 12,000 cars and found a failure rate on lane changes of 48%. One driver in four failed to use a signal to make a turn, the report says.

Those findings back up a 2006 survey conducted by Response Insurance in which 57% of American drivers admitted not using turn signals when changing lanes. Among drivers ages 18 to 24, 71% said they don't use their signals.

Even more disturbing than the statistics were the reasons. Forty-two percent of the signal-avoiders said they didn't have time; 23% admitted they were just too lazy.

Perhaps the rest ran out of blinker fluid. But that momentary lapse comes back to haunt many drivers.

"All drivers have an ongoing duty" to use signals, says SAE report author Richard Ponziani, "just as they have a duty to stop at a stop sign or at a red light."

While failure to signal may seem like a small infraction, improper turning and lane changing (the most frequent infractions associated with failure to signal) cause a lot of car accidents. In New York's most recent tally of accidents, unsafe lane changes were the fifth-most-common cause of accidents, and turning improperly was No. 7.

Nationwide, neglected or improper turn signals cause 2 million car accidents a year, Ponziani says. And for drivers involved in those accidents, a citation for failure to use turn signals could make the difference between a covered repair and a denied claim.

What is the law?

All states require drivers to use directional signals to indicate their intention to turn, change lanes or pass a vehicle.

The details differ, but the goal is the same: No surprises. Indicators make your fellow drivers aware of your intentions and give them enough time to adapt or respond. While the penalty varies by state, failure to signal is usually a minor traffic violation.

According to Penny Gusner, the consumer analyst at CarInsurance.com, a failure-to-signal citation could affect your insurance in several ways.

Many states do not allow insurers to raise rates for just one ticket, but a failure-to-signal citation could cost you a good-driver discount. That could bump up your premiums by as much as 25%, Gusner says. If your state does allow insurers to ding you for a single moving violation, look for a rate increase in the 5% to 20% range.

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But the real cost comes if you're involved in an accident. Comparative negligence laws allow insurance companies to reduce claims proportional to degree of fault, Gusner says. If failing to signal puts you more than 50% at fault for the accident, your claim can be adjusted downward or denied altogether, Gusner says.

And contributory negligence states -- Alabama, Maryland, North Carolina and the District of Columbia -- prohibit a driver from recovering any damages if found even a small amount at fault for the accident.

Failure to signal would certainly qualify.

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Enforcement is sporadic

The enforcement of failure-to-signal violations varies by state, and most police departments do not track or publish statistics on how many tickets are written each year.

For example, California law requires drivers to use a turn signal 100 feet before an intersection. But according to Lt. David Gilmore of the San Diego County Sheriff's Department, that limit is rarely enforced.

In many jurisdictions a failure-to-signal citation is written only if an improper turn results in an accident.

Instead, failure to signal is often a handy tool for police to establish a valid reason to pull over a vehicle that they think is suspicious. A signal violation is a primary offense -- one that legally allows a traffic stop. Police might suspect a driver is drunk, transporting drugs or guilty of any number of other infractions.

That practice can be controversial.

Florida attorney Shane Fischer says that in his experience, failure-to-signal tickets are much more common in poor, predominantly African-American or Latino communities.

Data presented in Chavez v. Illinois State Police, a class-action lawsuit, showed that Hispanics, while less than 3% of the driving-age population in one district, made up 25% of drivers pulled over in discretionary stops for offenses such as failure to signal a lane change.

A brief history of the turn signal

Before blinkers became common, drivers were required to roll down their window and stick an arm out, rain or shine, to signal their direction or a stop.

In Europe, a mechanical device known as a "trafficator," or semaphore, was used into the 1920s; mechanical arms swung out from the car's windshield pillars or doors to indicate direction.

Buick was the first automaker to offer factory-installed turn signals. Its 1939 models featured the "Flash-Way Directional Signal" only on the rear lights. The 1940 models added front indicators and a self-canceling mechanism.

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In the seven decades since, the technology hasn't changed much. Turn signals became standard equipment on most cars during the 1960s. In 1968, the federal government required that front turn signals have an amber-colored lens while the rear could be either red or amber. Those standards still exist.

Ponziani's RLP Engineering group has proposed a "smart turn signal" that would flash a reminder if it senses turns that aren't accompanied by signals and automatically cancel a lane-change signal after a certain amount of time.

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