The National Highway Traffic Safety Administration (NHTSA) estimated that in 2003, about 36 percent of motorcycle operators involved in fatal crashes had BAC of 0.01 or higher.

Clearly, enforcing impaired driving laws is a key to reducing the number of alcohol-related motorcyclist fatalities. But which clues should be used to detect im­paired motorcyclists?

NHTSA sponsored research to develop a set of be­havioral cues to be used by law enforcement person­nel to detect motorcyclists who are operating their vehicles while intoxicated. The researchers began by interviewing experienced patrol officers from across the country to determine what behavioral cues have been used to detect impaired motorcyclists. A few, primarily motorcycle officers, suggested cues that re­flected considerable understanding of the mental and physical requirements of riding a motorcycle. Others believed the cues to be identical to those used to de­tect impaired drivers. But some officers, even those with many years of experience, reported they believe there are no cues that can be used to distinguish DWI from unimpaired motorcycle operation.

In addition to interviewing law enforcement person­nel, the research team developed a database of 1,000 motorcycle DWI arrest reports. The research team focused on officers’ narratives and motorcyclists’ behaviors that motivated the stops, and correlated those behaviors with blood alcohol concentrations (BAC). Analysis of the interviews and arrest report data resulted in an inventory of about 100 cues that have been observed by officers in relation to impaired operation of motorcycles.

The researchers, working closely with law enforce­ment personnel, conducted two major field studies involving more than 50 sites throughout the United States. Officers recorded information about every enforcement stop they made of a motorcyclist. Those field studies permitted the researchers to identify the most effective cues and to calculate the probabilities those cues were predictive of DWI. This brochure highlights the results of that research.

Fourteen cues were identified that best discrimi­nate between DWI and unimpaired motorcycle op­eration. These cues have been labeled as “Excellent Predictors” and “Good Predictors,” based on the study’s results. The excellent cues predicted im­paired motorcycle operation at least 50 percent of the time. The good cues predicted impaired motor­cycle operation 30 to 49 percent of the time. The special coordination and balance requirements of riding a two-wheeled vehicle provided most of the behaviors in the “Excellent” category of cues.

Important Information

Law enforcement officers across the United States have used the cues described in this brochure to help detect impaired motorcycle operators. The cues can be used at any hour of the day and night, and they apply to all two-wheeled motor vehicles.

The cues described and illustrated in this brochure (and on a training video) are the behaviors that are most likely to discriminate between impaired and normal operation of a motorcycle. Cases that involve speeding, however, require additional clarification. Motorcyclists stopped for excessive speed are likely to be driving while intoxicated only about 10 per­cent of the time (i.e., 10 times out of 100 stops for speeding). But because motorcyclists tend to travel in excess of posted speed limits, speeding is associ­ated with a large portion of all motorcycle DWI ar­rests. In other words, while only a small proportion of speeding motorcyclists are likely to be considered DWI, the large number of motorcyclists who are speeding results in a large number of DWIs, despite the relatively small probability.

This research will be helpful to officers in:

.                      ■ Detecting impaired motorcyclists

.                      ■ Articulating observed behaviors on arrest reports

.                      ■ Supporting officer’s expert testimony

Drifting During Turn or Curve

Earlier studies have shown that the most common cause of single-vehicle, fatal motorcycle crashes is the failure to negotiate curves, with the motorcycle continuing in a straight line until it strikes a station­ary object. This type of crash is usually caused by alcohol-impaired balance and coordination. In less extreme cases, the motorcycle’s turn radius expands during the maneuver. The motorcycle appears to drift outside of the lane or into another lane, through the curve, or while turning a corner. If you see a motor­cycle drifting during a turn or curve, do the rider a favor and pull him or her over – our study showed there is a better than average possibility that the mo­

Trouble with Dismount

Parking and dismounting a motorcycle can be a useful field sobriety test. The motorcyclist must turn off the engine and locate and deploy the kick­stand. The operator must then balance his or her weight on one foot while swinging the other foot over the seat to dismount. But first, the operator must decide upon a safe place to stop the bike. Problems with any step in this sequence can be evidence of alcohol impairment.

Not every motorcyclist you observe experiencing some difficulty with a dismount is riding under the influence, but study results indicated that more than 50 percent of them were DUI offenders. In other words, having a problem dismounting is a reliable cue to DWI.

Trouble with Balance at Stop

One typical practice for motorcycle riders at a stop is for the motorcyclist to place one foot on the ground to keep the bike upright, while leaving the other foot covering the brake pedal. Some riders favor placing both feet on the ground for stability. Riders whose balance has been impaired by alcohol often have difficulty with these tasks. They might be observed as having shifted their weight from side-to-side, that is, from one foot to another, to maintain balance at a stop. From a block away, an officer might notice a single taillight moving from side to side in a gentle rocking motion. If you observe a motorcyclist having trouble with balance at a stop, there is a better than average chance that the operator is a DWI offender.

Turning Problems

The research also identified four turning problems that indicate rider impairment:

■     Unsteady During Turn or Curve. The gy­roscopic effects of a motorcycle’s wheels tend to keep a motorcycle “on track” as long as speed is maintained. As a motorcycle’s speed decreases, the demands placed on the operator’s balancing capabilities increases. As a result, an officer might observe a motorcycle’s front wheels or handlebars wobbling as an impaired rider attempts to main­tain balance at slow speeds or during a turn.

■       Late Braking During Turn. The next turn­ing problem is “late braking during a turn or on a curve.” A motorcyclist normally brakes prior to entering a turn or curve, so the motorcycle can accelerate through the maneuver for maximum control. An impaired motorcyclist might mis­judge the speed or distance to the corner or curve, requiring an application of the brakes during the maneuver.

■     third turning problem occurs when a motorcyclist normally negotiates a turn or curve by leaning into the turn. When a rider’s balance or speed decision-making is impaired, however, the rider frequently attempts to sit upright through the maneuver. As a result, a trained observer can detect an “improper

■    Erratic Movements During Turn. The fourth turning problem is “erratic movements.” These are defined as an inconsistent action or a sudden cor­rection of a motorcycle maneuver during a turn or curve that can also indicate impaired driving. If you observe a motorcyclist who is unsteady during a turn or curve, brakes late, assumes an improper lean angle, or makes erratic movements during a turn or curve, there is a better-than-average chance that the motorcyclist is driving while impaired.

A vigilance problem also is evident when mo­torcyclists are inattentive to their surroundings or are seemingly unconcerned with detection by law enforcement. For example, there is cause for suspicion of DWI when a motorcyclist fails to periodically scan the area around the bike when in traffic, a wise defensive riding measure to guard against potential encroachment by other vehicles. There is further evidence of impairment if a mo­torcyclist fails to respond to an officer’s emergency lights or hand signals.

If you observe a motorcyclist to be inattentive to the surroundings, there is a better than average chance that the motorcyclist is a DWI violator.

Inappropriate or Unusual Behavior

There is a category of cues referred to as “inappro­priate or unusual behavior.” This category of cues includes behaviors such as operating a motorcycle while holding an object in one hand or under an arm, carrying an open container of alcohol, dropping something from a moving motorcycle, urinating at the roadside, arguing with another motorist, or oth­erwise being disorderly. If you observe inappropriate or unusual behavior by a motorcyclist, there is a bet­ter than average chance that the motorcyclist also is a DWI offender.

Weaving

You are probably familiar with weaving as a predic­tor of DWI. If you see an automobile weaving there is a better than average chance the driver has ex­ceeded the legal alcohol limits, but if you observe a motorcycle to be weaving, the probability of DWI is even greater – weaving is an excellent cue. Weaving involves excessive movement within a lane or across lane lines, but does not include movements neces­sary to avoid road hazards.

Erratic Movements While Going Straight

If you observe a motorcyclist making erratic move­ments or sudden corrections while attempting to ride in a straight line, study results indicated there is a good probability that the rider is a DWI violator. In fact, during the study erratic movements while going straight were observed 30 to 49 percent of the time in relation to impaired driving.

Operating without Lights at Night

Operating a motorcycle without lights at night is dangerous and can be another indicator of operator impairment. Study results showed that if you detect a motorcyclist riding at night without lights, there is

Motorcyclists tend to ride faster than automobiles so speeding is not necessarily a good predictor of DWI for motorcyclists. On the other hand, recklessness or riding too fast for the conditions was found to be a good indicator of operator impairment.

Following Too Closely

Following too closely, which is an unsafe following distance, is another indication of impaired operator judgment. During the study, this cue was found to be a good predictor of DWI by motorcycle riders.

Running Stop Light or Sign

Failure to stop at a red light or stop sign can indicate either impaired vigilance capabilities (i.e., did not see the stop light or sign, or officer), or impaired judg­ment (i.e., decided not to stop). Whatever the form of impairment, if you observe a motorcyclist running a stop light or sign, there is a good chance that he or she is a DWI offender.

Evasion

Evasion, or fleeing an officer, is a recurring problem. If a motorcyclist attempts to evade an officer’s en­forcement stop, study results indicate there is a good chance he is a DWI violator as well.

Wrong Way

Obviously, riding into opposing traffic is dangerous. Study results showed that when you find a motor­cycle going the wrong way in traffic, there is a good chance that the operator is under the influence. This includes going the wrong way on a one-way street, and crossing a center divider line to ride into oppos­ing traffic.

This brochure and related training materials are based on NHTSA Technical Report DOT HS 807 839, The Detection of DWI Motorcyclists,which is available upon request from NHTSA’s Safety Countermeasures Division (NTI-121), 400 Seventh Street S.W., Washington, DC 20590.