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Driving Symptoms

The first type of evidence that will be presented to the jury by the prosecution will be the arresting officer’s observations of the defendant’s erratic or otherwise unusual driving symptoms—what attracted the officer’s attention in the first place. In the rare case where the officer witness did not observe driving, such as where there has been an accident, then that portion of the corpus delicti will be supplied by lay witnesses or by circumstantial inference.

How important are the driving symptoms in a DUI case? 

Most DUI defense attorneys would probably consider the blood-alcohol evidence to be the most critical, followed perhaps by field sobriety tests. But many experienced prosecutors believe that the most important area in obtaining a conviction is police testimony concerning the defendant’s driving.

A manual prepared by one of the largest prosecuting agencies in California recognizes four major categories of evidence: driving symptoms; appearance and demeanor; FSTs; and blood-alcohol test or refusal. Of these, the manual states, driving is the most important—and field sobriety tests, “which are not generally viewed by jurors as highly persuasive,” the least.

While the author does not necessarily agree with this view, it may be helpful to understand what the view of one’s opponent may be.

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How does the DUI lawyer deal with testimony of damning driving symptoms?

Typically damning testimony would involve the officer initially observing the defendant’s car traveling at a high rate of speed. For example: as the officer began pursuit, the officer noticed that the car weaved across lane lines on five occasions; at one point, the defendant failed to stop for pedestrians who were crossing in an intersection. When the officer finally decided to turn on his flashing red lights, the defendant failed to pull over for a quarter of a mile; when he did, he parked at an odd angle to the curb, the rear of his car presenting a hazard to passing traffic.

 Each case is different, of course, but engaging in a frontal attack on the officer is rarely productive—to premise a defense on the sole theory that the officer is a liar and is trying to hang your client for some unknown reason. The usually more effective approach is to take each observation, one at a time, and suggest reasonable explanations for the observed conduct—and thus, a reasonable explanation for why the officer believed (mistakenly) that the client was intoxicated.

DUI Driving Symptoms

The following list of DUI driving symptoms, from a publication issued by the National Highway Traffic Safety Administration (DOT HS-805-711), is widely used in training officers to detect drunk drivers on the roads.  After each symptom is a percentage figure which, according to NHTSA, indicates the chances that a driver is under the influence of alcohol.  For example, NHTSA’s research indicates that “the chances are 65 out of 100” that a driver who is straddling a center or lane marker has a blood-alcohol concentration of .10% or higher (the pre-.08% standard).

Turning with wide radius     65
Straddling center or lane marker     65
Appearing to be drunk     60
Almost striking object or vehicle     60
Weaving     60
Driving on other than designated roadway     55
Swerving     55
Slow speed (more than 10mph below limit)     50
Stopping (without cause) in traffic lane     50
Drifting     50
Following too closely     45
Tires on center or land marker     45
Braking erratically     45
Driving into opposing or crossing traffic     45
Signalling inconsistent with driving actions     40
Stopping inappropriately (other than in lane)     35
Turning abruptly or illegally     35
Accelerating or decelerating rapidly     30
Headlights off     30

Just to renforce this as a mathematical science thoroughly impressive to juries, NHTSA further claims — and officers are taught — that there is also a quick-and-easy formula for multiple symptoms:  “When two or more cues are seen, add 10 to the highest value among the cues observed”.

Of course, if these suspiciously precise figures are to be believed, then almost half of the folks who tailgate you every day are drunk — and almost half of the time you don’t brake smoothly you are, too.  Further, only 60% of drivers “appearing to be drunk” to the officer actually are. (Query:  How does a driver “appear to be drunk” to an officer following 100 feet behind? Slurred speech?  Alcohol on his breath?)  And speeding — one of the most common reasons for pulling DUI suspects over — is not even on the list. 

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Consider first the officer’s testimony that the defendant was speeding. One tactic is to ask the officer how many speeding tickets he has issued in his career—and how many of those involved drunk driving. The answer to this last question should be “none,” since an officer arresting someone for drunk driving rarely bothers to issue a speeding citation as well. But this simple line of questions presents issues which can later be developed in arguments to the jury.

  • If speeding is symptomatic of drunk driving, why has the officer never found speeding to be involved in any of his DUI arrests?
  • If speeding is not a symptom, then why was the officer attempting to present it as evidence of intoxication?
  • If the defendant was speeding, why wasn’t he cited for it?

DUI attorneys must, obviously, keep a tight rein on the officer during cross-examination and not permit the officer to offer explanations. If the subject is not explained in redirect, then the issue should be discussed during argument.

Evidence of speeding can be turned to the client’s advantage. This involved leading the DUI officer to admit that controlling a car requires more coordination and greater judgment as speed increases. Quite simply, driving a vehicle at the speed observed by the officer without having an accident requires considerably greater reflexes, coordination, and judgment than at the legal speed. Thus, the very fact of speeding without mishap is evidence of sobriety. In other words, rather than trying to prove the client was not speeding, counsel should simply accept the fact and turn it to his advantage. The natural tendency of the trial lawyer to contest everything should be overcome; the client is not on trial for speeding.

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  • Drunk Driving

    Los Angeles - 6 months jail, fine, license suspension

    Reduced to Exhibition of Speed (fine)
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    Glendale - 6 months jail, fine, license suspension.

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  • DUI & Hit-And-Run (.30%)

    Vista - 1-year jail, fine, license suspension.

    DUI Dismissed, Plea to Hit-and-Run (Fine)


The next driving symptom almost universally encountered in DUI cases is “weaving.” In fact, along with “alcoholic breath,” “thick and slurred speech,” and “bloodshot eyes,” it seems nearly a prerequisite to any arrest for drunk driving. And, without question, there are officers who will add these symptoms to their reports to create the classic DUI scenario. In most cases, however, the officer is honest—but guilty of suggestive perception: once he has decided that the suspect is possibly under the influence, he expects to see the usual symptoms —and normal inattentive driving becomes “weaving.”

DUI lawyers must develop through cross-examination of the officer that weaving is not nearly as unusual or symptomatic of intoxication as it sounds. The officer should be led to admit that no driver steers a car in a geometrically straight line dead center in the lane; only railroad cars travel perfectly straight. During argument, the jurors should be reminded that even the most sober of them will find that as one drives, one is constantly, perhaps subconsciously, correcting course with a back-and-forth steering wheel motion. So it is a matter of degree—and of the car's mechanical condition.

The mechanical condition of the client’s car at the time of arrest should not be overlooked in preparing for trial. A thorough inspection by a licensed mechanic may well produce a valuable defense witness, since mechanical problems can cause weaving and other erratic driving symptoms. Testimony that the car had bent tie rods, a sticking accelerator, defective suspension, worn brakes, faulty steering, improperly inflated tires, or poor wheel alignment, can be effective. Even without such a witness, the possibility of such mechanical problems can be brought out in cross-examination of the officer.

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Defendant’s Failure to
Pull Over

The officer’s next observation may involve the client’s failure to pull over after the siren or flashing red lights were activated. Once again, the tactic of the DUI lawyer is not to disprove that this happened, but rather to offer a reasonable explanation. For example, it is not unusual, and thus not evidence of inebriation, to be unaware of flashing lights to the rear, particularly during daylight hours. If the client saw the lights, they may have assumed that they were intended for someone else — not an unreasonable assumption for someone who believes they have done nothing wrong. Or the client may have reasonably believed that it was an emergency and they were to get out of the way (which the officer will see as more weaving or an unsafe lane change). If the siren was then used, counsel should develop the increasingly common problem familiar to officers, firefighters, and ambulance drivers, of motorists being oblivious to sirens because of air conditioning and car stereo systems. With the windows rolled up, the air conditioner on and the stereo blaring through large door-mounted speakers, it is hardly a surprise that many drivers do not hear sirens.

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Manner of Pulling Over

The DUI officer may testify that when the client did finally pull over, the client parked at a dangerous angle to the curb—indicating the poor judgment and coordination of the drunk driver. It can also indicate, however, a very nervous and frightened driver. The officer should be asked if they have observed this type of parking in cases involving routine traffic citations and if it is common for drivers who are pulled over to be flustered and apprehensive. With blood pressure rising and adrenaline pumping, totally sober drivers have been known to cause traffic accidents under such circumstances. If the officer chooses to deny this, jurors who have been pulled over may begin to doubt his entire testimony; few jurors would react coolly and dispassionately to being pulled out of traffic with flashing lights and sirens.

The DUI attorney should not limit the inquiry to what the officer has testified they observed: counsel should also bring out what the officer did not observe. Some experience with DUI cases is helpful here. The officer can be asked if alternately speeding up and then slowing down can be a symptom of drunk driving — or, in the alternative, if the officer has seen such driving in past DUI cases. If so, did the officer observe this type of driving with the defendant? Was the defendant going off on the shoulder of the road? Was the defendant obstructing traffic by traveling too slowly? Did the defendant run any red lights? Did the defendant cause any other cars to swerve to avoid them? What the officer did not observe can be as relevant to the issue of inebriation as what the officer did observe.

The Law Offices Of Taylor & Taylor is here to help. Call (562) 330-4173or contact us online today if you have any further questions about driving symptoms as they relate to DUI.

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