Driving at Night and in Bad Weather, and Alcohol, Other Drugs and Driving: Headlight Range and Glare Recovery, Never Outrunning Your Lights, Parking at Night, Rain, Slippery Spots, Hydroplaning, Skids, Recovering From the Shoulder, Fog and Smoke, Flooding, Wind, Stuck Vehicles, Tornadoes, Winter Braking, ABS, How Alcohol Works, Blood Alcohol Concentration, Crash Risk by BAC, Judgment, Vision, Reaction and Alertness, Everyday Drugs, Implied Consent and No Refusal, the DUI Law and Its Penalties, Interlocks, Child Endangerment, Under-21 Laws and Prevention
Written for aiforu2 as the source for a practice-test bank and the on-device tutor for the Tennessee driver license knowledge test. The facts follow the official manual; the wording is ours.
Source: Tennessee Comprehensive Driver License Manual (TDOSHS, July 2022 information), Section B chapter 6 "Driving at Night and in Inclement Weather Conditions" (pages 74–78) and chapter 7 "Alcohol, Other Drugs and Driving" (pages 79–84).
Night driving
More deaths happen at night than by day, most on Friday and Saturday nights, because reduced vision impairs depth perception, color recognition and peripheral vision. The law requires headlights that show a person 200 feet ahead, properly aimed with clean lenses and windshield. The basic rule is never outrun your headlights: keep your stopping distance shorter than your sight distance, slow for conditions, look beyond the beams for dark shapes, glance to the sides for the pavement edge, avoid looking into oncoming lights by steering with the right edge or white line, and do not flash your high beams at an offender. Oncoming glare contracts the pupils, and glare recovery leaves you nearly blind for a moment, worse for older drivers. Dim within 500 feet when meeting or overtaking, always use low beams in town, and avoid blasting oncoming cars on right-hand curves. Aim the headlights correctly. When parked at night, never leave the headlights on, but leave the emergency and parking lights on; parking on an interstate shoulder or ramp is prohibited except for a disabled vehicle.
Rain and slippery roads
Wet pavement can be as treacherous as ice: slow down, allow more stopping distance and expect skids in sharp turns. Roads are slickest when rain first begins, as dirt and oil form a greasy film, so slow at the first drops; wait a few seconds before starting the wipers. Rain calls for lower speed, low-beam headlights (required by law in daytime rain, fog or snow), wipers and defroster, early signals and early braking. Shade from trees and buildings hides ice on cold wet days; bridges and overpasses freeze before the road; hot pavement is very slippery in the first minutes of rain; and near freezing the road may be slicker than at colder temperatures. Hydroplaning can lift the tires off the road in heavy rain; a gust or a slight steering change can spin the car, stopping distance may triple, and it can happen at any speed. Ease off the gas, never slam the brakes. In a skid, the wheels no longer roll and you have no control: stay off the brake, steer in the direction you want to go (if the rear slides left, steer left), turn back as the car straightens so it does not skid the other way, and keep correcting. If your wheels drop off the pavement, lift off the gas without braking, hold the wheel firmly without jerking, brake lightly and briefly, keep the car straight, and steer back on only when no cars are near and you have slowed. Rumble stripes on the edge line improve wet-night visibility and warn by vibration.
Fog, smoke, flooding, wind and storms
The best advice for fog or smoke, common with Tennessee's forest fires and temperature swings, is not to drive. If you must, use low beams only (high beams reflect into your eyes, and parking or fog lights alone are illegal), slow down, avoid crossing traffic, keep the radio down and the phone off, use wipers and defroster, stay right, avoid passing, and never stop on the road; if you cannot see the edge, pull far right and use the flashers, and leave a stalled vehicle. Flooding kills more people than any other thunderstorm hazard: six inches of moving water can knock a person down, 6 to 12 inches can take control of a car, most cars float in 18 to 24 inches, and two feet carries them away. Turn around, don't drown: never drive through floodwater, and if the car stalls, leave it for higher ground. Ignoring flood barricades can be charged as reckless driving with restitution for the rescue. Wind is dangerous for campers, RVs, trailers and light cars: slow down, expect gusts leaving sheltered areas and when meeting trucks, move right and slow when a truck passes, and expect a headwind to demand more throttle and a tailwind earlier braking. Sunglasses, clean windows and visors cut sun glare, and with the sun behind you, oncoming drivers may not see your signals. Stuck in mud or snow, use low gear with straight wheels, gentle throttle and no spinning, rock forward and backward, and place boards under the tires only with the car out of gear; carry chains and fit them at the far right of the road before snow or mud. In a tornado do not try to outrun it: leave the car, lie face down in a ditch. In hail or sleet, shelter under an overpass.
Winter driving
The three big errors on snow and ice are overpowering and spinning the wheels, overbraking and sliding them, and oversteering and skidding. Clear all glass and lights, carry a scraper and brush, use headlights in poor visibility, start slowly, keep a steady moderate speed, use momentum in deep snow, and fit snow tires. Low traction can stretch a stop from 20 mph to 200 feet or more. Brake gently to just short of lockup and ease off slightly if the wheels lock, without pumping; continuous hard braking locks the front wheels and takes away steering. With ABS, apply constant firm pressure all the way to the floor. Sunny hillsides may be wet while shady sides are iced, bridges ice first, and stop-and-go traffic packs snow into a slick surface.
How alcohol affects you
By law at least 25 percent of knowledge test questions cover this topic. Between 10 p.m. and 2 a.m. one driver in ten is intoxicated, and nearly half of DUI arrests are social drinkers. Alcohol enters the blood within one to two minutes; the liver oxidizes about one drink per hour, and coffee, exercise or a cold shower cannot speed it up, so only time sobers you. BAC is the percentage of alcohol in the blood, and .08 is always illegal; it rises with the number of drinks per hour regardless of your weight or the drink type, faster for lighter people, people with more body fat (alcohol dissolves in water, not fat), and people drinking on an empty stomach. At .10 you are seven times more likely to cause a crash, at .15 25 times, and at .17 50 times; a 12-ounce beer holds about the alcohol of a one-ounce shot, and one drink within 15 minutes already brings stiff penalties at .02 for drivers under 21. The first thing alcohol affects is judgment, then vision: night vision drops by more than half, glare recovery slows, side vision falls about 30 percent at .05, and depth perception suffers because each eye sees a slightly different picture, while the eyes supply about 90 percent of driving information. Reaction time and coordination are impaired from .02, and alertness fades because alcohol is a depressant; the "stimulation" is only lost inhibition. Two or three drinks in three hours impair most people, and driving skills are measurably worse at .03 to .04. Mixing alcohol with tranquilizers, sedatives or even cold remedies multiplies the effect; a prescription is no defense.
The DUI law
Under implied consent, driving in Tennessee means consenting to a blood or breath test when an officer has reasonable grounds; refusing after arrest typically brings a 12-month court suspension, and the 2012 No Refusal law lets officers seek warrants for blood samples. It is unlawful to drive or be in physical control of a vehicle on any public road or on shopping center, trailer park or apartment premises while under the influence of any intoxicant, marijuana, narcotic or stimulant drug, or with a BAC of .08 or higher; a driver can be convicted at .00 on impairment evidence, and drug penalties equal alcohol penalties. Penalties: a first conviction brings 48 hours in jail (7 days at .20 or more), a $350 to $1,500 fine and a one-year revocation; a second, 45 days to 11 months 29 days, $600 to $3,500, two years and vehicle seizure; a third, 120 days to 11 months 29 days, $1,100 to $10,000, 3 to 10 years and seizure; a fourth or later is a Class E felony with at least 150 days, $3,000 to $15,000 and revocation from five years to indefinite. Judges also order treatment assessment, DUI school or rehabilitation, restitution, and litter pickup for three eight-hour shifts in a vest reading "I am a DRUNK DRIVER"; an ID issued during revocation is marked DUI offender. A vehicle is seized for driving on a DUI revocation or for two DUIs within five years; restricted licenses may require an ignition interlock for six months to a year on a first offense, up to three years on a second and up to ten years afterward, and two DUIs in five years mean an interlock for six months after reinstatement. DUI with a child under 18 adds a mandatory 30 days in jail and a $1,000 fine, becoming a Class D felony for serious injury and a Class C felony for death; a crash killing someone can bring a vehicular homicide charge and injuring someone aggravated assault. A DUI also costs bond, lawyers, lost work, courses and insurance.
Young drivers and prevention
Crashes are the leading killer of young people and nearly half are alcohol related; teens are impaired at low BAC and crash more often between .01 and .08 than older drivers. Ages 18 to 20 convicted of buying, trying to buy or possessing alcohol lose the license for one year, then two, even off the road. Juveniles 13 to 17 who possess, consume or sell alcohol or drugs are suspended for one year or until 17, whichever is longer, then two years or until 18. A driver 16 to 20 with a BAC of .02 or under any influence commits underage driving while impaired: one year of suspension, a $250 fine and possibly public service. Decide before drinking that you will not drive, use a designated driver, ride with a sober friend, hand over your keys, and say "No thanks, I'm driving." In 2020, 27 percent of Tennessee traffic deaths were alcohol related, and in 2021 about 41 percent involved an impaired driver.
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