Risk Factors

Risk factors that can lead to Drowsy Driving Crashes

(A) Sleep Loss



Acute Sleep Loss - the loss of even one night of sleep may cause acute sleep loss ( ie; occasional sleep loss )

Chronic Sleep Loss - whereas there are those who suffer chronic sleep loss ( ie; routine sleep loss ).

The combination of a lifestyle pattern with situational acute loss greatly increases the risk of a drowsy-driving crash.

Sleep deprivation can be due to one or more of the following;

(i) Poor quality sleep. Lack of quality sleep is the primary cause of drowsy driving.

(ii) Work-responsibilities, commitments and demands, working shift work, overtime or rotating shifts, working long hours, more than one job, working extended shifts (day plus evening plus night)

(iii) Family, childcare, or family responsibilities

(iv) Sport and leisure commitments

(v) Education - schooling, study, combining work and education

(vi) Socialising

(vii) Preparing for a trip or vacation (eg; packing bags)

(viii) Busy lifestyle, lifestyle patterns

(ix) Economic pressures

(x) Personal demands

(xi) "Pulling all-nighters" (eg; study, partying, sex)

(xii) Noisy neighbourhood

(xiii) Uncomfortable sleeping environment

(B) Driving Patterns / Time of Day



' The number one indicator of a drowsy-driving crash '.

Driving through the night (midnight and 6am), midafternoon or when you would normally be asleep.

Everyone feels tired during the circadian dip time of mid afternoon even if they are not suffering from sleep deprivation

Make sure that you are fully awake before driving first thing in the morning. (eg; going to work)

Driving a large number of miles or hours on a regular basis

"If you routinely nap during the mid-afternoon, best to avoid driving during that time" !

(C) Driving Without Proper Rest Breaks



Driving for longer times without having regular breaks. Have a rest break from driving every two hours or 100km as a minimum requirement, for a minimum of twenty minutes but if you also feel drowsy you should also have a sleep.Driving for long distances can make you fatigued which can bring out drowsiness.

(D) Undiagnosed or Untreated Sleep Disorders



  • Insomnia
  • Sleep apneoa
  • Narcolepsy
  • Restless legs syndrome
  • Snoring
  • Night terrors
  • Sleep walking


If you suffer any form of excessive day time sleepiness or suspect that you have a sleep medical condition, consult a sleep specialist as soon as possible for diagnosis and treatment.

(E) Consumption of Alcohol



  • Alcohol interacts with and adds to drowsiness.
  • Researchers have shown that sleepiness and alcohol interact, with sleep restriction excerbating the sedating effects of alcohol and the combination adversely affecting psychomotor skills to an extent greater than that or sleepiness or alcohol alone
  • Research has shown that on four hours sleep, one bottle of beer has the same effect on a drivers control and reaction as a six-pack of beer. Even one drink can make you feel drowsy


(F) Use of Sedating Medications



  • Certain medications increase the risk of drowsy-driving crashes. The risks are greater with higher drug doses and for people taking more than one sedating drug simultaneously. Check medications with your Doctor or Pharmacist in case they make you feel drowsy.
    Any medication or drug that affects the central nervous system has the potential to impair drivers
  • An entire website/campaign supporting the strong connection between drowsy driving crashes on New Zealand roads. Click on the web address to view www.candor.org.nz


(G) Sleeping Passengers



  • Do not allow passengers to sleep in the front seat. If travelling with others always, make sure that someone else is awake to keep a watch on the driver.


(H) Sounds



  • Monotonous sounds such as air-conditioning can have a hypnotic effect.


(I) Boredom



  • Driving alone, or on a long, rural, dark or boring road. Boring, monotonous scenery or comfortable, monotonous driving environment (such as straight roads) can contribute to "highway hypnosis" - as can dull scenery, and repetitive patterns such as headlights, trees, utility poles and highway markings. "Highway hypnosis" is a trance-like condition that dulls the senses, affects judgement and reduces reaction time.


(J) Consumption of a Meal and Foods under certain conditions



  • Eat properly. Don't overeat, but don't eat too little either. Eating foods high in sugar and fat (eg; hamburgers, chips, chicken) could increase the risk of a crash.
  • Read about Tryptophan, Carbohydrate chemistry and Turkey - Cheese, Pork, Chicken.www.chemistry.about.com
  • British Cheese Board Study on Cheese (pending delivery of study)


(K) Drinks



  • Soft drinks may make you bloated and uncomfortable.


(L) Certain Relaxing Music



  • Can in fact distract drowsy drivers.


(M) Illness



  • Perhaps you are recovering from surgery or a visit to the dentist.


(N) Emotional Stress



  • Significant life stresses - perhaps you are travelling to or from a funeral following the death of a loved one, visiting family members or visiting your in-laws. Job loss/ change or moving house. If so, best not to drive. ' Emotional blackmail can drawn peoples energy and make drivers feel very tired '.


(O) Sunglare



  • Eyestrain can be a major factor contributing to drowsiness.


(P) Overheated Vehicle



  • A factor leading to increased drowsiness


(Q) High Temperatures



  • Vehicles should not be allowed to overheat making it uncomfortable for the driver.


(R) High Humidity



  • As the humidity becomes high, the body's ability to sweat decreases and the heat is retained in the body.


(S) Cold Temperatures



  • Vehicles should not be allowed to get too cold making it uncomfortable for the driver.


(T) Air-conditioning



  • Too high
  • Noisy (humming)
  • Faulty (eg; heat on all the time)


(U) Vibrating Vehicle



  • Vibrations can cause stress and make you feel tired.


(V) Seating



  • The high interior comfort level of cars (eg comfortable seating), cruise control and good road engineering can lead to reduced vigilance.
  • Sitting still for periods of time can impact on the driver.


(W) Stale Air



(X) Party Drugs



  • An entire website/campaign supporting the strong connection between drowsy driving crashes on New Zealand roads. Click on the web address to view www.candor.org.nz


(Y) Smells



  • Men's Life magazine reports that the popular smell of new cars can actually be dangerous. The scent people have tried to bottle and sell to create that "new car" feeling has a dangerous sleep-inducing effect.

    'The main components in 'new car smell' are volatile organic compounds (VOC's) - gases given off by the various chemicals that glue together a car's vinyl and plastic components. Researchers Steven Brown and Min Cheng at Australia's Commonwealth Scientific and Research Organisation (C.S.I.R.O.) studied three new 1998 vehicles using a gas chromatograph. They found concentrations of VOC s as high as 64 milligrams per cubic metre. Concentrations above 10 milligrams per cubic metre are believed likely to cause short-term health effects, such as headache and nausea, and possibly long term effects, such as cancer.
    Source: National Sleep Foundation Magazine, Volume 1


(Z) Carbon Monoxide Poisoning



  • Carbon Monoxide is a colourless, odourless, highly poisonous gas that is produced by incomplete combustion. It is found in exhaust fumes, heating systems and fires etc.
  • The symptoms of Carbon Monoxide poisoning in order of increasing severity include: headache, shortness of breath, dizziness, fatigue, mental confusion and difficulty thinking , loss of fine hand-eye coordination ,nausea and vomiting, rapid heart rate ,hallucinations ,inability to execute voluntary movements accurately , collapse , lowered body temperature (hypothermia) ,coma ,convulsions ,seriously low blood pressure , cardiac and respiratory failure, death.
    'Check and repair car exhaust system leaks!'
    'Family Warns Motorists of Carbon Monoxide' poisonous gas nearly killed 2 year old girl'.
    The Decatur Daily News - www.decaturdaily.com
    The above factors (A) - (Z) have potential cumulative effects. Any single list item or a combination of them substantially increases the risk of having a drowsy drivng crash