Aరహదారి roadమీద user'sవాహనాలు capabilityనడిపే isవ్యక్తుల affectedసామర్ధ్యం byవారి theయొక్క physicalభౌతిక andమరియు mentalమానసిక abilityస్థితిగతుల to assess conditions andమీద respondఆధారపడి quicklyఉంటుంది. Studiesపరిశోధనలు<ref name = trl0>{{cite web | url = http://www.dft.gov.uk/pgr/roadsafety/research/rsrr/theme3/ | title = Research projects, Theme 3: Impairment | edition = Policy, guidance and research | publisher = UK [[Department for Transport]] | accessdate = 2008-01-01 }} </ref> haveకొన్ని establishedముఖ్యమైన some common conditions that impair this judgment,కారణాలను includingగుర్తించాయి:
* poor [[Visualదృష్టి perception|eyesightలోపాలు]] and/or [[Disability|physical impairment]], with many jurisdictions setting simple sight tests and/or requiring appropriate vehicle modifications before being allowed to drive;
* [[వృద్ధాప్యం]] (old age]]), with some jurisdictions requiring driver retesting for reaction speed and eyesight after a certain age;
* [[అలసట]] (Fatigue)
* [[Fatigue (medical)|Fatigue]];
* excessiveఅధికంగా [[Short-term effects of alcohol|alcoholమధ్యపానం]], with simple [[Blood alcohol content|blood-alcohol]] limits enforced through drink-driving laws (although some level of impairment may occur below the legal limit). See also: [[alcohol-related traffic crashes in the United States]];
* drugకొన్ని useమందుల వాడకం - including some [[prescription drug]]s, [[over the counter drug]]s (notably [[antihistamine]]s, [[opioid]]s and [[muscarinic antagonist]]s), and [[illegal drug]]s.
