Car accidents rarely happen for just one reason. A driver may be speeding when traffic suddenly stops, become distracted while approaching an intersection, or lose control because wet pavement makes an already dangerous situation worse.
Some of the most common causes and contributing factors in car accidents involve speeding, distracted driving, impaired driving, reckless behavior, failure to obey traffic signals, unsafe lane changes, fatigue, poor visibility, hazardous road conditions, and vehicle problems.
Understanding why crashes happen can help drivers recognize dangerous situations earlier, make safer decisions behind the wheel, and better understand what may have contributed to a collision after one occurs.
Quick Takeaways
- Many crashes involve more than one contributing factor, such as speeding combined with distraction, poor visibility, or wet pavement.
- Speeding remains one of the most serious roadway safety problems. NHTSA reports that it contributed to 29% of U.S. traffic fatalities in 2024.
- Distracted driving includes far more than texting. Eating, navigation systems, passengers, phone calls, and anything else that takes a driver’s attention from the road can create a distraction.
- Alcohol and drugs can impair judgment, coordination, reaction time, and perception, significantly increasing crash risk.
- Weather and roadway conditions may contribute to a collision even when driver behavior is also involved.
- Determining why a crash occurred can be important when police, insurers, and attorneys evaluate fault and liability.
What Are the Most Common Causes of Car Accidents?
Federal traffic safety data consistently identifies behaviors such as speeding, alcohol impairment, and distracted driving as major roadway safety problems. In 2024, speeding contributed to 29% of all U.S. traffic fatalities, 11,904 people died in alcohol-impaired-driving crashes, and 3,208 people were killed in crashes involving distracted drivers.
The following are 25 common causes and contributing factors drivers should understand.
Driver Behavior and Human Error
1. Distracted Driving
Distracted driving occurs whenever something takes a driver’s eyes, hands, or attention away from driving. Cell phone use is one of the most recognizable examples, but drivers can also become distracted by passengers, food, navigation systems, entertainment controls, pets, or objects inside the vehicle.
Texting is particularly dangerous because it combines visual, manual, and cognitive distraction. NHTSA notes that reading or sending a text can take a driver’s eyes off the road for about five seconds—roughly the distance of a football field when traveling at 55 mph.
2. Speeding
Driving faster than the posted speed limit – or simply too fast for current road, traffic, or weather conditions – reduces the amount of time a driver has to recognize and react to danger.
Speed also increases stopping distance and the forces involved when a crash occurs. According to NHTSA, 11,288 people were killed in speeding-related crashes in 2024, representing 29% of all traffic fatalities.
3. Drunk Driving
Alcohol affects many of the skills necessary for safe driving, including judgment, concentration, coordination, visual perception, and reaction time.
NHTSA reports that 11,904 people died in alcohol-impaired-driving crashes in 2024, accounting for approximately 30% of U.S. traffic fatalities. Even alcohol levels below the legal limit can affect driving ability.
4. Reckless or Aggressive Driving
Reckless driving can include excessive speeding, weaving through traffic, unsafe passing, disregarding traffic laws, or deliberately driving in a way that creates an unreasonable risk to others.
Aggressive driving often combines several dangerous behaviors at once, leaving other motorists with little time or space to avoid a collision.
5. Running Red Lights
Drivers who enter an intersection after a traffic signal turns red can collide with vehicles, pedestrians, bicyclists, and motorcyclists who have the right of way.
Because these crashes frequently involve vehicles traveling in perpendicular directions, red-light collisions can result in serious side-impact or “T-bone” crashes.
6. Running Stop Signs and Failing to Yield
A stop sign requires drivers to come to a complete stop and proceed only when it is safe. Rolling through stop signs, failing to see approaching traffic, or misunderstanding who has the right of way can lead to intersection crashes.
Failure-to-yield accidents can also occur while making left turns, entering a roadway, merging, or encountering pedestrians in crosswalks.
7. Unsafe Lane Changes
Changing lanes safely requires checking mirrors, looking for vehicles in blind spots, signaling, and making sure adequate space is available.
A driver who moves into an occupied lane or changes lanes abruptly can cause a sideswipe collision, force another vehicle off the road, or trigger a multi-vehicle crash.
8. Improper Turns
Turning from the wrong lane, failing to signal, making an unsafe U-turn, turning across approaching traffic, or misjudging the speed of another vehicle can all cause accidents.
Left turns can be particularly challenging because a driver may need to cross one or more lanes of oncoming traffic before completing the maneuver.
9. Tailgating
Following another vehicle too closely reduces the amount of time available to respond if traffic suddenly slows or stops.
Rather than relying on the older “one car length for every 10 mph” guideline, the California DMV recommends using the three-second rule under normal conditions. Drivers should allow even more space when visibility or road conditions are poor.
10. Wrong-Way Driving
Wrong-way crashes are especially dangerous because they can result in high-speed head-on collisions.
They may occur when a driver enters a freeway using an exit ramp, turns the wrong way onto a one-way street, becomes confused by road design or signage, or is impaired.
11. Driving Under the Influence of Drugs
Illegal drugs, prescription medications, over-the-counter medications, and combinations of substances can affect a person’s ability to drive safely.
Depending on the substance, impairment may include slower reaction time, drowsiness, poor judgment, altered perception, reduced coordination, or difficulty maintaining lane position.
12. Driver Fatigue and Drowsy Driving
Driving while tired can impair attention, judgment, and reaction time. In severe cases, a driver may briefly fall asleep or experience a “microsleep” without realizing it.
Drowsy driving can be particularly dangerous during late-night and early-morning hours and on long, monotonous trips. NHTSA has identified drowsy driving as an ongoing roadway safety concern.
13. Inexperienced and Teenage Drivers
Driving safely requires experience recognizing hazards, judging distances and speeds, managing distractions, and responding appropriately to changing traffic conditions.
New drivers may be less prepared to identify dangerous situations early enough to avoid them. Distraction is also an important concern among younger drivers; the California Office of Traffic Safety reports that driver distraction is a primary cause of major-injury crashes involving teens in the state.
14. Road Rage
Road rage can escalate ordinary traffic conflicts into dangerous driving behavior.
Following another vehicle closely, deliberately cutting someone off, brake-checking, blocking another driver from changing lanes, or pursuing another vehicle can dramatically increase the risk of a crash. The safest response to an aggressive driver is generally to create distance and avoid engaging with them.
15. Street Racing
Street racing combines excessive speed with unpredictable driving behavior and roads that were never designed to function as racetracks.
Drivers may lose control, strike other motorists, or collide with pedestrians and roadside objects. Racing can also make it much more difficult to respond when another driver unexpectedly enters the roadway.
Weather, Visibility, and Road Conditions
16. Rain and Wet Roads
Rain can reduce visibility while water on the roadway reduces traction and increases stopping distance.
Federal Highway Administration data for 2019–2023 estimates that nearly 745,000 crashes per year occurred during adverse weather conditions, with rain and wet pavement accounting for a substantial share of weather-related injuries and fatalities.
Drivers should reduce their speed, increase following distance, use headlights appropriately, and avoid sudden steering or braking when roads are wet.
17. Ice
Ice can dramatically reduce tire traction, making acceleration, steering, and braking difficult.
Black ice can be especially hazardous because drivers may not recognize that the roadway is frozen until their vehicle begins to slide.
18. Snow and Slush
Snow can reduce both traction and visibility. Accumulated snow may also hide lane markings, road edges, potholes, and other hazards.
Drivers should adjust their speed and following distance for the conditions rather than assuming that traveling at the posted speed limit is always safe.
19. Fog and Poor Visibility
Fog, smoke, heavy rain, and other conditions can sharply reduce how far a driver can see.
California DMV recommends slowing down, increasing following distance, and using low-beam headlights when driving in heavy fog or smoke. High beams can reflect back through fog and make visibility worse.
20. Night Driving
Driving at night can make pedestrians, bicyclists, road hazards, curves, and other vehicles more difficult to see.
Glare from headlights, poorly lit roads, fatigue, reduced depth perception, and impaired drivers can create additional hazards after dark. Drivers should adjust their speed so they have enough time to react to anything illuminated by their headlights.
21. Dangerous Curves
Curves can become hazardous when drivers enter them too quickly, visibility is limited, the roadway is wet or icy, or signage does not adequately warn motorists of changing road conditions.
Drivers should reduce their speed before entering a sharp curve rather than braking aggressively after the vehicle is already turning.
22. Potholes and Road Defects
Potholes, uneven pavement, debris, missing signage, inadequate drainage, malfunctioning traffic signals, and poorly designed roadways may contribute to crashes.
A driver who strikes a severe pothole can damage a tire or suspension component or lose control of the vehicle while attempting to avoid the hazard.
23. Animal Crossings
Deer and other animals can enter the roadway with little warning, particularly around dawn, dusk, and nighttime hours.
Drivers traveling through areas with frequent wildlife activity should watch for warning signs, scan the edges of the roadway, and avoid swerving suddenly into another traffic lane if an animal appears.
Vehicle and Mechanical Problems
24. Tire Blowouts
A sudden loss of tire pressure can make a vehicle difficult to control, especially at highway speeds.
Worn tread, improper inflation, road hazards, overloaded vehicles, manufacturing defects, and tire damage can all contribute to tire failures. Regular inspection and proper tire maintenance can reduce some—but not all—of these risks.
25. Vehicle Defects and Mechanical Failures
Modern vehicles contain thousands of components, and failures involving brakes, steering systems, tires, airbags, electrical components, or other safety systems can sometimes contribute to crashes or make injuries more severe.
When a defective vehicle or component contributes to an accident, determining responsibility may require examining maintenance records, recall information, physical evidence, and the vehicle itself.
Can More Than One Factor Cause the Same Car Accident?
Yes. Many crashes involve several contributing factors rather than one isolated cause.
For example, a driver may be traveling too fast during heavy rain, become distracted while approaching traffic, and then be unable to stop because the road is wet. Another crash might involve an impaired driver making an unsafe turn at night.
For this reason, determining the cause of an accident often requires looking at the complete circumstances surrounding the collision.
How Is the Cause of a Car Accident Determined?
Police officers, insurance companies, accident reconstruction professionals, and attorneys may consider several forms of evidence when investigating why a collision occurred.
Evidence can include the police crash report, statements from drivers and witnesses, photographs and video, skid marks and debris, vehicle damage, traffic-camera or surveillance footage, cell phone records, vehicle event data, roadway conditions, toxicology results, and maintenance or inspection records.
No single piece of evidence necessarily tells the entire story. The goal is to reconstruct what happened before and during the collision and determine which actions or conditions contributed to it.
Injured in a Car Accident in San Diego?
Knowing what caused a car accident is often one of the first steps in determining who may be responsible.
If you were injured because another driver was speeding, distracted, impaired, reckless, or otherwise negligent, Pines Salomon Personal Injury Lawyers can investigate the circumstances surrounding your crash and explain your legal options.
Our San Diego car accident attorneys have represented injury victims for more than 30 years. Contact us for a free consultation to discuss your accident and learn what steps may be available to you.