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The Most Common Cause of Car Accidents

The McClellan Law Firm

For two and a half years, the National Highway Traffic Safety Administration commissioned an in-depth look at the causes of car crashes. It was entitled the National Motor Vehicle Crash Causation Survey, and it included an intensive investigation of 5,470 car crashes from 2005 to 2007. This sample was chosen to represent an annual crash rate of more than 2 million, involving 6 million drivers and passengers.

The investigation gathered an incredible amount of data that divided collisions into four stages:

  • Pre-crash movement
  • Pre-crash event
  • Critical reason
  • Associated factors

According to the study, these four moments are often what constitute any collision or near-collision. Pre-crash movement is what the inciting vehicle was doing just prior to the crash. This would include making a turn, stopping at a light, switching lanes, etc. The pre-crash event is what leads the vehicles to be on a collision course that is unavoidable, assuming normal or reasonable driving skill.

“Critical Reasons” & What They Signify

The most important part of the crash is what we are primarily discussing today: the critical reason. The critical reasons is the cause of the pre-crash event, what ultimately leads to the collision. As the last failure in the causal chain, it is the turning point in any crash. The critical reason can be assigned to the environment, the vehicle, or the driver—anything that directly led to a fundamentally unavoidable collision.

The study discovered the following about the critical reasons for crashes:

  • 94 percent of critical reasons were assigned to drivers
  • 2 percent of critical reasons were assigned to vehicles
  • 2 percent were assigned to environmental causes
  • The final 2 percent of critical reasons were unknown

It’s important to note that critical reason assignment is not about assigning blame, but about recognizing where the root cause of the crash was found. For example, a driver might be the critical reason for a crash, but it does not necessarily make them at-fault—for example, a percentage of driver errors include having a heart attack while at the wheel. It simply means that their decision or circumstances immediately led to the pre-crash event. This distinction matters when investigating preventable conditions and negligence claims.

If you are unsure about the causes of your car crash, speak to our attorneys for legal clarification.

Critical Reasons Assigned to Drivers

As driver errors are the overwhelming cause behind most car crashes, we will focus our attention on them. Driver errors are broadly defined—they include everything from distractions within the car, poor assumption of other drivers’ behavior, panicking in a pre-crash movement, or even falling asleep at the wheel.

Driver errors are divided into four sub-categories:

  • Recognition errors (40%)
  • Decision errors (34%)
  • Performance errors (10%)
  • Non-Performance Errors (7%)
  • Unknown causes (8%)

Recognition errors have to do with the driver not seeing or registering the elements that led to the crash. This includes not paying attention, daydreaming, and things of that nature. In this category, the most common critical reason was “inadequate surveillance”—which means the single highest cause for car crashes was drivers not checking their surroundings well enough. According to the statistics, inadequate surveillance accounts for over 400,000 crashes a year—nearly a fifth of all crashes annually.

Other leading driver errors included internal distraction (this includes using the phone will driving), driving too fast for conditions, or overcompensating in an avoidance maneuver. Interestingly, illegal maneuvers only accounted for less than 4% of driver-caused crashes. This means that much of what led to collisions in this survey were perfectly legal circumstances, despite the negligence of drivers or other parties.

Vehicle Failures & Malfunctions

While only accounting for a small percentage of critical reasons, do not misunderstand these statistics—vehicle failures are still an associated factor in many collisions. They are just not necessarily what led directly to the pre-crash event (we can’t stress that distinction enough).

The top two critical reasons for collisions caused by vehicle failure are:

Tire failure accounted for 40 percent of vehicle malfunctions that led to crashes. This includes tire blowouts and other issues associated with inflation. “Degradation” was also a factor, as functional tires will still have a rate of failure without proper care. Brake failure accounted for an additional 25 percent of collisions.

Environmental Factors

For nearly 50 percent of all critical reasons attributed to environmental factors, the cause was slick roads (either from ice or debris). In fact, while you might think environmental factors would primarily be about the weather, the state of the roadway was 75 percent more likely to cause a collision. In fact, fog, rain, and snow caused less than 5 percent of collisions, with only another 4 percent attributed to other weather conditions. Ultimately, that may indicate that the overwhelming majority of car collisions are preventable.


The NHTSA’s investigation into car collisions revealed truly important findings. The vast majority of crashes are caused by driver errors, followed by poor vehicle maintenance or repairs. The vast majority of accidents overall, in fact, is caused by inattention or poor observation. As personal injury attorneys, knowing that collisions are caused by preventable conditions makes our role even more crucial to car accident victims.

If you have been harmed in a car crash, let our personal injury attorneys investigate the cause of your accident. Statistically speaking, someone’s error caused your accident—whether it was another driver’s error or a manufacturer defect. Speak with The McClellan Law Firm today.