Published by NHTSA’s National Center for Statistics and Analysis 1200 New Jersey Avenue SE., Washington, DC 20590

TRAFFIC SAFETY FACTS

Crash • Stats

DOT HS 812 115 A Brief Statistical Summary February 2015

Critical Reasons for Crashes Investigated in the 

National Motor Vehicle Crash Causation Survey

Summary

The National Motor Vehicle Crash Causation Survey (NMVCCS), 

conducted from 2005 to 2007, was aimed at collecting on-scene 

information about the events and associated factors leading up 

to crashes involving light vehicles. Several facets of crash occurrence were investigated during data collection, namely the precrash movement, critical pre-crash event, critical reason, and the 

associated factors. A weighted sample of 5,470 crashes was investigated over a period of two and a half years, which represents an 

estimated 2,189,000 crashes nationwide. About 4,031,000 vehicles, 

3,945,000 drivers, and 1,982,000 passengers were estimated to have 

been involved in these crashes. The critical reason, which is the 

last event in the crash causal chain, was assigned to the driver in 

94 percent (±2.2%)†

 of the crashes. In about 2 percent (±0.7%) of the 

crashes, the critical reason was assigned to a vehicle component’s 

failure or degradation, and in 2 percent (±1.3%) of crashes, it was 

attributed to the environment (slick roads, weather, etc.). Among 

an estimated 2,046,000 drivers who were assigned critical reasons, 

recognition errors accounted for about 41 percent (±2.1%), decision errors 33 percent (±3.7%), and performance errors 11 percent 

(±2.7%) of the crashes.

Introduction

Databases such as the National Automotive Sampling System 

(NASS) Crashworthiness Data System (CDS) do not provide information on pre-crash scenarios and the reason underlying the critical pre-crash events. In 2005, the National Highway Traffic Safety 

Administration (NHTSA) was authorized under Section 2003(c) 

of the Safe, Accountable, Flexible, Efficient, Transportation Equity 

Act: A Legacy for Users (SAFETEA-LU) to conduct a national survey to collect on-scene data pertaining to events and associated 

factors that possibly contributed to crash occurrence. NHTSA’s 

National Center for Statistics and Analysis (NCSA) conducted 

NMVCCS from July 3, 2005, to December 31, 2007. Crashes were 

investigated at the crash scene to collect driver, vehicle, and environment-related information pertaining to crash occurrence, with 

a focus on driver’s role. The targeted information was captured 

mainly through four data elements: (i) movement prior to critical pre-crash event (i.e., the movement of the vehicle immediately 

before the occurrence of the critical event); (ii) critical pre-crash 

event (i.e., the circumstance that led to vehicle’s first impact); (iii) 

critical reason for the critical pre-crash event (i.e., the immediate 

reason for the critical event, which is often the last failure in the 

causal chain of events leading up to the crash); and (iv) the crashassociated factors (i.e., the factors that are likely to add to the probability of crash occurrence). This was done with reference to the 

crash envelope that comprises of a sequence of events, referring to 

the above data elements, which eventually led to the crash.

This Crash•Stats presents some statistics related to one of the 

four data elements, namely “critical reason for the critical precrash event.” The data obtained through the sample of 5,470 

NMVCCS crashes and the weights associated with them were 

used to obtain national estimates of frequencies and percentages 

along with their 95-percent confidence limits, as presented in the 

following sections.

Critical Reasons for the Critical Pre‐Crash Event

The critical reason is the immediate reason for the critical pre-crash event 

and is often the last failure in the causal chain of events leading up to the 

crash. Although the critical reason is an important part of the description 

of events leading up to the crash, it is not intended to be interpreted as the 

cause of the crash nor as the assignment of the fault to the driver, vehicle, 

or environment.

A critical reason can be assigned to a driver, vehicle, or environment. Normally, one critical reason was assigned per crash, based 

upon NMVCCS researcher’s crash assessment. The critical reason 

was assigned to the driver in an estimated 94 percent (±2.2%) of 

the crashes (Table 1). In addition, the critical reason was assigned 

to the vehicle in an estimated 2 percent (±0.7%) and to the environment in about 2 percent (±1.3%) of the crashes.

Table 1. Driver-, Vehicle-, and Environment-Related 

Critical Reasons

Critical Reason 

Attributed to

Estimated

Number

Percentage*

± 95% conf. limits

Drivers 2,046,000 94% ±2.2%

Vehicles 44,000 2% ±0.7%

Environment 52,000 2% ±1.3%

Unknown Critical Reasons 47,000 2% ±1.4%

Total 2,189,000 100%

*Percentages are based on unrounded estimated frequencies

(Data Source: NMVCCS 2005–2007)

The critical reasons related statistics are presented in detail 

in Table 2 for drivers, Table 3 for vehicles, and Table 4 for 

environment.

Critical reason attributed to drivers

The critical reason was assigned to drivers in an estimated 2,046,000 

crashes that comprise 94 percent of the NMVCCS crashes at the 

national level. However, in none of these cases was the assignment 

intended to blame the driver for causing the crash. The driver- † 95% conf. limits: ± tα/2; deg. freedom × Std. Dev. (α = 0.05, t-value = 2.179)
Published by NHTSA’s National Center for Statistics and Analysis 1200 New Jersey Avenue SE., Washington, DC 20590

2

11222-022315-v3

related critical reasons are broadly classified into recognition 

errors, decision errors, performance errors, and non-performance 

errors. Statistics in Table 2 show that the recognition error, which 

included driver’s inattention, internal and external distractions, 

and inadequate surveillance, was the most (41% ±2.2%) frequently 

assigned critical reason. Decision error such as driving too fast 

for conditions, too fast for the curve, false assumption of others’ 

actions, illegal maneuver and misjudgment of gap or others’ speed 

accounted for about 33 percent (±3.7%) of the crashes. In about 11 

percent (±2.7%) of the crashes, the critical reason was performance 

error such as overcompensation, poor directional control, etc. 

Sleep was the most common critical reason among non-performance errors that accounted for 7 percent (±1.0%) of the crashes. 

Other driver errors were recorded as critical reasons for about 8 

percent (±1.9%) of the drivers.

Table 2. Driver-Related Critical Reasons

Critical Reason

Estimated (Based on 94% of the 

NMVCCS crashes)

Number

Percentage*

± 95% conf. limits

Recognition Error 845,000 41% ±2.2%

Decision Error 684,000 33% ±3.7%

Performance Error 210,000 11% ±2.7%

Non-Performance Error (sleep, etc.) 145,000 7% ±1.0%

Other 162,000 8% ±1.9%

Total 2,046,000 100%

*Percentages are based on unrounded estimated frequencies

(Data Source: NMVCCS 2005–2007)

Critical reason attributed to vehicles

The critical reason was assigned to vehicles in an estimated 

44,000 crashes comprising about 2 percent of the NMVCCS 

crashes, though none of these reasons implied a vehicle causing the crash. There were no detailed inspections of vehicles 

during the NMVCCS on-scene crash investigation; the vehiclerelated critical reasons were mainly inferred through external 

visual inspection of the vehicle components. This resulted in 

only mostly external, easily visible factors (tires, brakes, steering 

column, etc.) that were cited as the few vehicle-related critical 

reasons. The related statistics may not, therefore, be representative of the role of other internal vehicle related problems that 

might have led to the crash. Of the small percentage (2%) of the 

crashes in which the critical reason was assigned to the vehicle, 

the tire problem accounted for about 35 percent (±11.4%) of the 

crashes. Brake related problems as critical reasons accounted for 

about 22 percent (±15.4%) of such crashes. Steering/suspension/

transmission/engine-related problems were assigned as critical reasons in 3 percent (±3.3%) of such crashes. Other vehiclerelated problems coded as critical reasons were assigned in 

about 40 percent (±24.0%) percent of such crashes.

Table 3. Vehicle Related Critical Reasons

Critical Reason 

Estimated (Based on 2% of 

the NMVCCS crashes)

Number

Percentage*

± 95% conf. limits

Tires /wheels-related 15,000 35% ± 11.4%

Brakes-related 10,000 22% ± 15.4%

Steering/suspension/transmission/

engine-related 2,000 3% ± 3.3%

Other/unknown vehicle-related problems 17,000 40% ± 24.0%

Total 44,000 100%

*Percentages are based on unrounded estimated frequencies

(Data Source: NMVCCS 2005–2007)

Critical reason attributed to environment

The critical reason was assigned to about 2 percent of the estimated 2,189,000 NMVCCS crashes. However, none of these is 

suggestive of the cause of the crash. Table 4 presents statistics 

related to crashes in which the critical reason was attributed 

to roadway and atmospheric conditions. In about 50 percent 

(±14.5%) of the 52,000 crashes the critical reason was attributed 

to slick roads. Glare as a critical reason accounted for about 17 

percent (±16.7%) of the environment-related crashes, and view 

obstruction was assigned in 11 percent (±7.2%) of the crashes. 

Signs and signals accounted for 3 percent (±2.5%) of such 

crashes. In addition, in 52,000 of the crashes with a critical reason attributed to the environment, the weather condition (fog/

rain/snow) was cited in 4 percent (±2.9%) of the crashes.

Table 4. Environment-Related Critical Reasons

Critical Reason 

Estimated (Based on 2% of the 

NMVCCS crashes)

Number

Percentage*

± 95% conf. limits

Slick roads (ice, loose debris, etc.) 26,000 50% ±14.5%

Glare 9,000 17% ±16.7%

View obstructions 6,000 11% ±7.2%

Other highway-related condition 5,000 9% (0, 9.9)††%

Fog/rain/snow 2,000 4% ±2.9%

Other weather-related condition 2,000 4% (0.0, 9.1)††%

Signs/signals 1,000 3% ± 2.5%

Road design 1,000 1% (0, 3.3)††%

Total 52,000 100%

*Percentages are based on unrounded estimated frequencies

††Conf. limits with lower limit 0

(Data Source: NMVCCS 2005–2007)

Suggested APA Format Citation for This Document:

Singh, S. (2015, February). Critical reasons for crashes investigated in 

the National Motor Vehicle Crash Causation Survey. (Traffic Safety 

Facts Crash•Stats. Report No. DOT HS 812 115). Washington, DC: 

National Highway Traffic Safety Administration.

This Crash•Stats was prepared by Santokh Singh, senior mathematical statistician, Bowhead Systems Management, Inc., working under contract with the Mathematical Analysis Division 

of the National Center for Statistics and Analysis, NHTSA. For 

questions regarding the information presented in this document, please contact NCSAWEB@dot.gov.