Another important feature of NMVCCS is the assessment of the critical reason underlying the critical
event. The critical reason is determined by a thorough evaluation of all the potential problems related
to errors attributable to the driver, the condition of the vehicle, failure of vehicle systems, adverse
environmental conditions, and roadway design. Some of the highlights of the critical reason
underlying the critical event are presented below.
In cases where the researchers attributed the critical reason to the driver, about 41 percent of the
critical reasons were recognition errors (inattention, internal and external distractions, inadequate
surveillance, etc.). In addition, about 34 percent of the critical reasons attributed to the driver were
decision errors (driving aggressively, driving too fast, etc.) and 10 percent were performance errors
(overcompensation, improper directional control, etc.). The researchers also made an assessment of
other factors associated with the crash, such as interior non-driving activities. In fact, about 18
percent of the drivers were engaged in at least one interior non-driving activity. The most frequent
interior non-driving activity was conversation, either with other passengers in the vehicle or on a cell
phone, especially among young (age 16 to 25) drivers. Among other associated factors, fatigued
drivers were twice as likely to make performance errors as compared to drivers who were not
fatigued. The information about driver-related critical reasons will assist in the development of crash
avoidance systems and collision warning systems, as well as improve the design of dashboard
electronics, or telematics, that reduce the potential for driver inattention. The effectiveness of vehicle-based
countermeasures in mitigating the effects of various driver performance, recognition, and
decision errors could be evaluated using this information.