For each crash, data were collected on up to 1,000 elements, including the condition of the truck driver and the other drivers involved before the crash; the drivers? behavior during the crash; the condition of the trucks and other vehicles; roadway factors; and weather conditions. Data were coded by crash experts, difficult cases were reviewed by FMCSA and NHTSA staff, and completed cases were put into a publicly available electronic database on FMCSA?s Web site.
National Crash Estimates
According to NHTSA?s estimate, there were approximately 120,000 fatal and injury crashes nationwide during the 33-month study period that involved at least one large truck; 141,000 large trucks were involved in those crashes. Each of the 963 LTCCS study cases was assigned a sampling weight, which allows for national estimates of total fatal and injury truck crashes during the study period.
All study results presented here are national estimates for the 141,000 large trucks that were estimated by NHTSA to have been involved in fatal and injury crashes during the study period. The estimates may differ from true values, because they are based on a probability sample of crashes and not a census of all crashes. The size of the difference may vary, depending on which LTCCS sample is the focus of a particular table or analysis.
Coding Crash Causation Variables
Many variables were coded from the hundreds of data elements collected on each crash. Three key variables were coded for assessing crash risk:
Critical Event: The action or event that put the vehicle or vehicles on a course that made the collision unavoidable. The critical event is assigned to the vehicle that took the action that made the crash inevitable.
Critical Reason: The immediate reason for the critical event (i.e., the failure leading to the critical event). The critical reason is assigned to the vehicle coded with the critical event in the crash. It can be coded as a driver error, vehicle failure, or environmental condition (roadway or weather).
Associated Factors: The person, vehicle, and environmental conditions present at the time of the crash. No judgment is made as to whether any factor is related to the reason for a particular crash, just whether the factor was present. The list of the many factors that can be coded provides enough information to describe the circumstances of the crash.
Critical Events
Three major types of critical events were assigned to large trucks:
Running out of the travel lane, either into another lane or off the road (32 percent of the large trucks in the LTCCS sample were assigned this critical event)
Vehicle loss of control due to traveling too fast for conditions, cargo shift, vehicle systems failure, poor road conditions, or other reasons (29 percent)
Colliding with the rear end of another vehicle in the truck?s travel lane (22 percent).
Critical Reasons
The percentage of large trucks coded with a critical reason depends on the type of crash:
Of the large trucks involved in all LTCCS crashes (single-vehicle and multi-vehicle), 55 percent were assigned the critical reason in crashes.
Of the large trucks involved in two-vehicle LTCCS crashes between one truck and one passenger vehicle (a car, van, pickup truck, or sport utility vehicle), 44 percent were assigned the critical reason.
Table 1 shows the critical reasons assigned, by major categories.
Table 1
Estimated Numbers of Trucks in All Crashes, by Critical Reasons
Critical Reasons Number of Trucks Percent of Total
Driver 68,000 87%
Non-Performance 9,000 12%
Recognition 22,000 28%
Decision 30,000 38%
Performance 7,000 9%
Vehicle 8,000 10%
Environment 2,000 3%
Total Number of Large Trucks Coded with Critical Reason 78,000 100%
Total Number of Large Trucks Not Coded with Critical Reason 63,000 —
Total Number of Large Trucks Involved in Crashes 141,000 —
Notes: Results shown are national estimates for the 141,000 large trucks estimated to have been involved in fatal and injury crashes during the study period. The estimates may differ from true values, because they are based on a probability sample of crashes and not a census of all crashes. Estimates are rounded to the nearest 1,000 large trucks.
Driver critical reasons are coded in four categories:
Non-Performance: The driver fell asleep, was disabled by a heart attack or seizure, or was physically impaired for another reason.
Recognition: The driver was inattentive, was distracted by something inside or outside the vehicle, or failed to observe the situation adequately for some other reason.
Decision: For example, the driver was driving too fast for conditions, misjudged the speed of other vehicles, or followed other vehicles too closely.
Performance: For example, the driver panicked, overcompensated, or exercised poor directional control.
Associated Factors
Hundreds of associated factors were collected for each vehicle in each crash. In descending order, the top 10 factors coded for large trucks and their drivers were:
Brake problems
Traffic flow interruption (congestion, previous crash)
Prescription drug use
Traveling too fast for conditions
Unfamiliarity with roadway
Roadway problems
Required to stop before crash (traffic control device, crosswalk)
Over-the-counter drug use
Inadequate surveillance
Fatigue.
Relative Risk
Relative risk analysis of the data on associated factors, using the critical event and critical reason coding, allows the sorting out of factors into those merely present at the time of the crash and those that increase the risk of having a crash. The trucks involved in LTCCS crashes can be divided into two groups: those that were assigned the critical event and critical reason and those that were not. When the presence of associated factors coded to the two groups is compared, the relative risk of each factor can be assessed, as the following examples illustrate:
If 30 percent of the trucks assigned the critical reason for a crash were coded with the driver associated factor ?traveling too fast for conditions,? while only 5 percent of the trucks that were not assigned the critical reason were coded with the same associated factor, it can be concluded that speed is a factor that increases the risk of being involved in a crash.
If 30 percent of the trucks assigned the critical reason for a crash were coded with the driver associated factor ?prescription drug use,? while 30 percent of the trucks that were not assigned the critical reason were also coded with the same associated factor, it can be concluded that prescription drug use is not a factor that increases the risk of being involved in a crash.
Table 2 shows the 19 associated factors that were coded most frequently for large trucks in the LTCCS, where there was a statistically significant association between the factor and the assignment of the critical reason. The order of the factors in the table is based on the number and percentage of trucks assessed with each factor. The relative risk number is a ratio of the critical reason coding for trucks coded with the factor, compared with trucks not coded with the factor. Thus, Table 2 shows that a truck with brake problems was 170 percent more likely to be coded with the critical reason for a crash than a truck that was not coded with the brake problems associated factor.
Table 2
Associated Factors Assigned in Large Truck Crashes and Their Relative Risk Importance
Factors Number of Trucks Percent of Total Relative Risk
Vehicle: Brake problems 41,000 29% 2.7
Driver: Traveling too fast for conditions 32,000 23% 7.7
Driver: Unfamiliar with roadway 31,000 22% 2.0
Environment: Roadway problems 29,000 20% 1.5
Driver: Over-the-counter drug use 25,000 17% 1.3
Driver: Inadequate surveillance 20,000 14% 9.3
Driver: Fatigue 18,000 13% 8.0
Driver: Felt under work pressure from carrier 16,000 10% 4.7
Driver: Made illegal maneuver 13,000 9% 26.4
Driver: Inattention 12,000 9% 17.1
Driver: External distraction 11,000 8% 5.1
Vehicle: Tire problems 8,000 6% 2.5
Driver: Following too close 7,000 5% 22.6
Driver: Jackknife 7,000 5% 4.7
Vehicle: Cargo shift 6,000 4% 56.3
Driver: Illness 4,000 3% 34.0
Driver: Internal distraction 3,000 2% 5.8
Driver: Illegal drugs 3,000 2% 1.8
Driver: Alcohol 1,000 1% 5.3
Notes: Results shown are national estimates for the 141,000 large trucks estimated to have been involved in fatal and injury crashes during the study period. The estimates may differ from true values, because they are based on a probability sample of crashes and not a census of all crashes. Estimates are rounded to the nearest 1,000 large trucks.
Of the top 10 associated factors coded for large trucks, 3 do not appear in Table 2. For those three associated factors—traffic flow interruption, prescription drug use, and required to stop before crash—there was no significant difference in the frequency at which trucks with and without the factors were coded with the critical reason for a crash.
It is important to note both the number of times an associated factor is coded and its relative risk ratio. For example, the brake problems associated factor is the most frequently coded (29 percent), but it has a lower relative risk ratio than those for 13 other factors. Pre-crash cargo shift, with the highest relative risk ratio (56.3), was reported for only 4 percent of the large trucks involved in LTCCS crashes.
Of the 19 factors listed in Table 2, 15 are driver factors. Those 15 driver factors can be divided into two major groups. One group—fatigue, illness, and drug use (both legal and illegal)—reflects the condition of the driver before the crash. The other group—excessive speed, inadequate surveillance, illegal maneuver, inattention, distraction (outside the truck and inside the truck), and following too close—reflects driving mistakes.
Large Truck – Passenger Vehicle Crashes
One-half of the LTCCS crashes involved collisions between a large truck and a passenger vehicle (car, pickup truck, van, or sport utility vehicle). In those crashes, the same associated factors coded most often for the large trucks usually were also coded most often for the passenger vehicles. For both large trucks and passenger vehicles, there was a statistically significant link between the following 10 associated factors (listed in descending order according to how often they were coded for the large truck) and coding of the critical reason:
1.Interruption of the traffic flow
2.Unfamiliarity with roadway
3.Inadequate surveillance
4.Driving too fast for conditions
5.Illegal maneuver
6.Inattention
7.Fatigue
8.Illness
9.False assumption of other road user's actions
10.Distraction by object or person inside the vehicle.
There are some important differences in the coding of associated factors between the two vehicle types. For large trucks, but not passenger vehicles, following too closely (a traffic situation that required a stop before the crash) and distraction outside the vehicle were statistically related to assignment of the critical reason. In addition, vehicle factors that were not coded or examined for the passenger vehicles (brakes, tires, jackknife, and cargo shift) were statistically linked to assignment of the critical reason for large trucks.
For passenger vehicles, but not for trucks, alcohol and illegal drug use have a statistically significant association with coding of the critical reason. These factors, combined with fatigue (coded twice as often for passenger vehicles as for large trucks) and illness (coded five times more often for passenger vehicles), show that passenger vehicle drivers were subject to adverse physical conditions more often than truck drivers were before the crashes occurred.
Have You Been Injured In A South Carolina Area Truck Accident?
If you or a loved one was injured in a commercial truck accident in South Carolina, you should speak with a truck accident lawyer as soon as possible. Contact us online or call our Charleston, South Carolina office directly at 843.488.2359 to schedule your consultation. We are also able to meet clients at our Conway, Myrtle Beach, Murrells Inlet, Mt. Pleasant, North Myrtle Beach or North Charleston office locations.
