Figure 2-1: A step-by-step description of the implementation procedure follows. The step numbers (shown in parentheses) correspond to the numbers in parentheses in the diagram.
(1) Identify carriers with one or more compliance reviews (CRs) in 2002 that were still active 12 months after their CRs.
There were 9,172 carriers that received CRs in 2002, were still active 12 months after their CRs (i.e., throughout their post-CR periods), and met the following conditions:
- The carrier had to be either interstate or intrastate HM (hazardous materials).
- The carrier must have had 1 or more power units during the pre-CR and post-CR periods (i.e., 12 months before and after the CR).
- If the carrier had more than one CR in 2002, the latest one was used.
- The carrier’s crash and power unit data had to pass edit checks designed to screen out erroneous data.
(2) Calculate the pre-CR average crash rate.
The 9,172 carriers that received CRs in 2002 and were still active 12 months after their CRs had a pre-CR average crash rate of 4.032 crashes per 100 power units. This average was obtained by dividing the total number of carriers’ state-reported crashes in the 12 months before their 2002 CRs by the total number of carriers’ power units and then multiplying by 100. The power unit data came from the MCMIS Census File. The data were obtained from compliance reviews and updated Form MCS-150 information submitted by carriers. In the rate calculation for each carrier, the power unit data were taken from the SafeStat run for the month following the carrier’s CR. That way, the power unit data used in the rate calculation would reflect the power unit data collected during the CR.
(3) Calculate the post-CR average crash rate.
The 9,172 carriers that received CRs in 2002 and were still active 12 months after their CRs had a post-CR average crash rate of 3.712 crashes per 100 power units. This average was obtained by dividing the total number of carriers’ state-reported crashes in the 12 months after their 2002 CRs by the total number of carriers’ power units and then multiplying by 100. The power unit data came from the MCMIS Census File. In the rate calculation for each carrier, the power unit data were taken from the SafeStat run one year after the run used to calculate the carrier’s pre-CR crash rate.
For example, if a carrier had a CR on January 21, 2002, then power unit data from the February 2002 SafeStat run would have been used to calculate its pre-CR crash rate, and power unit data from the February 2003 SafeStat run would have been used to calculate its post-CR crash rate. The carrier’s pre-CR period (i.e., the 12 months prior to the CR) would have been January 21, 2001 to January 20, 2002, while its post-CR period (i.e., the 12 months after the CR) would have been January 22, 2002 to January 21, 2003. This information is shown in the timeline in Figure 2-2.
(4) Calculate the reduction in the average crash rate.
(4a) Calculate the reduction using the data for the carriers with CRs in 2002.
The percentage change in the average crash rate of carriers with CRs in 2002 was calculated as follows:
Percentage Change in Average Crash Rate of Carriers with CRs in 2002
Post-CR Average Crash Rate – Pre-CR Average Crash Rate
= —————————————————————————— X 100
Pre-CR Average Crash Rate
3.712 – 4.032
= ——————— X 100
4.032
= –7.94% (i.e., a decrease of 7.94 percent)
(4b) Adjust the reduction for underlying factors in the general carrier population.
The change in the average crash rate of the carriers that received CRs (i.e., the CR group) was not adjusted for underlying factors occurring in the general carrier population. For example, if the average crash rate of all carriers had decreased during the same period in which the CR group’s average crash rate decreased, then the reduction in the CR group’s average crash rate calculated in Step 4a would have been exaggerated. That is, not all of the reduction would have been the result of the CRs. Conversely, if the average crash rate of the general carrier population had increased during this period, then the reduction in the CR group’s average crash rate calculated in Step 4a would have been less than the actual crash rate reduction due to the CRs.
Another factor that must be considered in the analysis of carriers that received CRs in 2002 is improved crash reporting. Over the past several years, the FMCSA has made a concerted effort to improve the timeliness and completeness of crash reporting by the states. As a result, crashes are being reported earlier and more completely. This improved crash reporting will tend to increase the post-CR average crash rate and produce a smaller crash rate reduction in the CR group’s average crash rate than actually occurred.
To eliminate the effects of outside factors, a control group of carriers was selected. This control group consisted of all carriers that did not receive CRs in 2002. Any change in the average crash rate of the control group must have been due to factors affecting the entire carrier population, e.g., improved crash reporting. Thus, the change in the average crash rate of the control group was calculated and then subtracted from the change in the average crash rate of the carriers that received CRs in 2002. The difference resulting from this calculation represents the change in the average crash rate of the carriers that received CRs in 2002 that was solely the result of the CRs.
To be eligible for the control group, a carrier had to meet the following conditions:
- The carrier had to be either interstate or intrastate HM.
- The carrier must have had 1 or more power units during the pre-CR and post-CR periods (i.e., January 2001 to December 2003).
- The carrier must have been active throughout the pre-CR period (i.e., January 2001 to December 2002) and the post-CR period (i.e., January 2002 to December 2003).
- The carrier’s crash and power unit data had to pass the same edit checks used on the crash and power unit data of the carriers with CRs in 2002.
There were 396,478 carriers that met these criteria.
The change in the average crash rate of the control (i.e., non-CR) group was calculated as follows:
Percent Change Post-CR Average Crash Rate – Pre-CR Average Crash Rate
in Average = ————————————————————————— X 100
Crash Rate Pre-CR Average Crash Rate
The pre-CR crash rate is the average crash rate for the entire pre-CR period, i.e., 2001-2002, while the post-CR crash rate is the average crash rate for the entire post-CR period, i.e., 2002-2003. The pre-CR and post-CR average crash rates were calculated as follows: [4]
Pre-CR Crashes in 2001 + Crashes in 2002
Average = ———————————————————————————
Crash Rate Power Units at the end of 2001 + Power Units at the end of 2002
Post-CR Crashes in 2002 + Crashes in 2003
Average = ———————————————————————————
Crash Rate Power Units at the end of 2002 + Power Units at the end of 2003
The 396,478 carriers in the control group had a pre-CR average crash rate of 1.656 crashes per 100 power units and a post-CR average crash rate of 1.733 crashes per 100 power units.
The percentage change in the average crash rate of the control group was calculated as follows:
Percentage Change in Average Crash Rate of Control Group
Post-CR Average Crash Rate – Pre-CR Average Crash Rate
= ——————————————————————————— X 100
Pre-CR Average Crash Rate
= ———————— X 100
1.656
= +4.65% (i.e., an increase of 4.65 percent)
This increase in the average crash rate of the control group (and therefore, the general carrier population) is the sum of the effects of the improved crash reporting and any change in the average crash rate of the general carrier population. To determine how much of the increase was due to each factor, a separate series of calculations was performed. The calculations showed that there was a 2.90 percent increase in the average crash rate of the general carrier population. Therefore, the 4.65 percent increase in the average crash rate of the control group (and therefore, the general carrier population) was the sum of a 2.90 percent increase due to an increase in the crash rate of the general carrier population and a 1.75 increase due to improved crash reporting. These calculations are shown in Appendix B.
Therefore, the adjusted change in the average crash rate due to the CRs conducted in 2002 was:
Adjusted Change in Crash Rate due to CRs Conducted in 2002
= Percentage Change in Average Crash Rate of Carriers with CRs in 2002
–
Percentage Change in Average Crash Rate of Control Group due to Increased Crash
Reporting
= (–7.94) – (4.65)
= –12.6% (i.e., a decrease of 12.6 percent)
(5) Calculate the number of post-CR power units, i.e., the number of power units 12 months after the CRs in 2002.
The 9,172 carriers that received CRs in 2002 and were still active 12 months after their CRs had a total of 280,685 power units 12 months after their CRs. This number was used to calculate the post-CR average crash rate in Step 3.
(6) Estimate the number of crashes avoided in 2002-2003 as a result of the CRs conducted in 2002.
The estimated number of crashes avoided in 2002-2003 by the 9,172 carriers that received CRs in 2002 and were still active 12 months after their CRs was calculated as follows:
Crashes Avoided in 2002-2003 by Carriers with CRs in 2002
= Pre-CR Average Crash Rate X Crash Rate Reduction (%) X Post-CR Power Units
= 4.032 crashes per 100 power units X 12.6% X 280,685 power units
= 1,426 crashes
Next, estimates were made of the number of crashes avoided in 2002-2003 by the carriers receiving CRs in 2002 by severity, i.e., fatal, injury, and towaway. [5] State-reported crash data in the MCMIS were used to compute these proportions. For crashes involving large trucks or motorcoaches (i.e., cross-country or intercity buses) in 2002-2003, the period in which the benefits of the CRs conducted in 2002 would occur, 3.7 percent were fatal crashes, 47.5 percent were injury crashes, and 48.8 percent were in towaway crashes.
Applying these proportions to the estimate of 1,426 crashes avoided produced the following results:
Fatal crashes = 1,426 X 3.7% = 53
Injury crashes = 1,426 X 47.5% = 677
Towaway crashes = 1,426 X 48.8% = 696
(7) Calculate the average numbers of fatalities and injuries per crash in 2002-2003.
The average number of fatalities per fatal crash was calculated from data from the Fatality Analysis Reporting System (FARS), which is maintained by the National Highway Traffic Safety Administration (NHTSA). The period in which the benefits of the CRs conducted in 2002 occurred is 2002-2003. For crashes in 2002-2003 involving large trucks or motorcoaches (i.e., cross-country or intercity buses), the ratio was 1.17 fatalities per fatal crash.
The number of injuries per crash involves fatal as well as injury crashes, since fatal crashes can also result in injuries. State-reported crash data from the MCMIS Crash File were used to compute the average numbers of injuries in fatal and injury crashes. For 2002-2003 large truck and motorcoach crashes, the averages were as follows:
- Fatal crashes: 1.09 injuries per crash
- Injury crashes: 1.52 injuries per crash
(8) Calculate the benefits (i.e., lives saved and injuries avoided) that occurred in 2002-2003.
The estimated number of lives saved in the crashes avoided in 2002-2003 by the carriers with CRs in 2002 was calculated as follows:
Number of lives saved in fatal crashes avoided in 2002-2003 by carriers with CRs in
2002
= Number of fatal crashes avoided X Average number of fatalities per fatal crash
= 53 X 1.17
= 62 lives saved
The estimated number of injuries avoided in the crashes avoided in 2002-2003 by the carriers with CRs in 2002 was calculated as follows:
Number of injuries avoided in crashes avoided in 2002-2003 by carriers with CRs in
2002
= Number of fatal crashes avoided X Average number of injuries per fatal crash
+
Number of injury crashes avoided X Average number of injuries per injury crash
= 53 X 1.09 + 677 X 1.52
= 1,087 injuries avoided
Figure 2-2:
For example, if a carrier had a CR on January 21, 2002, then power unit data from the February 2002 SafeStat run would have been used to calculate its pre-CR crash rate, and power unit data from the February 2003 SafeStat run would have been used to calculate its post-CR crash rate. The carrier’s pre-CR period (i.e., the 12 months prior to the CR) would have been January 21, 2001 to January 20, 2002, while its post-CR period (i.e., the 12 months after the CR) would have been January 22, 2002 to January 21, 2003. This information is shown in the timeline in Figure 2-2.