Evaluation of Iowa crash data reported to MCMIS Crash File

Abstract

This report is part of a series of reports evaluating the data reported to the Motor Carrier Management Information System (MCMIS) Crash File undertaken by the Center for National Truck and Bus Statistics at the University of Michigan Transportation Research Institute. The earlier studies showed that reporting to the MCMIS Crash File was incomplete. This report examines the factors that are associated with reporting rates for the state of Iowa. MCMIS Crash File records were matched to the Iowa Police Accident Report (PAR) file to determine the nature and extent of underreporting. Overall, it appears that Iowa is reporting 71.6 percent of crash involvements that should be reported to the Crash file. Reporting rates vary by crash severity and vehicle type. Overall, about 94.1 percent of fatal involvements are reported, compared with 86.4 percent of injury, transported involvements, and 61.4 percent of towed, disabled involvements. Crashes involving large trucks such as tractor-semitrailers or doubles combinations were more likely to be reported than crashes involving single-unit trucks or buses. Crashes covered by the Iowa State Patrol were more likely to be reported than those covered by either county sheriffs or local police departments. Missing data rates are low for most variables, although rates are elevated for body type, driver condition, roadway access, and roadway surface condition. Hazardous materials variables are also problematic. Inconsistencies for non-missing values between the two files may be explained by corrections applied in one file but not the other.