Connecticut had one of the highest rates in the nation of motor vehicle fatalities in which drivers were alcohol impaired in 2013, the most recent year for which data is available – 41 percent, compared to the national average of 31 percent, according to federal estimates. But the state also had one of the lowest rates nationally of reporting drunk-driving data in fatal accidents – a lapse that hampers efforts to gauge the impaired-driving problem and to develop and evaluate programs to address it, experts say. Connecticut reported blood-alcohol concentration (BAC) results for just 45 percent of fatally injured drivers — far lower than the national average of 71 percent, according to data collected by the National Highway Traffic Safety Administration (NHTSA). Only Mississippi reported a lower rate of such testing. Thirty-four states reported testing rates of more than 70 percent.