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Examination of DWI Conviction Rate Procedures:

Ralph K. Jones
Connie H. Wiliszowski
John H. Lacey

August 1999

Prepared for:

U.S. Department of Transportation
National Highway Traffic Safety Administration
Washington, D.C. 20590

Contract Number DTNH22-97-D-35018

Mid-America Research Institute, Inc. of New England Winchester, Massachusetts

This report summarizes how DWI conviction rates are calculated. Arrest and conviction data were obtained from ten sites along with information and opinions from local officials on how DWI conviction rates should be calculated. When rates or calculation methods were released, calculation methods differed among the sites, and the type of conviction rate quoted was largely a function of the type of agency doing the quoting and the data available to that agency. The DWI conviction process can be effected by plea bargains, speedy trial laws, offenders who fail to appear, and pre-trial diversion practices. Although it would seem that a state-wide, complex system would be necessary to provide all the data required to provide a system-wide conviction rate, the smallest site included in the study proved that, with cooperation from all the organizations involved, an effective system can be set up in any jurisdiction. The objective of the project was to examine various conviction rate formulas, but was not concerned with the success or lack thereof of convicting persons charged with DWI offenses in the participating jurisdictions. Individuals in those sites who agreed to participate in the project should be commended for providing data for the study, general system information, and views on the subject.



Travis County, Texas is located in east, central Texas and includes the state capital of Austin. The U.S. Census Bureau reports a population in 1996 of 664,800, up from a population in 1990 of 576,400. The 1990 population was classified as 91% urban and 9% rural. The 1996 per capita income for the county was $21,127. The state capital, Austin, is located in Travis County, Texas.

DWI Enforcement System

Project staff visited Austin, Texas and met with staff at various agencies relative to the project: the Texas Department of Transportation (TXDOT), the Department of Public Safety (DPS) Traffic Law Enforcement Division, the Driver Information Center (DIC), the Austin Police Department (APD), Travis County Sheriff=s Department, the Travis County Prosecutor=s Office, and the Texas Alcohol and Beverage Commission (TABC). All of the contacts proved helpful in sharing information and appeared interested in the project.

The Department of Public Safety (DPS) is the Texas state police agency. The Department enforces traffic laws on Texas highways (federal, state, and county) through the Traffic Law Enforcement (TLE) Division. The Division includes specific services, the largest of which is the Highway Patrol. The TLE tracks DWI arrests, but not convictions. This holds true for the other enforcement agencies we talked with (APD, the Sheriff=s Department, and TABC). None of these enforcement agencies were aware of DWI case disposition rates.

Prosecution Patterns and Beliefs

There is a two-tier court system for handling DWI offenders. The courts which handle first-time offenders (unless, for example, there is a felony charge for a fatality) are the County Courts and the County Court of Law Courts. Multiple offenders and/or felony cases are handled in District Courts.

The Travis County Prosecutors Office has an information department which records case dispositions, but the Trial Chief was not comfortable with the accuracy of that information. He believed the DWI conviction rate would be in the 80% range if it were to be calculated.

It does not appear that the agencies we met with have tracked DWI conviction rates in the past.

Quoted Conviction Rates

Texas Department Of Transportation. TXDOT and DPS are two of the principal agencies in Texas which collect and track data pertinent to this project. TXDOT receives arrest data from DPS and the Office of Court Administration (OCA). TXDOT reported that the conviction rate for Texas for 9/1/95 through 9/31/96 could be quickly calculated at 63% for County Court based on the annual report for the fiscal year 1996 published by the Texas Judicial Council (Table 2-6). District Court activity reflected a 65% conviction rate. The formula used was:

   Conviction Rate = RC = Number of guilty dispositions / Number of all dispositions

As stated by persons at other project sites, there could be a public relations backlash if there are misinterpretations of what the rate represents.

Table 2-6: Quoted Convictions Rates, Rc, FY 1996, for Travis County, Texas

Felony DWI
Convictions 7,424 66,051
Dispositions 11,475 104,241
Conviction Rate 64.7% 63.4%

Texas Commission on Alcohol and Drug Abuse. The following information was taken from the report, ADWI Recidivism in Texas: 1985 through 1988" published by the Texas Commission on Alcohol and Drug Abuse.

Again, the conviction rate formula used was:

Conviction Rate = RC = Number of guilty dispositions / Number of all dispositions

The number of arrests state wide for 1985-1990 were obtained, and as shown below in Figure 2-7, fluctuated during that time period. However, the arrests are reported as a total by calendar year and so we were unable to perform additional calculations. (Arrests from one year may not be adjudicated until the following year or later.)

                      Figure 2-7: DWI Arrests In Texas, 1985 - 1990

Calculated Conviction Rates

The Texas Judicial Council provided monthly court data on the dispositions of DWI cases during the period January 1996 through October 1998. Available data did allow a determination or an estimate of the overall system conviction rate. Only conviction as a percentage of all disposed cases (RC) could be calculated. A total of 9,857 cases were disposed of during that period, an average of 290 per month or 3,479 per year. 6,917 of all dispositions were convictions, resulting in a conviction rate of:

RC = 6,917 / 9,857 = 0.702 = 70.2%

Figure 2-8 shows how this rate varied with month over the 34-month period. The highest conviction rate during this period was 79.7%, and the lowest was 61.6%.

Figure 2-8: Dwi Convictions as a Percentage DWI Dispositions in Texas, Rc - 1996 - 1998

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