[If you drink, don't drive: drunk drivers in Guadalajara and León, Mexico].

Objectives: To estimate the percentage of drivers of motor vehicles under the influence of alcohol circulating during Thursday, Friday, and Saturday night in the metropolitan areas of Guadalajara (municipalities Zapopan and Guadalajara) and León, Mexico, together with their blood alcohol content. To evaluate the impact of the Mexican Initiative for Road Safety (IMESEVI, Phase I) in this respect.

Material And Methods: Drivers who were stopped at sobriety checkpoints during the three above-mentioned nights were given an alcohol test together with a brief questionnaire that asked for sociodemographic and other background variables. The study made use of a pre-post design, with data collections at the start of IMESEVI (June 2008) and a year and a half later (February 2010) in the metropolitan areas of Guadalajara and León. A random sample of 1,299 (pre) and 2,226 (post) drivers participated in the study. The data analysis was based on a hierarchical logistic model for ordinal dependent variables.

Results: At baseline, the breathalyzer showed a positive result in between 17% (Zapopan) and 29% (León) of the drivers, while between 1-3% exceeded the legal maximum of 0.08 g/dl for blood alcohol content in Mexico. The night of observation, the presence of passengers in the vehicle, as well as the driver's civil state and sex affected the probability of a positive result. At the post measurement, the probability of a positive result decreased to about a third of the baseline measurement.

Conclusions: In view of the evidence that links alcohol with the probability of being involved in an accident, drinking and driving prevention programs may contribute significantly to better road safety in Mexico.