High-Beam Usage on Low-Volume Rural Roads in Texas

Abstract

This study evaluated high-beam usage on low-volume roadways in Texas. Most previous studies used a subjective approach to determine high-beam usage that involved a stationary observer or an observer driving around the study section. For more efficient data collection, this study used photometric readings as the methodology. This approach allowed for a quantitative measure of high-beam use, in that it did not rely on an observer's opinion as to whether the headlamps were on high or low beam. Preliminary data collection was conducted as part of the study to estimate the threshold high-beam illuminance value; these illuminance data showed moderate use of high beams on low-volume, rural two-lane highways, with 42% of the free-flow drivers using high beams. There was a wide variation in high-beam use between sites, so site characteristics were reviewed to identify potential reasons for this variation. The data were fit to a logistic regression model to estimate the impact of various site characteristics on a driver's decision to use high beams. The results showed that vehicle speed, paved surface width, number of access points within 1,000 ft of the site, and presence of horizontal curves within 1 mi of the site were statistically significant factors that contributed to the probability of high-beam use. The results also showed that higher vehicle speeds, narrow paved surfaces, presence of horizontal curves, and few or no access points led to a higher probability of high-beam use. These results are intuitive and support the observations made in the exploratory data analysis.