Exploring the Relationship between Roadway Characteristics and Speed Variation

The degree of roadway service quality can be effectively related to individual vehicles’ degree of speed variation observed over roadway segments. In previous studies, the degree of speed variation, measured from the speed profiles of individual vehicles, has been proposed as a potential traffic parameter that may be effectively used to quantify driver, roadway, and traffic condition interactions. However, these relationships have not yet been extensively investigated because of the difficulty in collecting speed profile data. This study explores the relationship between acceleration noise–a speed variation measure defined as the standard deviation of the acceleration of a vehicle–and roadway characteristics. Data were gathered with the use of instrumented vehicles equipped with global positioning systems. The vehicles travel a freeway corridor over a 3-month period. Utilizing random intercept models that account for correlations from repeated measurements, the effects of roadway characteristics on acceleration noise are examined for each level-of-service condition. For the corridor studied, the results indicate that acceleration noise and thus the traffic conditions experienced by the driver are affected by the number of lanes, the speed limit, the facility type, and, to a lesser degree, by roadway curvature and grade.