Variation in Free Flow Speed due to Roadway Type and Roadside Environment

This paper explores the effects of roadway and roadside environment characteristics on the speed chosen by drivers. This work is an observational study of 272 segments of two lane roads in Connecticut. Data was collected for lane width, shoulder width, road width, presence of curbs and edge delineation types. For the roadside environment the following variables were also measured: presence of sidewalks, building setback, driveway density and land use types. The sites were categorized into two roadway types of streets and highways, based on their physical form: edge delineation was the main differentiating characteristic. Free flow speed data was measured using hand held radar speed guns. The mean speed was used to represent the speed characteristics of the roadways. Analysis of variance was employed to identify significant variables in predicting mean speeds. Three separate models were estimated: streets, highways and combined for both streets and highways. The results of the analysis indicate that posted speed limit, land use type, roadway type, roadside parking and building setback are significant in influencing the mean free flow speed on roadway segments.