Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Gree...Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Greece is presented based on international research and an extensive drivers attitudes＇ survey. The 85th percentile speed has proven in this case to be the decisive criterion for establishing reliable speed limits or advisory speeds in most cases. The resulted 10 km/la increase in legal speed limits on freeways and express rural highways did not validate any fears that accident rates or frequencies would increase. On the contrary an 8% decrease of crashes was observed in a period of about three years after the implementation of the increased speed limits level on the rural highway network of the country.展开更多
Sites with varying geometric features were analyzed to develop the 85 th percentile speed prediction models for car and sports utility vehicle(SUV) at 50 m prior to the point of curvature(PC), PC, midpoint of a curve(...Sites with varying geometric features were analyzed to develop the 85 th percentile speed prediction models for car and sports utility vehicle(SUV) at 50 m prior to the point of curvature(PC), PC, midpoint of a curve(MC), point of tangent(PT) and 50 m beyond PT on four-lane median divided rural highways. The car and SUV speed data were combined in the analysis as they were found to be normally distributed and not significantly different. Independent parameters representing geometric features and speed at the preceding section were logically selected in stepwise regression analyses to develop the models. Speeds at various locations were found to be dependent on some combinations of curve length, curvature and speed in the immediately preceding section of the highway. Curve length had a significant effect on the speed at locations 50 m prior to PC, PC and MC. The effect of curvature on speed was observed only at MC. The curve geometry did not have a significant effect on speed from PT onwards. The speed at 50 m prior to PC and curvature is the most significant parameter that affects the speed at PC and MC, respectively. Before entering a horizontal curve, drivers possibly perceive the curve based on its length. Longer curve encourages drivers to maintain higher speed in the preceding tangent section. Further, drivers start experiencing the effect of curvature only after entering the curve and adjust speed accordingly. Practitioners can use these findings in designing consistent horizontal curve for vehicle speed harmony.展开更多
Vehicle operating speed is a crucial factor for road safety,as it strictly affects occurrence and severity of crashes.Usually,85th percentile of the operating speed distributions(i.e.,V85)in free-flow traffic conditio...Vehicle operating speed is a crucial factor for road safety,as it strictly affects occurrence and severity of crashes.Usually,85th percentile of the operating speed distributions(i.e.,V85)in free-flow traffic condition is widely accepted as a base value of consistency evaluation for homogenous portion of existing roads.Although the computation of V85 is simple,many road authorities cannot collect speed data for each road.Therefore,providing prediction models could be a useful tool to investigate the relationship between V85 and road characteristics.The literature proposed several models to account it.However,to the best of our knowledge,the effects of some road geometric characteristics,road markings and signs,traffic data,type of terrain and the simultaneous consideration of different road categories on the V85 prediction were not completely analyzed.This paper fills this gap by isolating key variables that mostly affect V85.In doing so,60000+car spot speed data were collected along the county road network of the province of Brescia(Italy),and then processed by multiple regression models.The main findings show that V85 increases owing to the presence of a wider or paved shoulder,visible road median markings,a higher number of lanes and a higher percentage of cars with respect to the total traffic flow.Conversely,V85 decreases as the road axis curvature,the number of accesses and rate of forbidden overtaking increase.In addition,the presence of visible road external markings and the surrounding mountainous terrain contribute to decreasing V85.The overall findings may support road authorities to verify roads’operating conditions and,possibly,adjust the speed limits,especially for existing roads.展开更多
文摘Setting reliable speed limits on roads has always been a challenging process of designers and road agencies. In this paper the results of a methodology for setting speed limits on rural roads of all categories in Greece is presented based on international research and an extensive drivers attitudes＇ survey. The 85th percentile speed has proven in this case to be the decisive criterion for establishing reliable speed limits or advisory speeds in most cases. The resulted 10 km/la increase in legal speed limits on freeways and express rural highways did not validate any fears that accident rates or frequencies would increase. On the contrary an 8% decrease of crashes was observed in a period of about three years after the implementation of the increased speed limits level on the rural highway network of the country.
基金Indian Institute of Technology Bombay for providing funding (Project code:13IRCCSG001)
文摘Sites with varying geometric features were analyzed to develop the 85 th percentile speed prediction models for car and sports utility vehicle(SUV) at 50 m prior to the point of curvature(PC), PC, midpoint of a curve(MC), point of tangent(PT) and 50 m beyond PT on four-lane median divided rural highways. The car and SUV speed data were combined in the analysis as they were found to be normally distributed and not significantly different. Independent parameters representing geometric features and speed at the preceding section were logically selected in stepwise regression analyses to develop the models. Speeds at various locations were found to be dependent on some combinations of curve length, curvature and speed in the immediately preceding section of the highway. Curve length had a significant effect on the speed at locations 50 m prior to PC, PC and MC. The effect of curvature on speed was observed only at MC. The curve geometry did not have a significant effect on speed from PT onwards. The speed at 50 m prior to PC and curvature is the most significant parameter that affects the speed at PC and MC, respectively. Before entering a horizontal curve, drivers possibly perceive the curve based on its length. Longer curve encourages drivers to maintain higher speed in the preceding tangent section. Further, drivers start experiencing the effect of curvature only after entering the curve and adjust speed accordingly. Practitioners can use these findings in designing consistent horizontal curve for vehicle speed harmony.
基金the research agreement research agreement signed in 2019 by the University of Brescia and the Province of Brescia(Prot.668/2019).
文摘Vehicle operating speed is a crucial factor for road safety,as it strictly affects occurrence and severity of crashes.Usually,85th percentile of the operating speed distributions(i.e.,V85)in free-flow traffic condition is widely accepted as a base value of consistency evaluation for homogenous portion of existing roads.Although the computation of V85 is simple,many road authorities cannot collect speed data for each road.Therefore,providing prediction models could be a useful tool to investigate the relationship between V85 and road characteristics.The literature proposed several models to account it.However,to the best of our knowledge,the effects of some road geometric characteristics,road markings and signs,traffic data,type of terrain and the simultaneous consideration of different road categories on the V85 prediction were not completely analyzed.This paper fills this gap by isolating key variables that mostly affect V85.In doing so,60000+car spot speed data were collected along the county road network of the province of Brescia(Italy),and then processed by multiple regression models.The main findings show that V85 increases owing to the presence of a wider or paved shoulder,visible road median markings,a higher number of lanes and a higher percentage of cars with respect to the total traffic flow.Conversely,V85 decreases as the road axis curvature,the number of accesses and rate of forbidden overtaking increase.In addition,the presence of visible road external markings and the surrounding mountainous terrain contribute to decreasing V85.The overall findings may support road authorities to verify roads’operating conditions and,possibly,adjust the speed limits,especially for existing roads.
