Freeway Free Flow Speed: a Case Study in Italy

Results are presented relative to an experimental investigation regarding the speeds implemented on motorways in free flow conditions. The results demonstrate that the maximum speed, in free flow conditions, is to be found on flat straight stretches, with a section width of around 11 meters. In such conditions the free flow speed (FFS) is found to be at values of around 131 km/h. Such a speed tends to decrease when some of these conditions vary. In particular the dimensions which influenced the FFS are: slope, curvature, tortuousness and the width of the section. The lowest FFS value was encountered in ascent (+4,5%), on a straight stretch, section width of around 9 meters and tortuousness degree equal to 21 degrees/Km; in these conditions the FFS is found to be around the value of 105 km/h. These results consented the forming of the first consideration for the identification of the structure of the model for speed estimation, implemented by drivers, on the motorway in free flow conditions. It is believed that this information could be extremely useful in the evaluation of the level of service (LOS) in the motorway field.

[1]  Joseph Fazio,et al.  Estimating Free-flow Speed from Posted Speed Limit Signs , 2011 .

[2]  Gianluca Dell’Acqua,et al.  Speed Factors on Low-Volume Roads for Horizontal Curves and Tangents , 2010 .

[3]  Renato Lamberti,et al.  Models of Operating Speeds for Low-Volume Roads , 2011 .

[4]  Richard Jon Porter.  Estimation of relationships between 85th percentile speeds, speed deviations, roadway and roadside geometry and traffic control in freeway work zones , 2007 .

[5]  Gianluca Dell’Acqua,et al.  Road Performance Evaluation Using Geometric Consistency and Pavement Distress Data , 2011 .

[6]  Mario De Luca,et al.  Road Safety Knowledge-Based Decision Support System , 2011 .

[7]  Bin Nie,et al.  Modeling Driver Speed Behavior on Horizontal Curves of Different Road Classifications , 2007 .

[8]  Fred L. Mannering,et al.  MODELING THE ENDOGENEITY OF LANE-MEAN SPEEDS AND LANE-SPEED DEVIATIONS: A STRUCTURAL EQUATIONS APPROACH , 1998 .

[9]  Mario De Luca,et al.  Before-After Freeway Accident Analysis using Cluster Algorithms , 2011 .

[10]  L. Kinderytė,et al.  Methodology of Sustainability Indicators Determination for Enterprise Assessment , 2010 .

[11]  Eric T. Donnell,et al.  Some New Insights on Design Consistency Evaluations for Two-Lane Highways , 2010 .

[12]  Gianluca Dell’Acqua.  Reducing Traffic Injuries Resulting from Excess Speed , 2011 .

[13]  Wayne A Sarasua,et al.  Posted and Free-Flow Speeds for Rural Multilane Highways in Georgia , 1999 .

[14]  Raffaele Mauro,et al.  Speed Prediction Models for Sustainable Road Safety Management , 2011 .

[15]  Gianluca Dell’Acqua,et al.  Safety Performance Functions for Low-Volume Roads , 2011 .

[16]  Mario De Luca,et al.  Motorway Speed Management in Southern Italy , 2011 .