Stergios Mavromatis

Investigation of vehicle motion on sharp horizontal curves combined with steep longitudinal grades

The research addresses the safe negotiation of sharp horizontal curves combined with steep longitudinal grades. Instrumented field measurements were carried out utilizing a FWD C-Class passenger car in both upgrade and downgrade directions of travel. Initially, the vehicle was driven in braking mode on adjacent steep grade tangent sections in order to define the peak friction coefficients. During vehicle’s tractive mode, for various speed values, friction data were measured and correlated against a vehicle dynamics model developed by the authors’ as well as the point mass model, in order to examine the interaction between vehicle dynamics and road geometry in such alignments. The findings regarding vehicle speed prediction revealed that the dynamic model, on both upgrades and downgrades, is accurate. On the other hand, the point mass model although more simple, revealed accuracy, of a smaller degree, however, but only on upgrades. Moreover, certain findings are reported among which the fact that steep upgrades are more critical at impending skid conditions as well as the acceleration impact in vehicle’s safety.

Analytical Method for 3-D Stopping Sight Distance Adequacy Investigation

The adopted 2-D SSD (stopping sight distance) adequacy investigation in current design practice may lead to design deficiencies due to inaccurate calculation of the available sight distance. Although this concern has been identified by many research studies in the past, none of them suggested a comprehensive methodology to simulate from a 3-D perspective concurrently both the cross-section design and the vehicle dynamics in space during emergency braking conditions. The proposed methodology can accurately perform SSD adequacy investigation in any 3-D road environment where the ground, road and roadside elements are inserted by identifying areas of interrupted vision lines between driver and obstacle being less than the required distance necessary to bring the vehicle to a stop condition. The present approach provides flexibility among every road design and/or vehicle dynamic parameter inserted, as well as direct overview regarding design elements that restrict the drivers vision and create SSD inadequacies. As a result, precious guidance is provided to the designer for further alignment improvement but mostly an accurate aid to implement geometric design control criteria with respect to both existing as well as new road sections is delivered. The efficiency of the suggested methodology is demonstrated through a case study.

Stopping sight distance adequacy assessment on freeways: the case of left horizontal curves over crest vertical curves

ABSTRACT This paper investigates potential Stopping Sight Distance (SSD) violation on divided highways at left horizontal curves overlapped with crest vertical curves. The authors previously developed a SSD control methodology that relates the 3D configuration to the dynamics of a vehicle moving along the roadway. This methodology is applied for the assessment of critical design parameters related to both demanded and available SSD values. Initially, utilizing control geometric and driver – obstacle values adopted by AASHTO 2011 design policy, SSD inadequacy areas were revealed. Subsequently, on the basis of an explanatory modeling approach for a number of geometry parameters, evaluation of SSD sufficiency was carried out in terms of the probability of SSD inadequacy and the prediction of the object height in order to grant SSD adequacy (amended object height). These models may be useful to researchers and practitioners aiming to evaluate the interaction of the utilized design parameters in terms of SSD inadequacy.

Safety assessment of control design parameters through vehicle dynamics model

An existing vehicle dynamics model was utilized to define design parameters up to which steady state cornering conditions apply and consequently lift the restrictions of the point mass model. Aiming to assess critical safety concerns in terms of vehicle skidding, the motion of a passenger car was examined over a range of design speed values paired with control design elements from AASHTO 2011 Design Guidelines as well as certain values of poor pavement friction coefficients. Two distinct cases were investigated; the determination of the maximum attainable constant speed (termed as safe speed) at impending skid conditions as well as the case of comfortable curve negotiation where lower constant speed values were utilized. The overall objective was to define the safety margins for each examined case. From the interaction between road geometry, pavement friction and vehicle characteristics, many interesting findings are reported, where some of them are beyond the confined field of road geometry parameters; such as demanded longitudinal and lateral friction values and horse-power utilization rates. From the road geometry point of view, it was found that control alignments on steep upgrades consisting of low design speed values and combined with poor friction pavements are critical in terms of safety. Such cases should be treated very cautiously through certain actions. These actions include the adoption of acceptable arrangements for the above values regarding new alignments, posted speed management for existing but also scheduling friction improvement programmes more accurately for both cases.

Vehicle Skidding Assessment through Maximum-Attainable Constant-Speed Investigation

AbstractAn existing vehicle dynamics model was used to define design parameters up to which steady-state cornering conditions apply and consequently lift the restrictions of the point mass model. B...