ABSTRACT
The main concurrent factors on road safety are: the driver, the vehicle and the infrastructure. Infrastructure factor is present in the 30 % of accidents in rural roads. One of the main reasons related to this factor is the low consistency of road geometric design. That produces that road alignment doesn’t fit drivers’ expectations. Thus, number of accidents may be increased.
For road design consistency evaluation, the most used criteria are based on the evaluation of operating speed profile. Operating speed is defined as the 85th percentile of speed distribution developed by vehicles driving in free flow conditions along a road segment. This variable may be obtained by means of data collection during road operation phase. However, during planning and design phases, it only can be estimated by models as a function of road design geometric characteristics. In this research work, different models have been calibrated. The combination of those models, by means of construction rules, allows the estimation of continuous operating speed profile of a two-lane rural road segment, as a function of its alignment.
A new data collection methodology has been developed. It is based on data recorded by GPS devices placed on the vehicles of drivers who don’t know the research objectives. Data collection results include drivers’ individual continuous operating speed profiles and their trajectories. Data treatment allows the restitution of road alignment and the corresponding continuous operating speed profile.
Besides of the calibration of models for the estimation of continuous operating speed profile, speed distributions on curve and tangent sections have been studied. Speed variation phenomena on tangent-to-curve-to-tangent transitions have also been deeply studied.
The calibrated models may be used on road safety evaluation, not only during planning and design phase before choosing final solution, but also during operation phase. This way, it becomes on a key tool for the evaluation of one of the most important concurrent factor: infrastructure.
However, it is also important to include in the study the other two factors: human factor and vehicle. This study has been carried out focusing on the relationships between the characteristics of driver, its trip and its vehicle type, and the developed speeds on tangent and curves sections and deceleration and acceleration rates.
This study has provided conclusions that may be used as the base of the design of education programs and awareness media campaigns related to road safety.