Driver safety is one of the major concerns of traffic engineers while designing and constructing highways. Highway accidents lead to both social and economic losses. Accident rates on horizontal curves are higher than those on tangent sections. Studies on safe geometric design have hypothesized constant acceleration/deceleration along the curve for all types of curve geometry. Which is far from reality, where drives choose acceleration/deceleration based on their perceived road geometry rather than actual geometry provided. In addition, available models on acceleration/deceleration have concentrated only on two-lane bi-directional traffic. Thus, there is a need to study and develop models on acceleration/deceleration behaviour for other road types.
To develop acceleration/deceleration models, road geometry data and vehicle acceleration/deceleration data were collected. The vehicle acceleration/deceleration data were obtained from Video V-Box vehicle average speed data. Road geometry were obtained by extracting V-box data into Auto CAD. The V-Box data were collected from multiple drives over a 30 km stretch, on a four-lane highway (NH-3) in mountainous terrain. The 30 km stretch covers a wide range of geometry. The stretch has a gradient ranging from −5% to 5%, curve radius and curve length are up to 200 m. With this data, models were developed both for acceleration and deceleration of vehicles. These developed models are found to be satisfactory on validation. From this study it was also found that the acceleration/deceleration values obtained were not constant over the horizontal curve in mountainous terrains. The deceleration values exhibited a strong relationship with the approaching tangent length, and the acceleration values depended on the length of the departure tangent. Furthermore, both acceleration and deceleration depended on geometric parameters such as the radius and gradient of the curve. Using these developed models, designer can improve the safety of the curve geometry on the basis of the driver’s acceleration/deceleration behaviour.
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