Abstract
Several past studies developed acceleration/deceleration rate models as a function of a single explanatory variable. Most of them were spot speed studies with speeds measured at specific locations on curves (usually midpoint of the curve) and tangents to determine acceleration and deceleration rates. Fewer studies adopted an estimated value of 0.85 m/s2 for both deceleration and acceleration rates while approaching and departing curves, respectively. In this study, instrumented vehicles with a high-end GPS (global positioning system) device were used to collect the continuous speed profile data for two-lane rural highways. The speed profiles were used to locate the speeds at the beginning and end of deceleration/acceleration on the successive road geometric elements to calculate the deceleration/acceleration rate. The influence of different geometric design variables on the acceleration/deceleration rate was analysed to develop regression models. This study also inspeced the assumption of constant operating speed on the horizontal curve. The study results indicated that mean operating speeds measured at the point of curvature (PC) or point of tangency (PT), the midpoint of curve (MC), and the end of deceleration in curve were statistically different. Acceleration/deceleration rates as a function of different geometric variables improved the accuracy of models. This was evident from model validation and comparison with existing models in the literature. The results of this study highlight the significance of using continuous speed profile data to locate the beginning and end of deceleration/acceleration and considering different geometric variables to calibrate acceleration/deceleration rate models.
Highlights
Road infrastructure, vehicle, and human factors are the three concurrent factors causing road crashes [1, 2]
The values of the standard deviation are greater than the standard deviation of the field data. e values of MAD and RMSE are computed for all the models and tabulated in Table 13. e proposed model 1 for the deceleration rate in this study showed a very strong correlation, low errors, and variations (CRMS, RMSE, MAD, and SD) in comparison to all the other models compared
The study did not make any assumption about speed variation and the occurrence of maximum/minimum speed values at specific locations on the successive road geometric elements
Summary
Vehicle, and human factors are the three concurrent factors causing road crashes [1, 2]. Among these, operating speed measure is commonly used to develop speed profile models for the design consistency evaluation. Speed models along with the deceleration and acceleration rates when approaching and departing horizontal curves, respectively, are used in developing speed profiles for the design consistency evaluation of road segments [9]. Ere is a direct correlation between operating speed variability or deceleration/acceleration rates on consecutive road geometric elements and crash rate to evaluate geometric design consistency [23, 24]. E consistency index based on the inertial operating speed is another local design consistency evaluation method [9] In this method, operating speed and deceleration/acceleration rate models are required to construct operating speed and inertial operating speed profiles. Us, operating speed, deceleration, and acceleration rate models are required to construct the speed profiles in both local and global consistency models.
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