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Reliability Based Geometric Design of Horizontal Circular Curves

  • Pabitra Rajbongshi
  • Kuldeep Kalita
Original Contribution

Abstract

Geometric design of horizontal circular curve primarily involves with radius of the curve and stopping sight distance at the curve section. Minimum radius is decided based on lateral thrust exerted on the vehicles and the minimum stopping sight distance is provided to maintain the safety in longitudinal direction of vehicles. Available sight distance at site can be regulated by changing the radius and middle ordinate at the curve section. Both radius and sight distance depend on design speed. Speed of vehicles at any road section is a variable parameter and therefore, normally the 98th percentile speed is taken as the design speed. This work presents a probabilistic approach for evaluating stopping sight distance, considering the variability of all input parameters of sight distance. It is observed that the 98th percentile sight distance value is much lower than the sight distance corresponding to 98th percentile speed. The distribution of sight distance parameter is also studied and found to follow a lognormal distribution. Finally, the reliability based design charts are presented for both plain and hill regions, and considering the effect of lateral thrust.

Keywords

Horizontal curve Stopping sight distance Reliability 

List of symbols

ASD

Available sight distance (m)

ASDcal

Calibrated sight distance (m)

a

Deceleration of vehicle (m/s2)

COVX

Coefficient of variation (%) of random variable X

d

Distance between centre line of horizontal curve and inner lane

e

Super-elevation at the horizontal curve (%)

t

Perception reaction time of driver in s

f

Lateral coefficient of friction

fX(x)

Probability density function of random variable X

M

Middle ordinate at the horizontal curve section (m)

Pf

Probability of non-compliance

R

Radius of circular horizontal curve (m)

Re

Reliability

SSD

Stopping sight distance (demand) in metre

V

Mean speed of vehicular stream (kmph)

Vd

Design speed (kmph)

z

Standard normal deviate

\({\mathbf{N}}(z)\)

Probability corresponding to standard normal deviate z

\(\sigma_{X}\)

SD of random variable X

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Copyright information

© The Institution of Engineers (India) 2018

Authors and Affiliations

  1. 1.Civil Engineering DepartmentNational Institute of Technology SilcharSilcharIndia

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