Project 1 - Geometric Design Parameter- Prerequisites
1. The elements affecting the Road geometric design are listed and described below
a. Design Speed: It is the highest speed that a vehicle can travel on that road. Since the speed varies based on Vehicle type and driver, it is required to fix the Design Speed in such a way that it can satisfy all the vehicles and drivers types. It also depends upon Terrian. It directly effects Sight Distance, Horizontal Curve and Vertical Curve Design. 85th Percentile Design Speed is the maximum speed in a range where 85% of vehicles travels. A survey shall be conducted to collect the data of the speed of the vehicles and number of vehicles travels in that perticular speed to calculate the 85th Percentile Design Speed.
b. Topography: It is the 3D surface feature of the land. The differant types are Plain, Rolling, Hilly and Mountenous. This differentiation is based on the slope of the naural ground in a perticular strech, generally 1Km. It also effects the Design Speed, Cross Section of the Road, Carriageway width, Vertical and Horizontal Curve Design.
c. Design Vehicle: It consists of Standered Height, Weight and Operating Charecteristics. Carriageway width, gradient, turning radius, vertical clearance is effected by the Design Vehicle. IRC has standadise the Maximum laods based on the number of the axles and number of tyres. For example, Single Axle with Single tyres can carry up to 6MT. Single axle with duel tyres can carry upto 10.5MT. Tandam Axle with duel tyres can carry upto 18MT.
d. Human: The Driven and Pedestrian the humans effect the geometric design. The human charecteristics such as Age, reaction time, mood etc will influence the geometric design. The reaction time generally taken will be 1.5-2sec. However, as per IRC we will consider 2.5sec as the reaction time during design.
e. Environment: The situations when the Road traverses through Forest, Schools, Piligrim Centers etc will effect the Geometric Design. No Honking Zone, Speed Limit Zone are some of the examples.
f. Economy: The Road design shall be economical. Generally the Optimim design is prefered. The gemetric design will get changed based in the economy and feasibility.
g. Aestetics: Imporatance of Area, The Historical buildings, Nature etc.. plays an important role in the design of geometry. The length, width, Curve Design, Speed Limit etc.. will be influenced by this factor.
h. Traffic: The Traffic Volume and Capacity will effects the Geometric Design. The number of lanes will directly depends upon the Traffic Volume.