Factor Controlling The Geometric Design

*The geometric layout of highways offers with the size and format of seen functions of the motorway. The emphasis of the geometric layout is to cope with the requirement of the motive force and the motors together with safety, comfort, efficiency, etc.

*Geometric design of highway deals with the following elements. Cross-section elements. (Width of pavement,
formation, and land, etc.,), Sight-distances, Horizontal alignment details, Verticals alignment details, Intersection elements, Design speed, Gradient, etc.


  • DESIGN SPEED: This is the most important factor controlling the geometric design elements. It is decided on the basis of the type of road or class of roads such as NH, SH, MDR, etc. and topography of the region.

Speed is a parameter that has a large variant will the man or woman driving, the car type, the topography, etc. This is the motive why the layout pace is taken as a number one component withinside the geometric layout of highways. The maximum non-stop pace, for the reason that the climate situations are conducive, to facilitate protection traveling of the automobiles is known as the layout pace. The legal pace isn’t like the layout pace. The felony pace is the velocity at which the drivers have a tendency to tour past a secure pace. The desired pace is the most pace at which the driving force can tour whilst they’re limited by way of a neighborhood geometry or traffic. As cited before, pace is a component that delivers versions of various types. This calls for having exceptional car layout speeds to fulfill the requirement of all car drivers. So, with the aid of using the standard: 85th percentile layout pace is the typically followed layout pace. 85th percentile layout pace may be described as the velocity that’s better than pace taken with the aid of using 85% of the drivers on that road. For a few nations, this cost may be withinside the variety of ninety-five to ninety-eight percentile pace.

  • Topography: Design pace or ruling pace of NH and SH on specific terrains is as follows. (a) Plain terrain (go slope as much as 10%)-100kmph (b) Rolling terrain (go slope of 10% to 25%) 80kmph (c) Mountainous terrain (go slope of 25% to 60%)-50kmph
  • Traffic factors: These include
    (a) Vehicular characteristics.
    (b) Road user characteristics.

It can be uneconomical to layout the street for top visitors’ flow. Therefore an affordable cost of visitors quantity is chosen because the layout hourly quantity that is decided from the diverse visitors records collected.

  1. Design Hourly Volume and capacity: It is uneconomical to design the road facilities for the peak traffics flows, hence a reasonable value of traffic volume is decided for the design which is called the design hourly volume.


Friction between the wheel and the pavement surface is an important factor in design.

The approach of the technique consists of full-scale experiments at the British Road Research Laboratory’s tune the use of braked and rolling wheels beneath neath cautiously managed situations, laboratory investigations of the viscoelastic houses of rubber together with rubber friction tests, and theoretical considerations linking the different factors.

layout automobile which has widespread weight, dimensions, and working traits are used to set up motorway layout controls to deal with motors of a delegated type. The dimensions, weight of the axle, and operating characteristics of the vehicle influence the design aspects such as the width of the pavement, radii of the curve, clearances, parking geometric, etc.

  • I.R.C. recommends the longitudinal friction coefficient values of 0.35 to 0.40 and lateral coefficient of friction of 0.15.
  • A skid happens whilst the wheels slide without revolving or whilst the wheels in part revolve i.e. whilst route traveled alongside the street is extra than the circumferential motion of the wheel.
  • A slip occurs when the wheel revolves more than the corresponding movement along the roads.

Factors affecting friction :

Different aspects of tread pattern design and tread material are considered in relation to factors external to the tire, the major ones being the influence of water depth over a range representative of conditions on the road, the interaction of road surface texture, and the effect of speed.

The object of the investigations described in this paper is to put in perspective the relative roles of the “drainage” and “energy loss” properties of tires in providing good adhesion on wet roads. This work has to result in a higher information of the mechanism of tire/avenue adhesion on moist surfaces and specifically to attract the difference among, and relative significance of, lubrication and aquaplaning.

(i) Type of pavement surface and conditions of pavement for e.g. wet or dry smooth or rough etc.
(ii) Type and condition of the tyre.
(iii) The temperature of tyre and pavement.
1. The coefficient of friction decreases with increases in temperature, tyre pressure and load. Smooth and worn out tyre offer higher friction factors on dry pavements than new tyres with treads due to large areas of contact, but on wet pavements, new tyres have higher friction factors.

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