Project 1 - Geometric Design Parameter- Prerequisites

Q-1: HIGHWAY ELEMENTS REQUIRED FOR GEOMETRIC DESIGN : Followings are the parameters which are required for geometric design ;

• Geometry Control Factors
• Design Speed
• Topography
• Traffic
• Design Vechile
• Enivironment
• Human
• Economy
• Aesthatics

a - GEOMETRY CONTROL FACTORS : Geometry of a highwaydepends on varoius factors and each factor has a important and major role in design of a safe geometry, aesthatically good and driver friendly highway.

INPUTS OUTPUTS

1. Safety & mobility for all Design speed

2. Quality of life & public health objectives Design hour

3. Economic sustainability Design year

4. Enviromental sustainability Design vehicle

b - DESIGN SPEED :

• Design speed is the most important geometry control factor.
• It is directly linked to sight distance, horizontal curve and vertical curve.
• The speed of a vehicle vary with respect to type of vehicle, driver and terrain condition.
• Design speed is defined as the highest speed a vehicle can travel on the road when the conditions are smooth.
• Since the speed varies with respect to different vehicles and drivers, the design speed should be selected in a way to satisfy all the vehicles, driver types and also based on the terrain condition.
• Speed of the road depends upon the requirement and the purpose it is been used
• When roads are planned, the selected design speed may be based on or influence several factors including the geometric design of road features and planned operating speed.

SPEED LIMITS AT DIFFERENT ROADS

TYPE OF ROAD	DESIGN SPEED ( kmph)
	PLAIN AREA		ROLLING AREA		HILLY AREA		STEEP AREA
	ROLLING	MINIMUM	ROLLING	MINIMUM	ROLLING	MINIMUM	ROLLING	MINIMUM
National Highway and State Highway	100	80	80	65	50	40	40	30
Major District Roads	80	65	65	60	50	40	40	30
Other District Roads	65	50	50	40	30	25	25	20
Village Roads	50	40	40	35	25	20	25	20

** 85th PERCENTILE DESIGN SPEED : The 85th percentile speed is the speed at or below which 85% of the drivers travel on a road segment. Driver travelling the 85th percentile speed are considered to be exceeding the safe and reasonable speed for road and traffic condition.

To find out 85th percentile speed , we must have 2 important criteria;

1 . Speed of vehicles

2 . Number according to the speeds

By the graph of Cummulative % frequency and Speed of vehicles : we will take speed relative to 85% of cummulative frequency, called as 85th percentile speed

c - TOPOGRAPHY : Topography is a 3D representation of the surface features of the land. It will impact other factors like design speed and cost.

Based on topography condation, terrain is classified into followings:

a- Plain terrain : slope having 0 to 10%

b- Rolling terrain : slope having 10 to 25 %

c- Mountainous terrain : slope having 25 to 60 %

d- Steep terrain : slope having greater than 60%

d - TRAFFIC : It will be unfair and also uneconomical to design the road for a peak traffic flow.Hence, a reasonable traffic flow is considered in the design based on the estimation carried out after various traffic surveys. Thus the geometry of the road depends upon the design volume and the capacity of traffic.

e - DESIGN VEHICLE : Design vehicle consists of standard weight, dimension and operating characteristics which influence the gradient, turning radius, width of carriageway, the clearence requirement and geometry features. The design vehicle will be applicable in designing all the types of roads.

The commercial vehicles have been recognized in 3 categories;

a- Single unit

b- Semi trailer

c- Truck trailer combination

The selection depend upon terrain condition, economic justification and impoprtance of road.

MAXIMUM PERMISSIBLE GROSS WEIGHT & MAXIMUM AXLE WEIGHTS OF TRANSPORT VEHICLES

VEHICLE TYPE	MAXIMUM GROSS WEIGHT (tonnes)	MAXIMUM AXLE WEIGHT (tonnes)
		TRUCK / TRACTOR		TRAILER
		FRONT AXLE WHEEL	REAR AXLE WHEEL	FRONT AXLE WHEEL	REAR AXLE WHEEL
TYPE-2 (both axles singe tyre)	12	6	6
TYPE-2 (single axle dual tyre )	16.2	6	10.2
TYPE-3	24	6	18(tandem axle)
TYPE-2-S1	26.4	6	10.2		10.2
TYPE-2-S2	34.2	6	10.2		18(tandem axle)
TYPE-3-S1	34.2	6	18(tandem axle)		10.2
TYPE-3-S2	42	6	18(tandem axle)		18(tandem axle)
TYPE-2-2	36.6	6	10.2	10.2	10.2
TYPE-3-2	44.4	6	18(tandem axle)	10.2	10.2
TYPE-2-3	44.4	6	10.2	10.2	18(tandem axle)
TYPE-3-3	52.2	6	18(tandem axle)	10.2	18(tandem axle)

f - ENVIRONMENT :

The factors like the forest area and noise pollution will play a role in the geometry of the road.

In the noise restricted zone like school zones we should not have too many curves and have better visiblity.

The geometry of the forest area road has to be planned in such a way we avoid disturbance to flora and fauna and also social places like religious worship places.

g - HUMAN :

Human behaviour as aroad user in the form of driver and also as pedestrians need to be considered.

The reaction time of the driver, the behavior and mental conditions of pedestrians crossing the road also influence the geometry.

h- ECONOMY :

This always plays a major role in deciding the geometry.

The road designed are to be economical as far as possible.

It should match with the funds planned including the other costs like maintanance.

i- AESTHETICS :

Aesthetics also play a major role in defining the geometry of the road and the importance of a area, the histrorical buildings, and nature everything.