Geometric Design of Road

The geometric design of highways is the branch that is concerned with the physical element & positioning of roadways according to standards.The objective is to minimize cost & ensure high safety.

TYPES OF ROAD CAMBERS

• WIDTH OF PAVEMENT/CARRIWAGE

1. Width of pavement depends upon traffic lane & Number of lane

2. The portion of carriageway that is intended for one line of traffic movement is called a traffic lane.

3. Width of the traffic lane is decided on the basis of the vehicle width

4. Passenger car is a standard vehicle to decide the width of carriageway

5. For rural highway if it has single lane the length is 3.5m

6. No of lanes to be provided depends upon traffic volume

Width of different carriageways are as follows:

• GUARD RAILS

These are provided at the edge of the shoulder when the road is constructed on a fill so that vehicles are prevented from running off the embankment,especially when height of fill is more than 3m.

• FOOTPATH/SIDE WALKS

In order to provide safe facilities to pedestrians to walk along the road, footpath walks are provided in urban areas,where pedestrian traffic is more.

Its minimum width required is 1.5m & desirable minimum length is 2m.It is also provided with a cross slope of 2.5-3% & given comparatively smoother surface then pavement.

• DRIVE WAY

It connects the highways with local commercial establishment places,service stations,fuel stations,restaurants etc.

• CYCLE TRACK

These are provided in urban areas for safe movement of cycle traffic.The minimum width required is 2m for cycle track & it is increased by one m each for additional cycle lane

• PARKING LANES

These are provided on urban roads to provide kerb parking.

As far as possible only parallel parking should be allowed as it is safer for moving vehicles & space required would be less.

For parallel parking the minimum width required is 3m

• BUS BAYS

It may be provided by accessing the kerb to avoid the conflict with the moving traffic & must be located at least 75m of location away from interaction.It is used for safe movement of passengers and cargo from buses.

• LAY BYS

These are provided near public convenience,to avoid the conflict between the running traffic minimum width is 3 meter.

• FRONTAGE ROADS

These are provided to give access to properties along the highways to control excess to the expressways.

• ENVIRONMENTAL SLOPE

If pavement is constructed over embankment slopes are also provided along it of magnitude 1 in 3.