Project 1 - Geometric Design Parameter- Prerequisites

Project-1

Que 1: List all the highway elements required for Road Geometric Design as prerequisite & necessary checklist during design. eg. Design Speed, Design Vehicle etc.. Explain in Detail 300 Marks

Ans 1:

Geometric design of highways: The highways crosses section element

1. Camber
2. Sight distance
3. Type of sight distance
4. Design of horizontal alignment
5. Superelevation
6. Widening of pavement on horizontal curves
7. Transition curve
8. Design of political alignment
9. Gradient summit and valley curves

Importance of geometric design:

Geometric design of a highway deals with the dimension and layout of visible feature of the highways such as horizontal and vertical alignment, sight distance and intersection. The geometric of highway should be designed to provide efficiency in traffic operations with maximum safety and reasonable cost. The designer may be exposed to either planning of new highway network or improvement of existing highway to meet the requirements of the existing and the anticipated traffic. Geometric design of highway deals with the following elements.

1. Cross section elements
2. Sight distance considerations
3. Horizontal alignment detail
4. Vertical alignment details
5. Intersection elements

Under cross section element the consideration for the width of pavement formation and land, the surface characteristic and cross slope of pavement included the site distance or clear distance visible ahead of a driver at horizontal and vertical curves and at intersection govern the safe movement of vehicles

Design control and criteria

The geometric design of highways depends on several design factors the important factor which control the geometric elements are

1. Design speed
2. Topography or terrain
3. Traffic factor and Design Vehicle
4. Design hourly volume and capacity
5. Environmental and others factor
6. Sight Distance

Design speed:

The design speed is the most important factor controlling the geometric design element of highways. The design speed is decided considering the overall requirements of the highway. In India different speed standard have been assigned depending upon the importance or the class of the road such as National Highway, State Highways, major or other district routes and village roads. Further the design speed standards are modified depending upon the terrain or topography. Similarly, urban roads have different set of design speed.

Topography;

The topography or the terrain condition influenced the geometric design of highway significantly. The terrain are classified based on the general slope of the country across the alignment as plain rolling mountainous and steep terrain. the design standards specified for different classes of roads are different depending on the terrain classification.

for example, the design or rolling speed of NH&SH on plane terrain with general cross slope up to 10% is 100 kilometer per hour whereas the speed on rolling terrain with general cross slope of 10 to 25% is 80 kilometers per hour and that on mountainous terrain with cross slope 25 to 60% is 50 kilometers per hour. As the speed standards affect the geometric design element topography also affects the geometric design of the road further in hilly terrain it is necessary to allow for steeper gradient and sharper horizontal curves due to the construction problems.

Traffic factors and Design Vehicle;

The factors associated with the traffic that affect the geometric design of road or the vehicular characteristic and human characteristic of road users it is difficult to decide the design vehicle or the standard traffic lane under the mixed traffic flow condition prevalent especially on urban roads of developing countries like India this is a complex problem.

the different vehicle classes such as passenger cars buses trucks motorcycles and various other types of non-motorized vehicles how different speed and acceleration characteristic apart from having different dimensions and weights.

Design hourly volume and capacity;

The traffic flow or more volume keeps fluctuating it's the time from a low value during certain off-peak hours to the higher flow during the peak hours. It will be uneconomical to design the roadway facilities for the peak traffic flow or the highest early traffic volume therefore a reasonable value of traffic volume is decided for the design and this is called the design hourly volume this value is to be determined from extensive traffic volume studies.

Environmental and other factors;

The environmental factors such as aesthetics, landscaping, air pollution, noise pollution and other local conditions should be given due consideration in the design of road geometrics. some of the arterial high-speed highway and Expressway are designed for highways higher speed standards and uninterrupted flow of vehicles by providing controlled access and grade separator separated intersection.

Sight Distance:

Sight distance one of the important factor on which safe and efficient operation of vehicle on roads depends is the road length when an obstruction if any becomes visible to the driver in the direction of travel in other words the distance visible ahead to the driver is very important for safe vehicle operation on a highway side distance is the length of the road visible ahead to the driver at any instance side distance available at any location of the carriage wing is the actual distance a driver with his high level at the at a special specified height above the pavement surface as visibility of any stationary or moving object of specified height which is on the carriageway ahead

Check list During Design:

1. This checklist should be used during the development of the geometric plans for highway projects
2. This checklist is to be used in conjunction with the most current versions of the Highway Design Manual or IRC codes.
3. Some items in the checklist may not apply to every
4. Answered with "no" require an explanation in the space below the question and, if deviations from standards result, the appropriate approvals are to be obtained and the engineering decisions documented appropriately.
5. Design features or elements that deviate from IRC standards require approval of the Chief, Division of

Design Speed:

IRC should be read before selecting a design speed. Design speed selection will affect sight distance, vertical alignment, horizontal alignment, and other requirements. Based on engineering judgement, projects with multiple roadways may require more than one selected design speed.

1. Proposed design speed for project
2. Minimum Design Speed for this type of facility
3. Design Speed of the roadway segment prior to project
4. Design Speed of roadway segment after project
5. Posted speed (for existing facilities)
6. Operating speed (85^th percentile or observed) (for existing facilities)
7. Does the design speed comply with concerned standard code?
8. Does the design speed meet or exceed the posted and operating speeds?

Design Period

Has a period of specified years after completion of construction been selected as the design period for new facilities and reconstruction projects?

Pedestrian Facilities

1. Have suitable pedestrian facilities been provided for anticipated pedestrian demand that is based on existing and projected land uses?
2. Do all proposed pedestrian facilities comply with IRC standard
3. Do sidewalk widths meet or exceed minimums?
4. Are Kerb ramps or blended transitions serving each pedestrian crossing?
5. Are ramps and/or kerb openings provided at midblock crosswalks and where pedestrians cross kerbed channelization or median islands?

Design Vehicle Selection

Design vehicle been selected in accordance with IRC?

Fencing

Have fencing or other approved barriers been installed on all newly acquired controlled access?

Bike

Have appropriate bicycle facilities been included if part of the regional?

Geometric Design Criteria:

Vertical Alignment

Sight Distance Criteria:

1. Has the project sustained downgrades steeper and longer than specified standard ? If yes, has the design stopping sight distance in IRC table.
2. Does each crest vertical curve provide the minimum stopping sight distance related to design speed as indicated in IRC table.
3. At each grade, sag, does the length of vertical curve provide headlight sight distance? If no, has lighting been considered as mitigation?

Grade Standards:

1. Does the entire profile grade comply with the maximum grades specified IRC?
2. Does the profile grade exceed the minimum grades of 5% for snow country and 0.3% at other locations?
3. Are ramp grades less than or equal to 8 percent; or 9 percent if descending on-ramps or ascending off-ramps?

Vertical Curve Criteria:

1. Do the lengths of the vertical curves equal or exceed
2. if the design speed is ≥40 kmph and algebraic grade difference comply with IRC
3. if design speeds are <40 mph or algebraic grade difference is comply with IRC
4. On 2-lane highways, are the crest vertical curves comply with IRC in length?

Horizontal Alignment

1. Do all the curve radii exceed the minimum values listed as per IRC for the appropriate superelevation rate and design speed?
2. Is the minimum stopping sight distance listed as per IRC provided at each horizontal curve for the appropriate design speed?
3. If central angle is less than specified degrees as per IRC, is the curve length greater?
4. Is the curve length on 2-lane roads between specified value in IRC?

Superelevation

1. Have the superelevation rates specified in the IRC been used for all horizontal curves?
2. On rural 2-lane roads, is the standard superelevation rate carried across the full width of the traveled way and shoulders, except on transitions?
3. Has adverse superelevation been avoided in warping street or ramp surface areas for drainage?
4. For undivided highways, has the axis of rotation been selected to improve perception of curves (i.e. on desert highways) and to avoid drainage pockets at superelevated highway sections (which usually occur in flat terrain)?
5. For divided freeways and conventional highways, has the axis of rotation been selected with consideration of aesthetics, grade distortion, superelevation transitions, drainage and driver perception?
6. Does two-thirds of each superelevation runoff length occur on the tangent which precedes or follows the curve, and does one-third occur within the curve?
7. Are the superelevation transitions for the project avoiding the bridges?
8. Are the superelevation transitions for compound curves, if used on the project, designed in accordance with IRC specification?

Right of Way:

1. If the project requires right of way acquisition, have future project needs and the ability to meet all design standards, without exceptions, been taken into consideration during the establishment of the new right of way lines for this project?
2. Have stormwater storage and treatment features been incorporated? Are they within the right of way?

These are some checklist during consider during highway design