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Copy of HIGHWAY PLANNING
Transcript of Copy of HIGHWAY PLANNING
Factors to be considered during planning
How will the proposed project affect the general physical character of the area surrounding the project ?
Coordination with Utilities
P. Vipul Naidu
The entire length of expressway has a single layer of barbed wire fencing to keep out stray cattle.
DEFINITION OF TERMS
THE DESIGN SPEED
CROSS SECTION OF TYPICAL HIGHWAYS
THE CROSS SLOPE
CUT OR FILL SLOPE
NUMBER OF LANES
THE GRADE LINE
VERTICAL CURVE OVER CREST
RIGHT OF WAY
STOPPING SIGHT DISTANCE
THE PASSING SIGHT DISTANCE
WIDENING OF CURVES
TYPES OF INTERCHANGE
HIGHWAY INTERSECTION AT GRADE
FREEWAY ENTRANCE AND EXIT
-the most important single rule in highway design
Drivers expect the highway agency to provide them with:
DEFINITION OF TERMS
ROADS AND HIGHWAYS
CONTROL OF ACCESS
FULL CONTROL OF ACCESS
PARTIAL CONTROL OF ACCESS
THROUGH STREET OR THROUGH HIGHWAY
CROSS SECTION of TYPICAL HIGHWAY
variables to consider such as:
(1) the volume of traffic
(2) character of the traffic
(3) speed of the traffic
(4) characteristics of motor vehicles and of the driver
A cross section design generally offers the expected level of service for safety and a recent study shows that:
A 7.20 meters wide pavement has 18% less accident compared with pavement narrower than 5.50 m wide.
A 7.20 meters wide pavement has 4% fewer accidents than the 6.60 m wide roadway.
Accidents records showed no difference between 6.60 meters and the 7.20 m wide pavement.
For the 6.00 m,6.60 m, and 7.20 m wide pavement with 2.70 to 3.00 m wide shoulder, recorded accident decrease by 30% compared to 0 to .60 m wide shoulder. And 20% compared with a .90 to 1.20 m wide shoulder.
cross section for:
two lane rural highways
local rural highway
Importance of road shoulder
Policy on Geometric design
Importance of Road Shoulder
Policy on Geometric Design Recommendation
Vertical Curve Over Crust
" The vertical distance fro the intersection of the straight grade line to the curve is equal to the curve is equal to one eight of the product of the algebraic difference in grades andthe length of the curve in stations."
Right of Way
Acquisition of land for the right of way is very costly.
Stopping Sight Distance
It is defined as the longest distance that a driver could see the top of an object 15 cm above the road surface where the design height of the driver's eye above the pavement is 105 cm.
uphill or downhill:
The Passing Sight Distance
It is defined as the longest distance that a driver can see the top of an oncoming vehicle where the driver's eye level is 1.05m above the pavement surface.
L = 2S - 943
L = 2AS
- should be consistent
- abrupt change from flat to sharp curve should be avoided
- designing circular curves of different radius is not a good practice
- having a short tangent between two curves is a poor practice
HIGHWAY INTERSECTION AT GRADE
1. For right angle intersection with little traffic, use street signs.
2. For Y intersection or other related conformation, requires channelization.
3. For flared design will involve:
a. Widening the entering traffic lane
b. Widening the leaving lanes
4. Must accomodate large trucks.
Freeway Entrance and Exit
Overall effectiveness is governed on:
1. Flow characteristics of vehicles
2. Driver's behavior near on and off the channel
Single lane on ramp vehicle:
- design is either taper blending
- sufficient length is required
Railroad - highway Separation
- requires minimum of 7 meters as against 4.8 meters clear distance above the highway
- requires special provision when highways are under railroads
- design speed is 20 to 30 km/hr
- width is 2 meters (minimum) for two way travel
- grade is 5% (maximum) on short distances
The sharpness of a curve is dependent on its radius.Sharpness is expressed in terms of the curve degrees, and the degrees of curve is inversely proportional with the radius.
Arc Definitions-the degree of curve is the central angle subtended by a 30 m arc of the curve
Chord Definitions-the degree of curve is the central angle subtended by 50 m chord
sin (1/2) D
Widening of Curves
A provision for a wider roadway is necessary on a sharp curve for two lanes pavement under the ff. reasons:
1.) Two force drivers to shy away from the pavement edge.
2.) To increase the effective transver se vehicle width for non-tracking of front and rear wheels.
3) To give additional width due to the slanted position of the front wheel to the roadway center line.
4) For a 7.20 meters wide roadway, an additional width of 30 cm is necessary on an open curve highway.
An island is a defined area between traffic lanes for control of vehicle movement and for pedestrian refuge.
It is included in the design of intersections for the following purposes:
Separation of vehicular flows.
Separation of conflicts.
Reduction in excessive pavement areas.
Reduction of traffic and indications of proper use of intersections.
Arrangement to favor a prominent turning movement.
Location of traffic control devices.
TYPES OF INTERCHANGE
To facilitate the easy transfer of vehicles from one entry to the other or between local roadway and the freeway.
The types and form of freeway interchange requires selection of the conformation that is best suited to a particular situation and demand. The functions of freeway interchanges are:
To provide separation between two or more traffic arteries.
Objections to the Cloverleaf Interchange Design
The Cross Slope
a cross slope in one direction of multi lane highways makes driving comfortable, with heavy rainfall, the water depth increases on the highway.
Cut or Fill Slope
Earth fill of normal height is safe on the slope of 1:2 ratio.
Advantages of Flat Side or Back Slope
With back slope of 3:1 o even flatter, cars could be directed to back into the road and will come to stop or continue down the slope with no risk of over turning.
Flat fill slopes are visible from the vehicles at full extent giving the roadway safer appearance.
With visible slope for being low and flat, vehicles could be positioned closer to the edge, and on two lane roadway facilities parking would be farther from the opposing traffic.
Recommended Policy on Geometric Design
The 6:1 Slope ratio could be adopted on embankment less than 1.20 meters high, and 4:1 ratio on a higher fill.
The 2:1 slope is allowed to heights greater than 6.00 meters.
Cut slope should not be steeper than 2:1 ratio except on solid rock or special kind of soil.
Stipulated that where cut or fill slopes intersects the original ground surface, cross section must be rounded to blend the slope with the natural ground surface.
Materials could be used when the slide slope requires embankment:
Hand placed stones
Cement rubbles masonry
Conventional reinforced concrete
T or counter forted designs
Cribs assembled from timber
Number of Lanes
The number of lanes in the segment of the highway is determined from the estimated traffic volume for the design year (AADT) and highway lane capacity at expected level of service.
median in various forms, becomes absolute requirement for highways because it offers many advantages.
For narrow median, there are four means of reducing cross median accidents.
Provide deterring devices
Provide non-traversable energy absorbing barriers
Provide non-traversable rigid barriers.
Provide G.M. barriers
In flat area, the grade line is set almost parallel to the ground surface but sufficiently above the ground for drainage purposes.
Undesirable native soil should be provided with sufficient covering.
Grade line elevations along the river or stream, is governed by the expected level of water flood.
In laying the grade line, the designer must consider the following:
Where earthwork is minimal and consistently meeting sight distances in relation to grade line, economy is one main consideration
In mountainous area, the grade line must be considered balanced excavation against embankments to get the minimum overall cost