GEOMETRIC DESIGN AND GENERAL FEATURES
GEOMETRIC DESIGN AND GENERAL FEATURES
- This section lays down the standards for geometric design and general features for the six-lane divided carriageway.
- Where there is a constraint of ROW width in built-up sections, the Authority may specify the construction of a bypass. The alignment of the bypasses shall be as specified in Schedule ‘B’ and in conformity with the site earmarked in
- Schedule ‘A’ of the Concession Agreement. Alternatively, the highway shall be elevated to a standard cross-section of six-lane and such elevated section shall be specified in Schedule ‘B’.
- The geometric design of the Project Highway shall conform to the standards set out in this section as a minimum.
- As far as possible, uniformity of design standards shall be maintained throughout the length of the Project Highway. In case of any change, it shall be affected in a gradual manner.
- Where the existing road geometries are deficient with respect to minimum requirements and its improvements to the prescribed standards are not feasible due to any constraint in the acquisition of additional land, such stretches shall be specified as a deviation in Schedule ‘B’ of the Concession Agreement.
The design speeds given in Table 2.1 shall be adopted for various terrain classification (Terrain is classified by the general slope of the ground across the highway alignment).
Short stretches (say less than 1 km) of varying terrain met with on the road stretch shall not be taken into consideration while deciding the terrain classification for a given section of Project Highway.
In general, the ruling design speed shall be adopted for the various geometric design features of the road. Minimum design speed shall be adopted only where site conditions are restrictive and adequate land width is not available. Such stretches where design speed other than ruling speed is to be adopted shall be specified as a deviation in Schedule ‘D’ of the Concession Agreement.
Right of Way
A minimum Right of Way (ROW) of 60 m should be available for the development of a 6-lane highway. The Authority would acquire the additional land required if any. The land to be acquired shall be indicated in Schedule ‘B’ of the Concession Agreement.
Where the alignment of 6-lane Highway is to be retrofitted on to existing highway, the details of ROW width on LHS and RHS from centre line of existing carriageway(s) at 50 m intervals shall be provided to the Concessionaire in Schedule ‘A’ of the Concession Agreement.
Lane Width of Carriageway
The standard lane width of the Project Highway shall be 3.5 m.
The median shall be either raised or depressed. The width of the median is the distance between the inside edges of the carriageway. The type of median shall depend upon the availability of the Right of Way. The minimum width of the median, subject to availability of Right of Way, for various locations, shall be as in Table 2.2.
The type and widths of median in various stretches of Project Highway shall be indicated in Schedule ‘B’.
The median shall have suitably designed drainage system so that water does not stagnate in the median. All median drains shall be of Cement Concrete.
In case of depressed median, a minimum 0.6 m width adjacent to carriageway in either direction shall be paved.
As far as possible, the median shall be of uniform width in a particular section of the Project Highway. However, where changes are unavoidable, a transition of 1 in 50 shall be provided.
In the case of the depressed median, metal beam type (Three beam – one-sided) crash barriers or Wire rope barrier shall be provided on either side of the median subjected to the requirements laid out in Section 9.7. Suitable shrubs as per Section 11 of this Manual shall also be provided. (In MORTH)
However, in case the width of median is more than 9 m, no crash barrier is required to be provided on the median side.
In case of median having width up to 2.5 m or paved medians, crash barriers and suitable antiglare measures such as plastic screens shall be provided at the centre of median, to reduce headlight glare from opposite traffic. The total height of screen including the height of the barrier shall be 1.5 m, and spacing shall be such as to effectively cut the glare. In case of unpaved median wider than 2.5 m suitable shrubs shall be planted as per Section 11 of this Manual.
Width of shoulders
The shoulder width on the outer side (left side of carriageway) shall be as given in Table 2.3 and 2.4.
- In case retaining wall with parapet is provided on valley side, the earthen shoulder may not be provided.
- Width of paved shoulder in approaches to grade separated structures as indicated in table above shall extend on either side of the structure up to a distance of 50 m or up to the end of retaining/RE walls (where walls are abutting the paved shoulder) whichever is more. The retaining/RE walls shall have crash barriers on top.
- In case retaining/RE walls are not abutting the paved shoulder the width of shoulder in the approaches to the grade separated structures shall be as for open country with isolated built up area beyond 50 m from the structure and flare of 1 in 25 shall be provided in the transition zone. Crash barrier shall be provided in the earthen shoulder.
Where embankment is more than 6 m high, kerb with channel shall be provided at the end of paved shoulder to channelize the drainage as an erosion control device in accordance with Section 6 of this Manual and earthen shoulder shall be raised up to the level of kerb.
The width of roadway shall depend upon the width of carriageway, shoulders and the median.
On horizontal curves with radius up to 300 m, width of pavement and roadway in each carriageway shall be increased as per Table 2.5.
The crossfall on straight sections of road carriageway, paved shoulders and paved portion of median shall be 2.5 percent for bituminous surface and 2 percent for cement concrete surface.
The crossfall shall be unidirectional for either side carriageway sloping towards the shoulder in straight reaches and towards the lower edge on horizontal curves. The camber on the existing road shall be modified to unidirectional crossfall.
The crossfall for granular shoulders on straight portions shall be at least 0.5 percent steeper than the slope of the pavement and paved shoulder subject to a minimum of 3 percent. On super elevated sections, the earthen portion of the shoulder on the outer side of the curve should be provided with reverse crossfall of 0.5 percent so that the earth does not drain on the carriageway and the storm water drains out with minimum travel path.
Geometric design shall conform to IRC:73, except as otherwise indicated in this Manual.
All horizontal curves shall consist of circular portion flanked by spiral transitions at both ends.
Super Elevation shall be limited to 7 percent, if radius of curve is less than desirable minimum radius. It shall be limited to 5 percent, if radius is more than desirable minimum.
Radii of horizontal curves
The desirable minimum and absolute minimum radii of horizontal curves for various classes of terrain are given in Table 2.6.
The radius of horizontal curves for various terrain conditions shall not be less than the desirable minimum values given in Table 2.6 except for sections as specified in Schedule ‘B’.
For such sections, the radius shall not be less than the absolute minimum.
The safe stopping sight distance and desirable minimum sight distance for divided carriageway for various design speeds are given in Table 2.7. The desirable values of sight distance shall be adopted throughout unless specified in Schedule B. As a minimum, safe stopping sight distance shall be available throughout.
The vertical alignment should provide for a smooth longitudinal profile. Grade changes shall not be too frequent as to cause kinks and visual discontinuities in the profile.
In this regard, directions given in IRC:73 shall be kept in view.
The ruling and limiting gradients are given in Table 2.8. Ruling Gradients shall be adopted as far as possible. Limiting Gradient shall be adopted in difficult situations and for short lengths.
Long sweeping vertical curves shall be provided at all grade changes. These shall be designed as square parabolas.
Design of vertical curves and their coordination with horizontal curves, shall be in accordance with IRC: SP:23.
Lateral and Vertical Clearance at Underpasses
Wherever a cross road is proposed to be taken below the Project Highway, minimum clearances at underpasses shall be as follows:
- Full roadway width of the cross road shall be carried through the vehicular underpass. The lateral clearance shall not be less than 1 2 m (7 m carriageway + 2 X 2.5 m shoulder width on either side) or as specified in Schedule ‘B’.
- For Light Vehicular Underpass the lateral clearance shall not be less than 10.5m including 1.5m wide raised footpaths on either side.
- For Pedestrian and Cattle underpasses, the lateral clearance shall not be less than 7m.
- Guardrails/crash barriers shall be provided for protection of vehicles from colliding with the abutments and piers and the deck of the structures.
Vertical clearance at Underpasses shall not be less than the values given below:
Wherever existing slab/box culverts and bridges allow a vertical clearance of more than 2 m, these can be used in dry season for pedestrian and cattle crossing by providing necessary flooring. However, these will not be a substitute for normal requirements of pedestrian and cattle crossings.
Lateral and Vertical Clearance at Overpasses
Wherever any structure is provided over the Project Highway; the minimum clearances at overpasses shall be as follows:
Full roadway width including service roads shall be carried through the overpass structure or as indicated in Schedule ‘B’. The abutments and piers shall be provided with suitable protection against collision of vehicles. Crash barriers shall be provided on abutment side and on sides of piers for this purpose. The ends of crash barriers shall be turned away from the line of approaching traffic. The span arrangement for the overpass structure shall be as specified in Schedule ‘B’.
A minimum 5 m vertical clearance shall be provided at all points of the carriageway and the service roads of the Project Highway.
Access to Project Highway
Access to the project highway shall be on the principle of left-in/left our arrangement and interconnected through underpasses, overpasses or grade separators. The considerations for planning, design and construction described in para 1.13 shall apply.
The roadway width of service road shall be minimum 10 m. In built-up areas where separator (as per para 2.15 of this Manual), between main carriageway and service road; and RCC/Cement Concrete lined drain-cum-footpath on ROW side are provided, no earthen shoulder shall be provided for service road. The minimum width of paved portion of the service road shall be 7 m. Any deviations to the above provisions shall be specified in Schedule ‘D’ of the Concession Agreement. Wherever required provision for Parking Bays of length 20 m and width 3.0 m may be made along the service road and the same shall be specified in Schedule ‘B’ of the Concession Agreement.
For the stretches where total length of a bridge is less than 60 m and the service road are required to be provided on both sides of the stream, then the service road shall continue across the stream and suitably designed 2-lane bridge structure shall be provided.
In cases involving bridges of 60 m length or more, separate bridge structures may not be provided and service road shall be merged with the Project Highway at 50 m distance before the bridge structure. Any deviation to this shall be specified in Schedule ‘D’.
Wherever service roads are provided, provision shall be made for proper entry and exit ramps between the main highway and the service roads through properly designed acceleration and deceleration lanes. The layout for entry/exit at service road shall be as per
Any deviations to these layouts due to site constraints shall be specified in Schedule ‘D’ of the Concession Agreement.
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