Design of expressways

Design of expressways

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  VIJAI KRISHNANV. M.Tech Student TransportationEngineering Rajiv Gandhi Institute ofTechnology, Kottayam, Kerala
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  DESIGN OF EXPRESWAYS Generalconsiderations for planning, design & construction 1. Carriageway provision & future widening 2. Safety of design 3. Durability 4. Mitigating disruptive effects of construction
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  Geometric Design &General Features 1. Design Speed  Terrain varying for short stretch < 1km is not considered  Speed limit should justify - Economy - Environment - Driver Expectancy Terrain Cross Slope Design Speed (km/h) Plain < 10 % 120 Rolling 10 – 25 % 100 Hilly/Mountainous > 25 % 80
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  2. Right ofWay (ROW)  Min. right of way in Plain/Rolling terrain  Additional land required – grade separated structure – interchange – toll plaza – bridge approach  No service road permitted within ROW Section ROW width Rural 90 – 120 m Semi-rural passing through semi – urban areas 120 m
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  3. Land widthof carriageway  Standard lane width = 3.75 m  Min no. of lane in one direction = 2 4. Median  Depressed or flush  Edge strip of 0.75 m  Max. ht of flush median = 1.5m  Uniform width & anti-glare measures  Designed drainage system for depressed median Type Min.Width Desirable Depressed 12 m 15 m Flush 4 – 5 m 4.5 m
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  5. Shoulders  Width= 3m paved + 2m earthen  Composition & specification same as carriageway  Earthen shoulder thickness = 200mm (granular/non-erodible) 6. Roadway Width  Depend on carriageway width, shoulders & median 7. Camber/Cross fall  Unidirectional C/s element Annual Rainfall  1000mm  1000mm Carriageway,paved shoulder,edge strip, flush median 2.5 % 2.0 % Granular/earthen shoulder on straight portion  3.5 %  3.0 %
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  8. Horizontal alignment Largest practical radius  Circular with spiral transition at both ends  Radius of horizontal curve (R)  Shall not be less than absolute min. radius  Super elevation  Limited to 7%, if R < desirable min. radius 5%, if R > desirable min. radius Design Speed Abs. Min. Radius Desirable Min. Radius 120km/h 670m 1000m 100km/h 440m 700m 80km/h 260m 400m
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   Transition Curve Sight Distance  Min. of SSD shall be available throughout Design Speed (km/h) Min. length of transition curve (m) 120 100 100 85 80 70 Design speed(km/h) SSD Desirable min SSD (ISD) 120 250m 500m 100 180m 360m 80 120m 240m
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   Decision sightdistance  Provided at critical locations or decision points where change in c/s occur (toll plaza, intersections etc...) 9. Vertical Alignment  Grade change shall not be too frequent Design speed(km/h) Decision Sight Distance 120 360m 100 315m 80 230m Terrain Ruling Gradient Limiting Gradient Plain 2.5% 3% Ruling 3% 4%
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   Min. gradientfor drainage – 0.5% (lined side drain) - 1.0% (unlined)  Vertical curves  Designed as square parabola (summit & valley curves)  Length depend on Sight Distance  Curve with longer length is desirable  Avoid sharp horizontal curve at/near apex of summit/sag curve  Avoid superimposing short/long vertical curve on long/short horizontal curve Design Speed Min. grade change Min. length* 120km/h 0.5% 100m 100km/h 0.5% 85m 80km/h 0.6% 70m
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  10. Underpasses  Crossroads are taken below expressways  Provide crash barriers for protection from collision with abutments, piers & deck of structures 11. Overpasses  Structure is above expressway  Min. vertical clearance at all points – 5.5m Underpass type Min. Lateral Clearance Min.Vertical clearance Vehicular 12m 5.5m Light vehicular 10.5m 3.5m Pedestrian 7m 3.0m
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  12. Access Control Access  Full access control for fast motorized traffic  Provided with grade separation at intersection  Parking/standing, loading/unloading of goods & passengers, pedestrian/animals – not permitted  Location of Interchange  At crossing/nearest points of - Expressways, NHs, SHs & important arterial roads and major roads to – Ports - Airports - commercial & industrial areas - places of tourist interest
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   Connecting Roads For proper circulation of local traffic  Continuity of travel  To facilitate crossing over to other side of expressways through under or overpass  Fencing is provided  Width = 7m 13. Grade separated structures  Approach gradient < 2.5%  Intersection where parallel cross roads are located within 2km, design as staggered crossing  In built-up areas, expressway is elevated on viaduct
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   Decision toconstruct a grade separated structure is taken based on - Drainage - Land acquisition - Height of embankment - Provision of ramp - Project economy  Structure is decided to be underpass/overpass based on:- - Nature of terrain -Vertical profile of road - availability of adequate sight distance
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   Pedestrian Underpass/overpass Max. distance to reach crossing facility = 500m  Provided within 2 km of vehicular under/overpass & 200m from school/hospital/factory/industrial area  Provision for disabled persons 14. Median Opening  Provided at 5km spacing with detachable barrier  Should not be located on curves & closer than 450m from any structure/speed change taper
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  15. Fencing &Boundary Stones  Fencing - at 2m inside of ROW boundary - Height = 2.5m - Made of mild steel & welded steel wire mesh - Fencing post is embedded in M15 concrete - Anti-corrosive paint on exposed metal surface  Boundary stones - to demarcate ROW - spacing = 100m - made of cement concrete - painted with cement primer & enamel paint