Design of expressways
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The document provides guidelines for the design, planning, and construction of expressways, emphasizing safety, durability, and geometric design features such as carriageway width, median types, and access control. It details considerations for design speed based on terrain, horizontal and vertical alignment, underpasses, and overpasses, along with requirements for drainage, sight distances, and traffic circulation. Additional elements include suggestions on fencing, boundary stones, and pedestrian access, with a focus on maintaining efficient traffic flow and minimizing disruptions during construction.
Design of expressways
- 1. VIJAI KRISHNANV. M.Tech Student Transportation Engineering Rajiv Gandhi Institute ofTechnology, Kottayam, Kerala
- 2. DESIGN OF EXPRESWAYS General considerations for planning, design & construction 1. Carriageway provision & future widening 2. Safety of design 3. Durability 4. Mitigating disruptive effects of construction
- 3. 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
- 4. 2. Right of Way (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
- 5. 3. Land width of 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
- 6. 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 %
- 7. 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
- 8. 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
- 9. Decision sight distance 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%
- 10. Min. gradient for 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
- 11. 10. Underpasses Cross roads 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
- 12. 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
- 13. 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
- 14. Decision to construct 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
- 15. 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
- 16. 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