Design Standard Consideration
Amongst the major design elements that shall be adopted are as follows :
- Design Speed - The design speed of the expressway shall be 100km/hr
- Geometric Elements - The minimum horizontal radius shall be 525m. However lower radius and design speed shall be considered where the constraints are not permitted.
- Verticle Grades - A maximum of 4% grade shall be limited to the mainline and 6% on the ramps. The minimum grade shall be taken at 0.5% generally. The minimum clearance shall be 6.5m height.
- Cross Section Elements - Typically, the traffic lane shall be 3.75m width. Paved shoulder shall be provided along the mainline with a 3.0m width. For an at-grade section, 1.2m green verge will also be provided to facilitate signages and other expressway furnitures such as emergency telephones.
- Pavement - The pavement shall be from a flexible pavement with a design life of 10 years. The design loadings for the pavement will be based on the 12 tones axles to cater for freight traffics
- Bridge Loading - All bridge’s loading for dead, live and collision loads shall be referred to British Department of Transport BD37/88 and shall be checked with British Standard BS5400: Part 2
- Surface Drainage - The surface drainage shall be designed to 2 year return period fro roadside drain and 5 years for roadside culvert. The minimum size of pipe culverts crossing the road shall be 750mm diameter in sizes to ease maintenances. The return periods for the drainage structures are 100 years for bridges and a minimum of 50 years for box culverts
- Geotechnical Design - The cut slope adopted shall be 1V:1.5H and the fill slope shall be 1V:2H with a maximum berm height of 4.5m and 6.0m respectively
The allowable embankment settlement shall be 250mm whilst for structure’s piles shall limit to 6mm. Other geotechnical design shall be considered as required to improve ground conditions such as vertical drain, remove and replace and slope protection as where required