Temporary Roads – Design Considerations

Temporary roads are regularly required on construction sites. Also known as temporary haul roads, they provide access basically for heavy construction vehicles carrying materials and equipment needed to complete the project.

Although an access road may only be needed for a short period, but it’s design should be based on relevant standards, so that it can carry the anticipated traffic load over the operational life without being damaged or deteriorated significantly.

The temporary road design will take several factors into account. A few important ones are summarised below:

• Existing ground strength—normally expressed as a California Bearing Ratio (CBR), undrained shear strength or stiffness modulus
• Anticipated traffic load—expressed as a number of vehicle visits of differing type and configuration (e.g., concrete mixers, delivery vehicles) from which a number of Equivalent Standard Axle Loads (ESAL’s) can be calculated
• Number of lanes required, single carriageway or dual carriageway depending on the volume of traffic the road is expected to take
• Design speed and posted speed
• Topographical survey data of the area

Geometry of Roads

The geometry of roads should be according to standards relevant to the design speed. The geometric design of temporary roads will like the design of new roads. Abrupt, sharp curvature in the transition area from the existing highway to the temporary road is to be avoided. Clear sight distance to the stop signs or traffic signal, on the approach to these traffic control devices, is essential. Sight distance and adequate length of roadway to bring a vehicle to a complete stop from its operating speed must be provided. Any vertical curves must provide headlight stopping sight distance to satisfy this requirement. The entire length of the temporary road, between the stop signs, should be visible to a driver stopped at the stop sign. Pavement widths may have to be widened, through horizontal curves, to provide adequate turning radii for trucks.

Other considerations

• Need for relocation of existing underground or overground utilities
• The environmental issues such as noise, air quality, landscaping, heritage, existence of protected species etc. ?
• Drainage requirement and type of drainage system to be provided
• Provision of road markings and signs
• Preparation of appropriate typical cross sections in cut and fill conditions
• Side slope of embankment depending upon the height and type of soil
• Provision of guard rails for embankments
• Provision of guard rail/VCB in case of two-way carriageways
• Materials to be used e.g., granular layers, asphalt surfacing over granular layers
• Need for signal control
• Provision of adequate shoulder with adequate construction to cater the needs of broken-down vehicles etc.
• Safety consideration during construction, operation, maintenance and dismantling
• Lighting requirements
• Flood risk assessment
• Installation of electronic traffic control devices
• Temporary bridges/culverts and their robust design
• Soil stabilisation for improving the load bearing capacity of native soil/embankments
• CCTV cameras for ensuring implementation of posted speed limit of the road

Sustainability Consideration

• Performance based design of subbase using secondary materials.
• Use of warm asphalt instead of hot asphalt
• Use of low heat cement or Blast Furnace Slag instead of cement
• Using LED lights for street lighting
• Use of solar panels for lit up signs

Use of geogrid/geosynthetics in subbase layers:

Many temporary access roads are needed where existing ground conditions are poor as well as variable. Often, this means that using “traditional methods”, these roads could require a significantly thick layer of stone to cater for the anticipated traffic load and will often need regular maintenance to address surface deformation and rutting.

Stabilisation geogrids can give road designers and users significant benefits in terms of reducing the thickness of the granular layer needed to build the road. This results in:

• Reduced construction cost
• Reduced construction time
• Reduced environmental impact.

Quality Control

The materials’ testing from the certified labs is important. The samples should be collected by authorised person and sealed before sending them to the labs. The required in-situ testing during construction is also required to undertaken by competent staff.

Potential for Re-Using and Recycling of Temporary Roads

The re-use and/or recycling of materials used in the temporary roads should be considered and planned. Even the temporary roads could be used as future cycle lane.?