This is done by constructing a new road parallel to the existing two lane roadway and dividing northbound and southbound traffic with the use of a median. In areas with a concentrated population, twinning is often not feasible, because of the impacts to adjacent properties. Instead, both northbound and southbound lanes are constructed on a new alignment to minimize these impacts. Once the route selection planning process is complete, a variety of engineering activities must take place. The proposed highway corridor and service roads are carefully surveyed.
Geotechnical testing determines if the existing soils can support the highway and bridges.
The roadway and bridges are designed. Finally, property required for the construction of the highway is purchased. Proposed highway improvements are divided into projects to facilitate planning, design, and construction. After environmental approvals are received, another two to three years are required from the start of engineering work to the start of construction. Finally, each project takes, on average, two years to build.