Twinning a road involves the construction of a similar or identical parallel road. It is usually done when an existing highway requires a significant increase in capacity. Twinning is frequently advantageous because it allows traffic capacity to be doubled and produces a

dual carriageway A dual carriageway ( BE) or divided highway ( AE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are ...

with separation between traffic directions, while keeping the existing

right of way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...

. Additionally, unlike simple widening, twinning has minimal construction impact for traffic on the old road while the twin is being built. Some freeways are constructed by bypassing an established two- or four-lane highway. The older highways, constructed before travel demand on those routes was high, or before the legislation of ''control of access'', are often lined with residences and businesses. Without control of access, a municipal or state government is obliged to provide a driveway access where the owner sees fit. In practice, road twinning projects typically have sections of new bypasses built around settlements (making twinning these sections impractical), while twinning is done in more rural areas. The bypass (or sometimes an entirely new highway) may be initially designed as a freeway, but often the need for such a route is not immediately present. Instead, a two lane road with no properties abutting it is constructed. A wide

right-of-way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...

is purchased in most cases so that enough property is available to simply ''twin'' the highway. These roads are known as a

Super Two A super two, super two-lane highway or wide two-lane is a two-lane surface road built to highway standards with wide lanes and other safety features normally present on a freeway with more lanes, typically including partial control of access, ...

, and can be easily upgraded to a freeway by constructing interchanges and by twinning the road. Twinning is often a public preference to reduce the dangers of overcrowded 2-lane single carriageways, like sections of the

Trans-Canada Highway The Trans-Canada Highway (Canadian French, French: ; abbreviated as the TCH or T-Can) is a transcontinental federal–provincial highway system that travels through all ten provinces of Canada, from the Pacific Ocean on the west coast to the A ...

.August 26, 2010
Fatal accidents prompt call for road twinning
CBC News.

References

Types of roads {{Road-stub