Semi-highway
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A semi-highway (also known as half-motorway or semi-motorway) is a grade-separated, controlled-access undivided highway which constitutes a single carriageway of a future full-profile highway while the second one is built. While physically similar to two-lane freeways, these roads are strictly built as temporary structures as a part of a freeway or highway in construction. Semi-highways can sometimes remain in the same state for long periods of time because of the high cost of building on certain terrain, such as in some parts of Switzerland. Sections of semi-highways are also frequently found in difficult terrain (where construction costs may be prohibitive), as a temporary and lower cost alternative to full construction. For example, instead of using two tunnel boring machines, one machine can excavate both without delaying the opening of the highway in either direction.

Examples of semi-highways

Most older highways in Croatia were originally built as semi-highways. A prominent example is the A6 highway, whose first roadway was completed in 2004. However, even after four years, the highway still has a 14 km (8.7 mi) long undivided section.² As of 2007, both roadways of new Croatian highways are constructed simultaneously, leading to a rapid decrease in semi-highway miles in the country. The Croatian Roads Authority announced that in the five years ending in 2005 450 kilometers (280 mi) of highways were built and an estimated 453 kilometers (281 mi) were being planned. In this same time frame 81 kilometers (50 mi) of semi-highways were completed, with 61 kilometers (38 mi) being planned.³

Several sections of German Autobahns have yet to be upgraded to full profile. The lower 100 km/h (62 mph) speed limit for undivided roads applies in derestricted speed zones, and passing may be permitted in the oncoming traffic lane. Examples include BAB 60 near the Belgian border and BAB 62 between Landstuhl and Pirmasens in Rhineland-Palatinate. In contrast, German federal highways (Bundesstraßen) are usually built as permanently undivided highways with frequent grade separations.

Newer Hungarian motorways are also built first as semi-highways and later completed. Examples are the M2 and M15.⁵ The M2 also features an unusual three-lane configuration.⁶ The M9 highway section connecting Szekszárd-Dombóvár in Transdanubia, Hungary will utilise 3 semi-highway sections during the construction process before achieving speedway status. Highway 66-611 will be modernized requiring a 15 kilometers (9 mi) section to initially start with the construction of a two-lane semi-highway. The aim is to increase road security reducing accidents and achieve status similar to the M65 highway.⁷

Swiss Autobahns are also sometimes built short of their design for topographical and financial reasons. The trans-Alpine A13 includes many tunnels and sections of semi-highway. These are similar to the Autostrassen, which are typically permanent structures.

Many toll roads in autopistas in Mexico are built in this way, often through difficult terrain.^{citation needed}

The Pan-European Corridor X in Serbia will utilise semi-highways until full funding and construction can be completed. 800 million euros is the initial investment for construction of Corridor X, however it is estimated that another 1.6 billion euros will be needed for the entire length of construction. At this initial stage it is projected that about of Corridor X through Serbia will be finished highway, and the remainder of the route will be semi-highway or local main roads.⁸

References

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