Central reservation
From Biocrawler, the free encyclopedia.
- For "central reservations" (such as for hotels), see call center.
On an expressway, motorway, or autobahn, the median (North American English) or central reservation (British English) is the strip of grass or the wall which separates opposing lanes of traffic. This is necessary because of safety concerns, due to the high speed of automobiles on both sides, and the potential danger of a disastrous head-on collision at the combined speed of both vehicles. Also the headlights of traffic in the opposite direction are less disturbing.
In North American cities, Jersey barriers are usually placed in the median to prevent head-on collisions.
Medians function secondarily as "green areas", beautifying roadways. Some jurisdictions mow their medians, others scatter wildflower seeds which germinate and re-seed themselves every year, while still others create extensive plantings of trees, shrubs, herbaceous perennials and decorative grasses. Where space is at a premium, dense hedges of shrubs filter the headlights of oncoming traffic and provide a resilient barrier.
The central reservation in the U.K. is usually no wider than a single lane of traffic. In some cases, however, it is extended; for instance, if the road is running through hilly terrain, the carriageways may have to be built on different levels of the slope. Two examples of this on the UK road network are on a section of the M6 between Shap and Tebay, where the carriageways are several hundred metres apart allowing a local road to run between them, and on the M62 where the highest section through the Pennines famously splits wide enough for a farm in the central reservation. The other major exception is the A38(M) Aston Expressway, which is a single carriageway of 7 lanes, where the median lane "moves" to account for traffic flow (a system known as tidal flow). Amazingly, there has never been an accident on this short stretch of road.
In North America, opposing lanes of traffic may be separated by several hundred meters of fields or forests outside of heavily populated areas, but converge to a lane's width in suburban areas and cities.ja:中央分離帯
