Median strip

Typical motorway road layout (Irish road markings)

The wide median strip in Main St, Bairnsdale, Victoria, Australia has been made into a garden feature of the town

For other uses, see Median strip (disambiguation).

On divided roads, including expressways, motorways, or autobahns, the central reservation (British English), median (North American English), median strip (North American English and Australian English) or central nature strip (Australian English) is the area which separates opposing lanes of traffic.

Some 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.

On British motorways the central reservation is never broken (except on the tidal flow of Aston Expressway), but there are no such restrictions on other dual carriageways. The medians of United States Interstate Highways break only for emergency service lanes, again with no such restrictions on lower classification roads.

The central reservation in the United Kingdom, and other densely populated European countries, 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 seven lanes, where the median lane "moves" to account for traffic flow (a system known as tidal flow).

In North America, and some other countries with large sparsely populated areas, 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. In urban areas, concrete barriers (such as Jersey barriers) and guard rails (or guide rails) are used. On arterial roads, traffic may be separated by landscaped medians, or by islands of concrete marked off with curbs; some U.S. states, such as California, have made such concrete islands more attractive by setting rocks in them.

One median of note is the "inverted" median of the Golden State Freeway (I-5) in the Tehachapi Mountains between Los Angeles, California and the San Joaquin Valley. For several miles the median is inverted — Northbound traffic is on the western roadway and southbound traffic on the eastern road.

Safety

An August 1993 study by the U.S. Federal Highway Administration quantified the correlation between median width and the reduction of both head-on accidents and severe injuries. The study found that medians without barriers should be constructed more than 30 feet (9.1 m) in order to have any effect on safety, and that safety benefits of medians increase to a width of 60 feet (18.3 m) to 80 feet (24.4 m). A consequence of this finding is that decreasing the size of a median to 20 feet (6.1 m) from 30 feet (9.1 m) to add lanes to a highway may result in a less safe highway. Statistics regarding medians with barriers were not calculated in this study.

Trivia

Concrete median barrier near Dublin, Ireland

A California arterial road median with rocks set in it

• The median for Canal Street in New Orleans (and by extension, for all streets in Greater New Orleans) is called "neutral ground" by local residents. (See: Regional vocabularies of American English.) This term stems from the city's early years. The American newcomers and the Creole old timers didn't get along with each other, and divided generally with Americans upriver from Canal Street and the Creoles downriver (in today's French Quarter). The wide area in the middle of Canal Street (where the canal was never dug) became known as the neutral ground, where members of the groups could transact business or otherwise mingle.