On divided roads, including expressways, motorways, or autobahns, the central reservation (British English), median (North American English), or median strip (North American English and 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 population 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 of the most famous medians is the famous "inverted" median of the Golden State Freeway (I-5) in the rugged Tehachapi Mountains between Los Angeles, California and the San Joaquin Valley. For several miles of the freeway, the median is inverted — that is, northbound traffic is in the western roadway, and southbound traffic is in the eastern road.

Trivia

• 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, immediately after the Louisiana Purchase of 1803. 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 two groups could transact business or otherwise mingle, if they chose.

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