directions are permitted to use the lane for passing. In a similar layout, three lanes are striped with two in one direction and one in the other, but traffic in the direction with one lane is allowed to cross the centerline to pass. 2+1 roads have replaced some of these, mainly in Europe. Turn lanes and flush medians Another type of center two-way lane is a "two-way left turn lane" (TWLT) or "center left-turn lane", or (for countries that drive on the right) "center turn lane" or "median turn lane", a single lane in the center of the road into which traffic from both directions pulls to make a left turn. This lane is also sometimes called a "suicide lane" for their notorious fatality rates, especially in the United States in settings with high traffic speeds (45 mph), and on roads with five or more lanes (typically two or three lanes in each travel direction with one center turn lane). However, some studies have found that converting high-speed four lane streets into three lane streets (one lane of traffic in each direction with a center turn lane) and lowering speed limits can result in improved safety, despite the use of a center turn lane, as traffic collisions occur at far lower speeds. These roads are very common in suburban areas and less common in rural areas, though they are frequent around developed areas near Interstate Highway bypasses in the United States. Many were divided highways before the median was demolished or otherwise replaced by the turn lane. Many four-lane streets with a center double yellow line are being phased out in favor of 3- or five-lane streets with center turn lanes because the center lane allows for less disruption of traffic flow. For routes with moderate traffic, other movements involve downgrading four-lane undivided streets to three-lane streets with a turn-only center lane. This center lane can be used by emergency vehicles like police cars, ambulance, and fire trucks to avoid traffic traveling in either direction. Drivers are not allowed to use the center lane of such a highway for passing slow-moving vehicles, except when funding or space constraints dictate use of it as a rush hour "travel lane" when traffic is largely asymmetric between a central business district and its suburbs. U.S. Route 13 near the Greenville, North Carolina, city limits is a rare instance of a posted warning sign