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 or reversible lane). With effect from January 2005 and based primarily on safety grounds, the UK's Highways Agency's policy is that all new motorway schemes are to use high containment concrete step barriers in the median (central reservation). All existing motorways will introduce concrete barriers as part of ongoing upgrades and through replacement as and when the current systems have reached the end of their useful life. This change of policy applies only to barriers in the median of high speed roads and not to verge side barriers. Other routes will continue to use steel barriers. 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 (an extreme example being the Trans-Canada Highway near Ernfold, Saskatchewan, Canada, where eastbound and westbound lanes go as far as apart from each other), but converge to a lane's width of separation in suburban areas and cities. In urban areas, concrete barriers (such as Jersey barriers) and guard rails (or guide rails) are used. In Dedham, Massachusetts, the Norfolk County Correctional Center (a state prison) is located entirely within a wide median of Massachusetts Route 128. This 502-bed facility was opened in 1993 as infill construction in the previously unused real estate that had been isolated by the divided highway in the early 1950s. An extreme example of a wide median can be found on Interstate 75 near Cincinnati, Ohio; nearly the entire village of Arlington Heights, as well as the downtown district of Lockland, are both located between the two directions of I-75. Inverted median Some freeways in North America include "inverted" medians, which separate roadways running in the opposite direction from the standard for the country they are located in. Roads are so designed for a number of reasons, including to save space or for the creation of continuous flow intersections. The north–south Golden State Freeway (I-5) in the Tehachapi Mountains of California between Los Angeles and the San Joaquin Valley. For several miles, the direction of traffic on both sides of the median is reversed — northbound traffic is on the western roadway and southbound traffic on the eastern roadway. I-85