Speed limits in Germany
In 1973, in the wake of the 1973 oil crisis, a federal speed limit of 100 km/h (62 mph) on Autobahns was imposed to help conserve fuel for fear of impending future shortages (not for environmental or safety reasons). The measure only lasted from December 1973 to March 1974; while the administration and the Bundestag were in favor of keeping the speed limit, the Bundesrat pushed to repeal the law. As a compromise, a "recommended speed" was introduced on Autobahns and "highways outside of built-up areas with a center divide or without a center divide and a continuous lane for overtaking in both directions". This law is basically still in effect today. Unrestricted non-Autobahn highways, however, have since become virtually non-existent or replaced by "Schnellstraßen", Autobahn-like expressways typically limited to 120 or 130 km/h and normally only covering a few kilometers.
Speed limits in the United States by jurisdiction
Interstate Highways in Illinois are usually posted with both minimum and maximum speed limits, except in some urban areas, particularly Chicago. The standard speed limit is 70 mph for rural freeways, a 45 mph minimum speed limit, 65 mph for other 4 lane divided highways, and 55 mph for all other highways. Urban freeway/interstate speed limits can range from as low as 45 mph in downtown Chicago, where all the major interstates merge, to as high as 65 mph in the outer portions of the Chicago metro and East St. Louis metro areas, and in some smaller cities. Some interstates in small cities (e.g. I-55/74 through Bloomington-Normal, I-39/90 through the Rockford area, I-57 through Champaign-Urbana) do not have reduced speed limits, and a stretch of I-355 between I-55 and I-80 in the southwest suburbs of Chicago is signed at 70 mph. Most freeways and interstates in Cook, DuPage, and Lake Counties, and some interstates and freeways in Will County maintain a 55-60 mph speed limit. Due to the high population density, the only freeways in Cook County that exceed a speed limit of 60 mph are I-57 at the southern edge of the county, part of I-80 between Central Ave and Harlem Ave, I-90 west of Mt. Prospect Rd., and the southern segment of I-355, which passes through Cook County briefly before crossing into Will County to both the north and south. As of January 2010, a reduced speed limit posted in a construction zone must be obeyed 24 hours a day, regardless of whether workers are present.