In the mid-1980s, acid rain and sudden forest destruction renewed debate on whether or not a general speed limit should be imposed on autobahns. A car's fuel consumption increases with high speed, and fuel conservation is a key factor in reducing air pollution. Environmentalists argued that enforcing limits of limit on autobahns and on other rural roads would save lives as well as the forest, reducing the annual death toll by 30% (250 lives) on autobahns and 15% (1,000 lives) on rural roads; the German motor vehicle death toll was about 10,000 at the time. The Federal Government sponsored a large-scale experiment with a speed limit in order to measure the impact of reduced speeds on emissions and compliance. Afterward, again, the Federal Government declined to impose a mandatory limit, deciding the modest measured emission reduction would have no meaningful effect on forest loss. By 1987, all restrictions on test sections had been removed, even in Hesse where the state government was controlled by a "red-green" coalition.