1950s, with reports of increasing numbers, some permits to capture devils were granted after complaints of livestock damage. In 1966, poisoning permits were issued although attempts to have the animal unprotected failed. During this time environmentalists also became more outspoken, particularly as scientific studies provided new data suggesting the threat of devils to livestock had been vastly exaggerated. Numbers may have peaked in the early 1970s after a population boom; in 1975 they were reported to be lower, possibly due to overpopulation and consequent lack of food. Another report of overpopulation and livestock damage was reported in 1987. The following year, Trichinella spiralis, a parasite which kills animals and can infect humans, was found in devils and minor panic broke out before scientists assured the public that 30% of devils had it but that they could not transmit it to other species. Control permits were ended in the 1990s, but illegal killing continues to a limited extent, albeit "locally intense". This is not considered a substantial problem for the survival of the devil. Approximately 10,000 devils were killed per year in the mid-1990s. A selective culling program has taken place to remove individuals affected with DFTD, and has been shown to not slow the rate of disease progression or reduced the number of animals dying. A model has been tested to find out whether culling devils infected with DFTD would assist in the survival of the species, and it has found that culling would not be a suitable strategy to employ. Road mortality Motor vehicles are a threat to localised populations of non-abundant Tasmanian mammals, and a 2010 study showed that devils were particularly vulnerable. A study of nine species, mostly marsupials of a similar size, showed that devils were more difficult for drivers to detect and avoid. At high beam, devils had the lowest detection distance, 40% closer than the median. This requires a 20% reduction in speed for a motorist to avoid the devil. For low beam, the devils had the second shortest detection distance, 16% below the median. For avoidance of roadkill to be feasible, motorists would have to drive at around half the current speed limit in rural areas. A study in the 1990s on a localised population of devils in a national park in Tasmania recorded a halving of the population after a hitherto gravel access road was upgraded, surfaced with bitumen and widened. At