This sign has long been rejected since it is a direct and open suggestion that this behavior is acceptable. An unrealistically low speed limit can actually lead to accidents. Second, some drivers will obey the lower posted speed while others will feel it's unreasonable and simply ignore it. This disrupts the uniform traffic flow and increases accident potential between the faster and the slower drivers. Third, when traffic is traveling at different speeds, the number of breaks in traffic to permit safe crossing is reduced.
Pedestrians also have greater difficulty in judging the speed of approaching vehicles.
Many years of research have proven that lower speed limits do not appreciably alter traffic speeds. Tests have been conducted where the numbers on speed signs were arbitrarily raised or lowered to see what effect this would have on traffic. Speed checks before and after the change indicated that speeds remained very nearly the same regardless of the number on the sign. These studies indicate the validity of the assumption that drivers select their speeds intuitively based on the environment around them and the speeds with which they feel comfortable and safe. Other research studies have shown that speed limits set below the reasonable speed of the majority do not have significant effects on a reduction in the number of accidents on a road.