Three college professors were driving down the highway at a very slow speed. A policeman pulled them over and explained that driving so slowly on the highway could be hazardous. The driver pointed out the sign that read "20." He explained that he was going 20 mph because of the sign. The policeman pointed out that the sign indicated they were driving on Highway 20. Somewhat embarrassed the professor apologized and promised to be more observant. As the policeman turned to walk back to his car, he noticed the other two professors on the floor ...looking scared to death! He asked the driver, "What's wrong with them?" The driver replied, "We just turned off Highway 105."