Hillsburgh and Nansensville are two major metropolitan areas only 50 miles apart. Until recently, the only road connecting the two cities was a traffic-clogged, six-lane Interstate Highway. Six years in the making, the Metro Expressway, a four-lane road connecting the two cities, was hoped to relieve this congestion. After the first month, however, the traffic along the Interstate Highway has not improved. Which of the following, if true, could account for the continued traffic congestion along the Interstate Highway?
【选项】The Metro Expressway opened up in July, a month when many of the citizens leave for vacation.