A research study revealed that, in most cases, once existing highways near urban areas are widened and extended in an attempt to reduce traffic congestion and resulting delays for motorists, these problems actually increase rather than decrease. Which one of the following, if true, most helps to explain the discrepancy between the intended results of the highway improvements and the results revealed in the study? ['Urban traffic generally moves at a slower pace and involves more congestion and delays than rural and suburban traffic.', 'Typically, road widening or extension projects are undertaken only after the population near the road in question has increased and then leveled off, leaving a higher average population level.', 'Widened and extended roads tend to attract many more motorists than used them before their improvement.', 'As a general rule, the greater the number of lanes on a given length of highway, the lower the rate of accidents per 100, 000 vehicles traveling on it.']