Practice — Reading Comprehension

Passage (abridged): "Urban planners have long assumed that adding lanes to a congested highway reduces travel time by increasing capacity. Traffic data from several expansion projects complicates this assumption: within a few years of an expansion, congestion levels often return to their pre-expansion state, even though the road itself is objectively wider. The likely explanation is that additional capacity attracts additional drivers who would otherwise have avoided the route, taken public transit, or travelled at a different time. The road is not failing to work; it is succeeding at attracting exactly the volume of traffic its new capacity can support." The primary purpose of the passage is to