systematica

THE LIFE AND DEATH OF URBAN HIGHWAYS

Cities need roads, and sometimes they even need highways, but few cities have thought systematically about when and where they need highways. Highways have a very specific role to play in an overall transportation system: to move traffic long distances at high speeds. While urban passenger trips can generally be moved most efficiently by some other means than private cars, buses and trucks need to use roads, and these trips are much harder to replace. Both long-distance trucks and buses are heavy-weight vehicles that tear up roads, have difficulty stopping suddenly, and have large engines that pollute heavily and make a lot of noise. Therefore, it is frequently desirable to get as many large trucks and long-distance buses as possible off of local streets. Urban highways should prioritize the rapid movement of suburban and inter-city bus and truck trips and could include exclusive lanes for buses to ensure high capacity passenger moment. However, such facilities are not as useful for short urban trips, because the indirectness of routes between a trip origin and destination undermines the time saved from the higher speed achieved by limiting access points. Highways were typically sought as a solution to congestion. Years of evidence has shown that highways in fact do not alleviate congestion. While expanding road capacity might provide relief for the first few years, it is likely to have the opposite effect, even within the first five years of operation (Duranton and Turner, 2011). By the late 1960s, traffic engineers from both the United States and the United Kingdom had observed that adding highway capacity was not decreasing travel times, and theorized that this was due to additional trips that were generated or induced because of the new roads. Since then, numerous empirical studies and analysis of real world case studies have shown that new road capacity usually induces traffic in direct proportion to the amount of new road space; removing roadways similarly reduces traffic (Cairns, Hass-Klau and Goodwin, 1998), with traffic growing by 0.4 to 1.0 as much as new capacity in the long-run (Hensher, 1977; Noland and Lem, 2000). READ THE FULL PDF: http://www.itdp.org/documents/LifeandDeathofUrbanHighways_031312.pdf