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1、 www.vtpi.orgInfovtpi.org250-360-1560 Todd Litman 1998-2010 You are welcome and encouraged to copy, distribute, share and excerpt this document and its ideas, provided the author is given attribution. Please send your corrections, comments and suggestions for improvement. Generated Traffic and Induc
2、ed Travel Implications for Transport Planning 19 August 2010 Todd Litman Victoria Transport Policy Institute Abstract Traffic congestion tends to maintain equilibrium. Congestion reaches a point at which it constrains further growth in peak-period trips. If road capacity increases, the number of pea
3、k-period trips also increases until congestion again limits further traffic growth. The additional travel is called “generated traffic.” Generated traffic consists of diverted traffic (trips shifted in time, route and destination), and induced vehicle travel (shifts from other modes, longer trips an
4、d new vehicle trips). Research indicates that generated traffic often fills a significant portion of capacity added to congested urban road. Generated traffic has three implications for transport planning. First, it reduces the congestion reduction benefits of road capacity expansion. Second, it inc
5、reases many external costs. Third, it provides relatively small user benefits because it consists of vehicle travel that consumers are most willing to forego when their costs increase. It is important to account for these factors in analysis. This paper defines types of generated traffic, discusses
6、generated traffic impacts, recommends ways to incorporate generated traffic into evaluation, and describes alternatives to roadway capacity expansion. A version of this paper was published in the ITE Journal, Vol. 71, No. 4, Institute of Transportation Engineers (www.ite.org), April 2001, pp. 38-47.
7、 Generated Traffic: Implications for Transport Planning Victoria Transport Policy Institute 1Contents Introduction . 2 Defining Generated Traffic . 3 Measuring Generated Traffic . 6 Modeling Generated Traffic . 11 Land Use Impacts . 13 Costs of Induced Travel . 14 Calculating Consumer Benefits . 16
8、Example . 18 Counter Arguments . 22 Alternative Strategies for Improving Transport . 24 Legal Issues . 25 Conclusions . 26 Resources . 27 This illustration from Asphalt Bulletin magazine shows how expanding roadway capacity tends to stimulate automobile travel and the need for more roads. Generated
9、Traffic: Implications for Transport Planning Victoria Transport Policy Institute 2Introduction Traffic engineers often compare traffic to a fluid, assuming that a certain volume must flow through the road system. But urban traffic may be more comparable to a gas that expands to fill available space
10、(Jacobsen 1997). Road improvements that reduce travel costs attract trips from other routes, times and modes, and encourage longer and more frequent travel. This is called generated traffic, referring to additional vehicle traffic on a particular road. This consists in part of induced travel, which
11、refers to increased total vehicle miles travel (VMT) compared with what would otherwise occur (Hills 1996). Generated traffic reflects the economic “law of demand,” which states that consumption of a good increases as its price declines. Roadway improvements that alleviate congestion reduce the gene
12、ralized cost of driving (i.e., the price), which encourages more vehicle use. Put another way, most urban roads have latent travel demand, additional peak-period vehicle trips that will occur if congestion is relieved. In the short-run generated traffic represents a shift along the demand curve; reduced congestion makes driving cheaper per mile or kilometer in terms of travel time and vehicle operating costs. Over the long run induced travel represents an outward shift in the
