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8S E C T I O N 2 Transportation systems and land use patterns coexist in a complex and ever-evolving âeco- system.â Roads and transit systems are planned and constructed in order to serve existing homes and businesses, but new homes and businesses also locate where they will have access to existing or planned roads and transit systems. A host of other factors affect this ecosystem, including land values and availability, public policies, and public support for land development (often demonstrated through government intervention). 2.1 Evidence for the Land Use Effect and Land Use Benefits A growing body of research analyzes the extent to which public transportation systems beget land use changes in the form of more compact development. The evidence is mixed, but favors the theory that public transportation investments can, under the right circumstances, promote more compact development. The TCRP Project H-46 research team calls this phenomenon the land use effect of transit (or simply the land use effect). (See Figure 1.) There are numerous exam- ples of recently constructed or improved rail and bus lines in the United States and abroad that have attracted new homes, drawn new jobs, and increased property values (Center for Transit- Oriented Development [CTOD] 2011, Nelson et al. 2011, Huang 1996, Cervero et al. 1995). There are also examples from the literature of new transit nodes that have attracted little to no new prop- erty development, often because they are sited in locations with poor market demand, poor job access, or limited government support for development (CTOD 2011, Cervero et al. 1995, Kolko et al. 2011). Transit service supports densification in transit-adjacent areas, but it is not sufficient for densification in the absence of other factors. There is also some evidence that transit systems, in particular suburban commuter rail systems, encourage development to spread out from the urban core (Landis and Cervero 1999, Chatman and Noland 2013). This can result in a decrease in gross population densities as the region grows in size. Still, it is clear from the literature that transit systems support compact development in most cases. Compact development in turn provides a host of environmental and social benefits. The focus of this research is benefits in terms of travel patterns, energy use, and GHG emissions. We call these benefits the land use benefits. (See Figure 1.) Since land use effects lead to land use benefits, these terms are sometimes used interchangeably. An extensive literature demonstrates that people living in compact developments, even people who do not use transit, tend to drive less and walk and bike more. In Growing Cooler, the authors find that for every 1% increase in density, VMT is reduced by 0.3%. In other words, the elasticity of VMT with respect to density is -0.3 (Ewing et al. 2008). This lower rate of driving saves fuel and thereby reduces GHG emissions. (Vehicles driving in denser areas do burn slightly more Transitâs Impact on GHG Emissions and Energy Use: The Land Use Component
Transitâs Impact on GHG Emissions and Energy Use: The Land Use Component 9 fuel per mile due to lower speeds and roadway congestion, but this congestion effect is dwarfed by the effect of lower VMT.) Some studies refer to the land use effect and land use benefits of transit as the indirect effect of transit. 2.2 The Ridership Effect The land use effect of transit is complementary to, but completely separate from, the ridership effect of transit on VMT, fuel use, and GHG emissions. (Some studies refer to this as the direct effect of transit.) Many people riding buses and trains would travel in private vehicles instead if transit were not available. A typical estimate is that one out of every two or three transit patrons would drive a car if transit were not available (APTA 2009). Others would carpool, use another form of transportation, or not make the trip. Reducing VMT through transit ridership in turn reduces fuel consumption and GHG emissions. Transit also reduces fuel use and GHG emissions by reducing on-road congestion (APTA 2009). 2.3 Other Benefits Besides the effects of compact development on travel patterns, there are numerous other benefits of compact development. Buildings in compact developments tend to use less energy for heating and cooling and less water for landscaping (Ewing and Rong 2008). Saving energy Figure 1. Land use effects and land use benefits of transit.
10 Quantifying Transitâs Impact on GHG Emissions and Energy UseâThe Land Use Component and water and driving less in turn produce cost savings for residents of compact areas. Compact developments are also able to make more efficient use of infrastructure, requiring fewer miles of roads, electric lines, and water and sewer lines per person than sprawling developments (Morris Beacon 2010, City of Champaign 2010, Maryland Department of Planning 2010, Smart Growth America 2013). Service costs such as police and fire are also lower per person when concentrated in a smaller area (City of Champaign 2010). Service and infrastructure cost savings mean less public spending. There are also social and health benefits to living in compact developments, as residents can have better access to services and amenities and more opportunities for physical activity in the form of walking and biking (Design, Community & Environment et al. 2006). These additional benefits of compact development are not directly treated in this research. 2.4 Focus of This Research This research analyzes and explains the land use effect of transit and the land use benefits in terms of reduced VMT, fuel use, and GHG emissions. The research both tests the theory that transit investments can foster more compact development and quantifies the strength of the relationship. The bulk of the research effort was devoted to analyzing the connection between transit investments and land use patterns: the land use effect (Figure 1). This link in the causal chain is the least understood and the most highly disputed. It therefore received the most attention. The second link in the causal chain is better understood. The relationship between land use patterns and VMT is one of the most frequently studied topics in the planning literature in recent years, with more than 200 studies published (Ewing and Cervero 2010). There is broad consensus on the magnitude of the relationship; however, this relationship is analyzed again herein.
