Quantifying Transit’s Impact on GHG Emissions and Energy Use—The Land Use Component (2015) / Chapter Skim
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Pages 56-66
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56 A P P E N D I X A This appendix contains a technical summary of the statistical models used, including datasets, model forms, and specifications of the best-fit models developed. It will give the reader an in-depth understanding of the elasticities developed for application in the TCRP Project H-46 research.
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Key Results from Statistical Models 57 • Urban design -- Urban design is not considered in the urban area model. In the neighborhood model, urban design is represented by the density of street intersections in the local area.
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58 Quantifying Transit's Impact on GHG Emissions and Energy Use -- The Land Use Component The primary purpose of the urbanized area model is to examine differences in travel behavior between urbanized regions that have experienced different levels and types of transit investment. The urbanized area models enabled the research team to answer the following research questions: • What is the total land use effect of an urban area's existing transit system?
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Key Results from Statistical Models 59 2000 and 2010. Variables tested but not ultimately included were average transit fares and vehicle revenue miles, both derived from the National Transit Database.
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60 Quantifying Transit's Impact on GHG Emissions and Energy Use -- The Land Use Component Results Table 6 includes elasticity values for the key variable relationships making up the land use effect and the ridership effect. An elasticity represents the percentage change in one variable associated with a percentage change in another variable in the model.
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Key Results from Statistical Models 61 another, where neighborhoods are distinguished primarily by their level of access to transit. This modeling exercise required collecting highly detailed data on neighborhoods and households within a handful of cities.
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62 Quantifying Transit's Impact on GHG Emissions and Energy Use -- The Land Use Component travel patterns and includes both population and employment densities. The neighborhood model also explicitly considers more land use characteristics: land use mixing, pedestrian environment, and job accessibility.
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Key Results from Statistical Models 63 Category Symbol Definition Level Primary outcome variable vmt Household daily VMT Household Intermediate outcome variables ttrips Household daily transit trips Household actden Activity density within 1/2 mile (sum of population and employment divided by gross land area in square miles) Household Exogenous transit variables emp30t Proportion of regional employment accessible within 30-minute travel time via transit (in-vehicle time only)
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64 Quantifying Transit's Impact on GHG Emissions and Energy Use -- The Land Use Component density is associated with a 0.11% decrease in VMT. This value is somewhat higher than typical values from the literature, but lower than the elasticity of VMT with respect to population density found in the urbanized area model.
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Key Results from Statistical Models 65 The best-fit neighborhood model finds two key transit variables that impact the land use effect: rail access and employment accessibility via transit. Both are intuitive components of the land use effect.
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66 Quantifying Transit's Impact on GHG Emissions and Energy Use -- The Land Use Component according to key transportation factors using a snapshot in time. The model is agnostic on the subject of the time it takes for development patterns to change in response to transit networks.
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