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37 aggregate impacts of all transit in the United States, also The preferred method to calculate the leverage factor used TTI's figures for fuel savings without modification. for a specific region is to conduct an SEM study specific to that region, using a household travel survey specific to the region. NYMTA is currently conducting such a study to best COMPACT DEVELOPMENT quantify the unique relationship between transit and land use in the New York metropolitan region. This type of study Several methods have been used to quantify the impact of requires a significant effort. An alternative method, avoiding transit on GHG emissions through compact development, a unique SEM study, uses the default national multiplier of but none have yet been widely accepted. The most common 1.9 calculated by the ICF study. This figure should be viewed way to account for the effect of transit on compact develop- as a placeholder, because land use patterns and transit service ment is through the use of a leverage factor, also known as vary substantially from region to region. APTA is currently a land use multiplier. The leverage factor accounts for the developing more detailed guidelines on how to evaluate the indirect benefit that transit provides to those people who do impact of transit on emissions through compact develop- not travel on transit, but whose walking, biking, and driving ment. The guidelines will provide instruction in conducting trips are made shorter by the influence of transit on land use. a tailored regional study, including required resources and To account for this indirect benefit, a leverage factor is used statistical techniques (50 ). to scale up the emissions reduced by direct mode shift of trips to transit. Leverage factors can be applied to mode shift effects cal- culated for existing services or to mode shift effects projected Leverage factors can be estimated for specific urban for specific strategies, although transit agencies should take regions, for specific transit modes, and for individual transit care in interpreting the latter. By using a leverage factor, services. Estimating unique leverage factors is often a com- transit agencies take credit for land use patterns that have plex and data-intensive exercise. Therefore, many analyses co-evolved with transit over many decades. Any new transit use average leverage factors drawn from the literature. A strategies would likewise take decades to realize their full recent CALPIRG study used individual leverage factors for effects on land use. A leverage factor therefore should be light-rail and heavy-rail transit (factor of 2), commuter rail treated as a long-term benefit of any strategies to improve (factor of 0.4), and bus and other transit (factor of 0). In this or expand transit. For TOD strategies, which directly affect case, a leverage factor of 2 means that each passenger mile compact development patterns, the benefits of land use could traveled on light or heavy rail reduces automobile VMT by 2 be calculated more easily. solely through the indirect effect of transit on land use (16 ). To be conservative, CALPIRG's study assumed that only Some regional agencies have conducted advanced mod- rail transit had an effect on land use patterns. CALPIRG's eling of how GHG emissions from transportation would leverage factors were based on assumptions drawn from change under various scenarios for development of land two previous studies (11,52). Empirical studies have found, use and transportation systems. The exercise is known as in different urban areas and for different transit corridors, land usetransportation scenario planning. Types of sce- leverage factors between 1.4 and 9 (4). narios evaluated typically include compact development and expansion of transit. The Sacramento Council of Govern- Another recent study used structural equations model- ments conducted such a study in 2004, using a sophisticated ing (SEM), a sophisticated statistical technique, to quantify software package, to establish a preferred scenario of growth the impact of transit on GHG emissions through compact for the region. Compared with a base case scenario in 2050, development. That study found that, nationwide, the com- Sacramento's Preferred Blueprint Scenario substantially pact development impacts of transit reduce GHG emissions increases the percentage of new jobs and housing near tran- by 29.9 MMtCO2 per year, or as much as all emissions from sit, reduces the number of trips taken by car by 10%, and all transportation in the state of Colorado (8) (see Table 2). reduces per capita CO2 emissions by 14% (53). A 2005 study The leverage factor calculated by the study was 1.9 (10 ). reviewed the results of this exercise and similar exercises in other regions in the United States. The study found that APTA's methodology considers SEM to be the most median impact on VMT for alternative scenarios was a 2% robust means to calculate a leverage factor, because it iso- to 3% reduction below base case scenarios (54). lates only the effects of transit on development patterns. Leverage factors calculated through other means tend to Analyses of land usetransportation scenarios are sub- capture characteristics of land use that are correlated with stantially more complex than the calculations described in but not necessarily induced by transit. Transit infrastructure APTA's methodology. In addition, there is no existing meth- is sometimes integrated into preexisting compact develop- odology to isolate the benefits of transit from those of land ment areas. SEM does not credit transit with the effects of use planning within such a study. Nevertheless, such exer- preexisting land use patterns on travel habits. cises can provide robust analyses of the combined impacts