4.3.4 Global Climate Change
The Intergovernmental Panel on Climate Change (IPCC) defines climate change as the “state of any change in climate over time, whether due to natural variability or as a result of human activity [11].” Trapped heat in the atmosphere is a major driver of global climate change. Gases that trap heat in the atmosphere are called greenhouse gases [12]. Motor vehicle fuel production and consumption release greenhouse gases, mainly CO2, a major contributor to global climate change. EPA estimates that CO2 represents about 30 percent of all greenhouse gas emissions. There are mitigation and damage costs associated with global climate change. Damage costs are costs related to the environment, health, and reduced economic productivity.
TRIMMS employs the damage costs, or the cost of a change in greenhouse gas emissions associated with motor vehicle use. The unit of measure is the marginal damage in U.S. dollars caused by a metric ton of CO2 emissions ($/tC). Since cost estimates vary widely across the literature, the estimate of $50/tC by Tol [33] who analyzed and combined 103 estimates of marginal damage costs of carbon dioxide emissions from 28 published studies was adopted. The mean marginal damage cost that takes into account of only peer‐reviewed literature (pp.2070) is used and scales to dollar per kilogram ($/kg).
Note that while TRIMMS only considers the marginal damage costs associated with CO2 emissions, other authors provide more comprehensive estimates of greenhouse emission costs. For example, Delucchi [14] considers the global emission costs of pollutants other than CO2 by calculating a ratio of CO2 equivalent emissions to CO2 emissions. Since EPA [12, 13, 34] considers these other greenhouse gases as more volatile and difficult to estimate, the EPA approach that only models CO2 global emissions is followed.
4.3.5 Noise Pollution
Noise costs refer to negative externalities associated with motor vehicle noise emissions. Motor vehicles produce noise from engine acceleration and vibration, from tire contact on road surfaces, from brake and horn usage. Noise disrupts sleep, activities, causes stress, and negatively affects property values. Several studies monetize traffic noise costs (see for example, Delucchi [35]). Noise cost estimates by Tod Litman [36], who comprehensively reviews the literature and provides estimates by mode type for urban and rural areas, were used. These estimates are reproduced in Table 2. In TRIMMS, these costs are scaled to account for cost of living differentials between national averages and each regional area.
4.4 Elasticity Parameters
TRIMMS estimates changes in trips using trip demand functions that rely on constant elasticity of substitution (CES) parameters that are explained in more detail in Appendix A.1. Elasticities measure user’ responsiveness to changes in pricing and travel times. Elasticities are used to measure the percentage change in demand of a good caused by a one‐percent change in its price or other characteristics. For example, an elasticity of ‐0.5 for single occupancy vehicle trips with respect to fuel costs means that each 1 percent increase in the price of fuel results in a 0.5 percent reduction in the demand for vehicle trips.
TRIMMS trip demand functions make use of direct elasticities and cross elasticities. Direct elasticities refer to the percentage change in the demand for trips of any given mode resulting from a change in its own price or other measurable characteristics. Cross elasticities refer to the percentage change in the demand for trips of any given mode caused by a change in price or other measurable characteristics of other modes. For example, an increase in parking prices causes a direct negative percent change in the demand for auto trips and causes a positive change in the demand for transit services. The use of cross elasticities recognizes a certain degree of substitution, or mode shift, between transport modes; the intensity of substitution depends on circumstances and is measured by the cross elasticities.
To obtain default parameters, the empirical literature was surveyed. There are a number of excellent surveys of the empirical literature on the demand for transportation and the role of elasticities [37‐40]. TRIMMS uses parameters from these studies and other publications.
TRIMMS default elasticity parameters can be accessed by clicking on the elasticity button on the toolbar (Figure 19).