  This paper uses a before-after, experimental-control group method to evaluate
the impacts of the newly opened Expo light rail transit line in Los Angeles on
personal vehicle greenhouse gas (GHG) emissions. We applied the California Air
Resources Board's EMFAC 2011 emission model to estimate the amount of daily
average CO2 emissions from personal vehicle travel for 160 households across
two waves, before and after the light rail opened. The 160 households were part
of an experimental-ccontrol group research design. Approximately half of the
households live within a half-mile of new Expo light rail stations (the
experimental group) and the balance of the sampled households live beyond a
half-mile from Expo light rail stations (the control group). Households tracked
odometer mileage for all household vehicles for seven days in two sample waves,
before the Expo Line opened (fall, 2011) and after the Expo Line opened (fall,
2012). Our analysis indicates that opening the Expo Line had a statistically
significant impact on average daily CO2 emissions from motor vehicles. We found
that the CO2 emission of households who reside within a half-mile of an Expo
Line station was 27.17 percent smaller than those living more than a half-mile
from a station after the opening of the light rail, while no significant
difference exists before the opening. A difference-in-difference model suggests
that the opening of the Expo Line is associated with 3,145 g less of household
vehicle CO2 emissions per day as a treatment effect. A sensitivity analysis
indicates that the emission reduction effect is also present when the
experimental group of households is redefined to be those living within a
kilometer from the new light rail stations.
