The impact of Uber and Lyft on vehicle ownership, fuel economy, and transit across U.S. cities.

We estimate the effects of transportation network companies (TNCs) Uber and Lyft on vehicle ownership, fleet average fuel economy, and transit use in U.S. urban areas using a set of difference-in-difference propensity score-weighted regression models that exploit staggered market entry across the U.S. from 2011 to 2017. We find evidence that TNC entry into urban areas causes an average 0.7% increase in vehicle registrations with significant heterogeneity in these effects across urban areas: TNC entry produces larger vehicle ownership increases in urban areas with higher initial ownership (car-dependent cities) and in urban areas with lower population growth (where TNC-induced vehicle adoption outpaces population growth). We also find no statistically significant average effect of TNC entry on fuel economy or transit use but find evidence of heterogeneity in these effects across urban areas, including larger transit ridership reductions after TNC entry in areas with higher income and more childless households.

The estimated effect of mass or footprint reduction in recent light-duty vehicles on U.S. societal fatality risk per vehicle mile traveled.

The National Highway Traffic Safety Administration (NHTSA) recently updated its 2003 and 2010 logistic regression analyses of the effect of a reduction in light-duty vehicle mass on US societal fatality risk per vehicle mile traveled (VMT; Kahane, 2012). Societal fatality risk includes the risk to both the occupants of the case vehicle as well as any crash partner or pedestrians. The current analysis is the most thorough investigation of this issue to date. This paper replicates the Kahane analysis and extends it by testing the sensitivity of his results to changes in the definition of risk, and the data and control variables used in the regression models. An assessment by Lawrence Berkeley National Laboratory (LBNL) indicates that the estimated effect of mass reduction on risk is smaller than in Kahane's previous studies, and is statistically non-significant for all but the lightest cars (Wenzel, 2012a). The estimated effects of a reduction in mass or footprint (i.e. wheelbase times track width) are small relative to other vehicle, driver, and crash variables used in the regression models. The recent historical correlation between mass and footprint is not so large to prohibit including both variables in the same regression model; excluding footprint from the model, i.e. allowing footprint to decrease with mass, increases the estimated detrimental effect of mass reduction on risk in cars and crossover utility vehicles (CUVs)/minivans, but has virtually no effect on light trucks. Analysis by footprint deciles indicates that risk does not consistently increase with reduced mass for vehicles of similar footprint. Finally, the estimated effects of mass and footprint reduction are sensitive to the measure of exposure used (fatalities per induced exposure crash, rather than per VMT), as well as other changes in the data or control variables used. It appears that the safety penalty from lower mass can be mitigated with careful vehicle design, and that manufacturers can reduce mass as a strategy to increase their vehicles' fuel economy and reduce greenhouse gas emissions without necessarily compromising societal safety.

The effect of recent trends in vehicle design on U.S. societal fatality risk per vehicle mile traveled, and their projected future relationship with vehicle mass.

The National Highway Traffic Safety Administration (NHTSA) recently updated its 2003 and 2010 logistic regression analyses of the effect of a reduction in light-duty vehicle mass on US fatality risk per vehicle mile traveled (VMT). The current NHTSA analysis is the most thorough investigation of this issue to date. LBNL's assessment of the analysis indicates that the estimated effect of mass reduction on risk is smaller than in the previous studies, and statistically non-significant for all but the lightest cars. The effects three recent trends in vehicle designs and technologies have on societal fatality risk per VMT are estimated, and whether these changes might affect the relationship between vehicle mass and fatality risk in the future. Side airbags are found to reduce fatality risk in cars, but not necessarily light trucks or CUVs/minivans, struck in the side by another light-duty vehicle; reducing the number of fatalities in cars struck in the side is predicted to reduce the estimated detrimental effect of footprint reduction, but increase the detrimental effect of mass reduction, in cars on societal fatality risk. Better alignment of light truck bumpers with those of other vehicles appears to result in a statistically significant reduction in risk imposed on car occupants; however, reducing this type of fatality will likely have little impact on the estimated effect of mass or footprint reduction on risk. Finally, shifting light truck drivers into safer, car-based vehicles, such as sedans, CUVs, and minivans, would result in larger reductions in societal fatalities than expected from even substantial reductions in the masses of light trucks. A strategy of shifting drivers from truck-based to car-based vehicles would reduce fuel use and greenhouse gas emissions, while improving societal safety.

Real-World Emissions from Conventional Passenger Cars.

It has long been recognized that vehicles emit more pollutants than allowed under the new car emission standards. Further tightening of the certification standards based on existing test procedures does not directly address the largest sources of emissions. This study attempts to quantify vehicle emissions by source, in order to prioritize future policymaking. Several new sets of data are used in conjunction with regulatory emission models to characterize the lifetime emissions from the average Model Year (MY)93 vehicle. Special attention is paid to two of the largest sources of real-world emissions: (1) high-power driving by cars with properly functioning emissions controls, and (2) cars with malfunctioning emissions controls. Emissions are projected to MY2000 and 2010, based on estimates of the effectiveness of recently adopted and proposed regulatory policies. These new policies are projected to reduce total emissions substantially.