Public transportation systems are often part of strategies to reduce urban environmental impacts from passenger transportation, yet comprehensive energy and environmental life-cycle measures, including upfront infrastructure effects and indirect and supply chain processes, are rarely considered. Using the new bus rapid transit and light rail lines in Los Angeles, near-term and long-term life-cycle impact assessments are developed, including consideration of reduced automobile travel. Energy consumption and emissions of greenhouse gases and criteria pollutants are assessed, as well the potential for smog and respiratory impacts.

Results show that life-cycle infrastructure, vehicle, and energy production components significantly increase the footprint of each mode (by 48–100% for energy and greenhouse gases, and up to 6200% for environmental impacts), and emerging technologies and renewable electricity standards will significantly reduce impacts. Life-cycle results are identified as either local (in Los Angeles) or remote, and show how the decision to build and operate a transit system in a city produces environmental impacts far outside of geopolitical boundaries. Ensuring shifts of between 20–30% of transit riders from automobiles will result in passenger transportation greenhouse gas reductions for the city, and the larger the shift, the quicker the payback, which should be considered for time-specific environmental goals.

Already the leading cause of weather-related deaths in the United States, extreme heat events (EHEs) are expected to occur with greater frequency, duration and intensity over the next century. However, not all populations are affected equally. Risk factors for heat mortality—including age, race, income level, and infrastructure characteristics—often vary by geospatial location. While traditional epidemiological studies sometimes account for social risk factors, they rarely account for intra-urban variability in meteorological characteristics, or for the interaction between social and meteorological risks.

This study aims to develop estimates of EHEs at an intra-urban scale for two major metropolitan areas in the Southwest: Maricopa County (Arizona) and Los Angeles County (California). EHEs are identified at a 1/8-degree (12 km) spatial resolution using an algorithm that detects prolonged periods of abnormally high temperatures. Downscaled temperature projections from three general circulation models (GCMs) are analyzed under three relative concentration pathway (RCP) scenarios. Over the next century, EHEs are found to increase by 340-1800% in Maricopa County, and by 150-840% in Los Angeles County. Frequency of future EHEs is primarily driven by greenhouse gas concentrations, with the greatest number of EHEs occurring under the RCP 8.5 scenario. Intra-urban variation in EHEs is also found to be significant. Within Maricopa County, “high risk” regions exhibit 4.5 times the number of EHE days compared to “low risk” regions; within Los Angeles County, this ratio is 15 to 1.

The project website can be accessed here.