The transportation sector is a major source of air pollution worldwide, yet little is known about the effects of transportation infrastructure on air quality. In this paper we measure the effects of one major type of transportation infrastructure -urban rail transit -on air quality. Our approach uses the sharp discontinuity in transit utilization on the opening day of a completely new rail transit system in Taipei, Taiwan to identify the air quality effects of rail transit infrastructure.Using hourly air quality data from Taiwan we have three central findings. First, we find that the opening of the Metro reduced air pollution from one key tailpipe pollutant, carbon monoxide, by 5 to 15 percent. Second, we find little evidence that the opening of the Metro affected ground level ozone pollution. Third, we find little evidence suggesting that automobile travelers adjusted their time or route of travel to the availability of rail transit. These findings shed new light on the determinants of air quality, and suggest that environmental impacts are important components of the social value of transportation infrastructure.

We estimate the local spillovers from research university activity in a sample of urban counties. We use the fact that universities tend to follow a rigid endowment spending policy based on the market value of their endowments to identify the causal effect of university activity on labor income in the non-education sector. Our instrument for university expenditures is based on the interaction between each university's lagged endowment level and the variation in stock market shocks over time. We find statistically significant spillover effects from university activity, and the magnitude of the spillover is significantly larger when local universities are more research intensive or when firms are technologically closer to universities, as measured by labor market pooling and patent citations. The findings provide a rationale for place-based university policies, so long as they focus on industry fundamentals. The results also suggest that the longer-term effects that universities have on their local economies may grow over time as the composition of local industries evolve to take advantage of the knowledge spillovers we identify.

The spatial concentration of ideas is central to economic geography. Yet, how proximity to research affects productivity is not well studied. We use the late 19 th century establishment of agricultural experiment stations in the United States to estimate the importance of proximity to research for productivity growth. Our analysis of county-level agricultural census data from 1870 to 2000 reveals three results. First, research proximity effects from permanent station opening grew for about 20 years and then subsequently declined until becoming largely absent today. Second, proximity to station-based innovations affected local farmers' productivity for 20 to 40 years after the discovery. Third, research proximity effects remain today where stations historically focused on basic research and where nearby farmers were producing with frontier technology. Persistence in research proximity effects depend not just on research infrastructure, but also persistence in idea production and the cumulative effects of learning.

Every year billions of dollars are spent on research grants to produce new knowledge in universities. However, as grants may also affect other research funding the effects of financial resources on knowledge production remains unclear. To uncover how financial resources affect knowledge production we study the effects of research spending itself. Utilizing the legal constraints on university spending from an endowment we develop an instrumental variables approach. Our approach instruments for university research spending with time-series variation in stock prices interacted with cross-sectional variation in initial endowment market values for research universities in the United States. Our analysis reveals that research spending has a substantial positive effect on the number of papers produced, but not their impact.We also demonstrate that research spending effects are quite similar at private and public universities.