Table 3.

First-stage relationship between orientation to highway and frequency downwind.

Dependent variable:	Frequency downwind
	(1)	(2)
Highway northeast	0.005	−0.025
	(0.010)	(0.009)
Highway east	0.031	−0.025
	(0.016)	(0.024)
Highway southeast	0.071	0.053
	(0.014)	(0.012)
Highway south	0.109	0.109
	(0.013)	(0.013)
Highway southwest	0.221	0.194
	(0.026)	(0.024)
Highway west	0.242	0.187
	(0.036)	(0.034)
Highway northwest	0.029	0.024
	(0.028)	(0.022)
F-statistic	30.4	26.5
Partial R2	0.551	0.653
Highway segment FE		Yes
N	9027	9027

Notes: Each column represents a separate regression of the frequency downwind on seven indicators summarizing orientation to the nearest major highway. The omitted category is north. The observation is the census block, and the sample is limited to census blocks with centroids between 50 and 600 m from major highways. Parentheses contain standard errors clustered on a spatial grid with a width of 0.05 degrees longitude or latitude in each cell. All regressions include controls for distance to highway, weather station fixed effects, share African-American, and share over ages 50, 55, 60, 65, 70, and 75. Regressions without highway segment fixed effects include quintics in latitude and longitude and first- and second-order interactions between latitude and longitude. Regressions with highway segment fixed effects include highway segment fixed effects with an 800 m bandwidth. The F-statistic tests the hypothesis that all seven orientation indicators equal zero; the partial R² is the R² generated by these seven orientation indicators after partialing out controls.