Number of subway passengers from Powell Station = retail revenues?

The Wall Street Journal reports that economists are looking to "oddball data" to see trends before official numbers are released.We're obviously a little obsessed with data reuse -- the more imaginative, the better. There's Ted Egan, the chief economist in the San Francisco Comptroller's office, who looks at weekend passenger tallies for the Union Square shopping district rather than wait six months for the state's official retail revenue numbers.  Then there's Edward Learner, the economist who discovered diesel fuel sales on Interstate Highway 5 is a leading indicator of construction employment in California, while diesel sales on Interstate Highway 80 is an indicator of manufacturing employment.The people who collected this data surely didn't imagine it being used this way, which is why we should be really careful about closing off data reuse before we even know what the potential reuses are.  And, as these economists have found, these indicators are often faster and arguably, more accurate.(P.S.  I used to live in San Francisco.  I know the Powell St. trolley is not the same as the Powell BART station.  Sorry.)