Last week, the administration of Mayor Bill de Blasio unveiled its first express bus line: the 86th Street crosstown, running back and forth between York Avenue on the east side and Broadway on the west. There was a news conference to celebrate, at Columbus Avenue. Polly Trottenberg, the mayor’s transportation commissioner, hailed “modest investments” yielding dividends in terms of saved time for long-beleaguered riders, to which Ben Kallos, a city councilman, added that time saved translates into revenue for businesses whose taxes help pay for further transit improvements: a virtuous circle.