How responsible is Uber for the 9 percent drop in Manhattan travel speeds that New York City transportation officials reported last month? The answer appears to be: quite a lot. If — and it’s a big if — the surge in use of Uber and other app-based car services is not offset by a decline in use of yellow cabs and private autos, then three-quarters of the speed reduction can be laid at the feet of Uber, Lyft, et al. That’s according to my “Balanced Transportation Analyzer” (BTA) traffic modelthat calculates benefits from toll plans like Move NY, but can also assess the impact of almost any traffic-related change in NYC, especially Manhattan.