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 model that calculates benefits from toll plans like Move NY, but can also assess the impact of almost any traffic-related change in NYC, especially Manhattan.

The finding about Uber’s traffic impact runs counter to the Daily News’ bald assertion in an editorial last Sunday: “From a traffic perspective, a few thousand new cars in Midtown and downtown (where 72 percent of the app cars make pickups) is a tablespoon in a lake.” 

The News would be right if we were only talking about another two or three thousand private autos joining the three-quarters of a million motor vehicles that are driven daily to or through Manhattan’s Central Business District, which would worsen CBD traffic speeds by a minuscule 0.2 percent, according to the BTA. But as the News itself pointed out, Uber now commands some 19,500 cars in the city, a figure that is growing by up to 2,000 a month. Compounding this, each Uber vehicle racks up five to six times as many CBD miles as one private car.

Even allowing that a third of Uber cars are inactive on a typical day, according to the News, that still means the remaining two-thirds are traveling approximately 190,000 miles daily in Manhattan south of 60th Street. (This assumes the average Uber trip consists of two miles with the passenger and half a mile without.) These miles are enough to add 5.7 percent to the 3,385,000 daily CBD “baseline” miles covered by cars, cabs, trucks and buses.

It would take an awful lot of private cars to gum up CBD traffic to the same extent. Indeed, based on my estimate that a typical auto driven into the Manhattan core covers about 2.7 miles before leaving the area, the extra number required would be 72,000 a day. When that number of additional daily cars is run through the BTA, the result is a projected 6.7 percent slowing of vehicular travel averaged across the entire Central Business District.

That 6.7 percent is an upper limit, since at least some of those Ubers are displacing yellow cabs, black cars (corporate liveries), or even private cars, and, thus, not adding to traffic. To what extent, no one knows yet, including DOT, which is embarking on a new CBD traffic study while it puts a hold on new for-hire vehicles (FHVs). But even if just half of Uber rides are additional rather than replacement auto trips, the impact is still noteworthy: 3-4 percent slower travel for everyone in a motor vehicle… and rising.

These aggregate figures are pretty abstract, so let’s bring them down to the level of the average trip. Another nugget from the BTA is that each mile driven by one automobile in the CBD slows down all other vehicles by a combined 10 minutes. (Note that the lost time varies enormously depending on the time of day, from less than half a minute in the middle of the night to as much as 18 minutes between 2 p.m. and 8 p.m.).

Taking into account the value of time, those 10 lost minutes equate to an estimated $7.25 worth of wasted time imposed on truckers, drivers, and passengers (to say nothing of pedestrians and cyclists, whose lost time and added stress from the extra traffic aren’t counted here). Thus, an Uber trip entailing 2.5 miles driven, as estimated above, is imposing an $18 “social delay cost” that easily exceeds the amount paid by the rider.

This vast gulf between Uber’s customer cost and its social cost makes a mockery of the contention that expansion of app-based FHVs is a win-win for everyone but medallion owners and yellow-cab drivers. In reality, adding vehicles to the CBD and much of NYC re-enacts the classic “tragedy of the commons” in which each participant is practically coerced into biting off another chunk of a finite resource until the whole is largely eaten away, leaving everyone with little or nothing.

The antidote to creeping Uber? Capture at least some of the damage from chipping away at CBD street space, by putting a price on it.

This means enacting congestion charges that compel drivers to anticipate the costs their car trip is about to impose. That’s what the Move NY plan does, via a “cordon fee” on cars and trucks entering and leaving the CBD, coupled with a “taxi surcharge” on yellow and green cabs and app-based FHVs (in lieu of the cordon fee).

By my estimates, this plan will put a price on more than 90 percent of all miles driven in Manhattan south of 60th Street. The benefits of reduced traffic and fully-funded transportation infrastructure will ripple across the city and the region.