Uber has been taking passengers from taxis, one by one, on the busiest streets of Manhattan, as we wrote in October. But is that shift in the city’s transportation habits consistent all day long, or are there peak periods when the new ride-for-hire service is adding more trips to the streets than taxis are losing? In other words, is Uber making congestion worse at some hours of the day?

That was the question asked by one of our readers, Kimberly Ziev Niehaus, in a comment she left on our October article.

It’s a good question because our previous analysis treated all rides the same, no matter what time of day they started. But congestion is a function of how many cars are on the road at the same time — not of how many there are at other times of day. We looked more closely at the data we used in our earlier analysis, when we compared taxi and Uber pickups from April, May and June of this year with pickups in the same months a year earlier. We found that there were some subtle but meaningful differences in Uber and taxi usage by hour during a typical weekday.

In the morning, Uber did not add extra trips to the streets in the area known as the Manhattan core — south of 110th Street on the West Side and 96th Street on the East Side. Uber added fewer rides than taxis lost during those hours, resulting in a net decrease in the number of trips by taxis and Ubers. But that picture changed in the evening rush hour, beginning at 4 p.m. During those hours, Uber added more trips than taxis lost. The total number of pickups for both services rose during the evening rush from 4 to 7 p.m. and again from 9 p.m. to 1 a.m.

These increases weren’t enormous: The biggest change during busy hours was a 4 percent rise in pickups between 4 p.m. and 5 p.m. — or an average of 682 additional pickups per non-holiday weekday during that hour. For comparison, there are, on average, about 24,000 vehicles on all the roads in Manhattan’s central business district — the part of the island south of 59th Street, which is most of the core — at any time between 2 p.m. and 8 p.m. on weekdays, according to estimates made by transportation economist Charles Komanoff in his model of Manhattan traffic.

Uber maintains that any increase it is generating in overall traffic is minimal.

“As I was over the summer, I’m still skeptical this is having an impact on congestion in a material way,” Josh Mohrer, general manager of Uber in New York City, said in a telephone interview. He pointed out that our analysis doesn’t consider whether Uber is replacing rides in private cars or by other ride-for-hire companies. “Uber is taking lots of cars off the road and will continue to do that,” he said.

The increase in total Uber and taxi pickups during evening rush hours and later at night wasn’t spread evenly between the two competing services. Instead, Uber pickups surged by more during that time than they did the rest of the day, while taxi pickups experienced their biggest drops.

One possible explanation for why Uber did better than taxis beginning at 4 p.m.: The yellow-taxi shift change between 4 p.m. and 5 p.m. That’s when drivers go off duty as they return their cabs to garages for fresh drivers. Perhaps some of the people who waited a long time to hail cabs during and just after the shift change last year switched to Uber as it added drivers in New York. It’s less clear why Uber took so many taxi rides even hours after the shift change.

The picture is very different when you look outside the Manhattan core, in the other four New York City boroughs and northern Manhattan. In these areas, Uber added substantially to the number of for-hire vehicles on the street throughout the day.

Ubers increased pickups outside the Manhattan core, especially in the evening, presumably as more people heading home from nights out chose a car and driver over a bus or subway.

Read more:

Uber Is Taking Millions Of Manhattan Rides Away From Taxis

New York’s Green Cabs Stay Close To The City Center

Public Transit Should Be Uber’s New Best Friend

Uber Is Serving New York’s Outer Boroughs More Than Taxis Are