Transit leaders say the subway is getting better as they work to overhaul the system, but riders are more likely to have felt the improvements on some lines than on others.

Passengers of the E line saw their rides get faster by one minute and 14 seconds on average in May, compared with the same month last year. Riders of the L, J, Z and W lines, however, saw their average ride get a few seconds slower.

That’s all according to a Metropolitan Transportation Authority metric called “additional train time,” which tracks how well train lines perform against the agency’s estimates for how long each ride should take. For example, if the M.T.A. says you should be able to go from Court Square to the Hudson Yards station on the 7 line in 15 minutes, additional train time measures any time you spend onboard the train beyond those 15 minutes. (A separate statistic measures how long you spend waiting on the platform.)

Ideally, all lines would have an additional train time as close as possible to zero — in other words, they would run on schedule. No line in the subway has achieved that goal yet, but some of them are close. And most lines got better compared with the same month last year.

The E line saw the most improvement. In May, the average additional train time was 23 seconds — not zero, but far better than the one minute and 37 seconds that the E was running behind in May of last year.

Below are the lines with the largest reduction in additional train time, ranked by how much time they saved per trip, on average.

Changes in duration of train ride by subway line The goal is to get trains running as close as possible to zero. AvERAGE time spent beyond RIDE estimate 1 min 2 min 0 min 1:14 E May 2019 May 2018 Average time in minutes and seconds saved per ride in the last year. 0:57 F 0:49 7 0:46 A 0:44 Q 0:41 5 The goal is to get trains running as close as possible to zero. AvERAGE time spent beyond RIDE estimate 0 min 1 min 2 min 1:14 E May 2019 May 2018 Average time in minutes and seconds saved per ride in the last year. 0:57 F 0:49 7 0:46 A 0:44 Q 0:41 5

The next group of lines shaved 13 to 34 seconds on average per trip.

1 min 2 min 0 min 0:34 D May 2019 May 2018 0:29 C Average time saved per ride in the last year. 0:29 2 0:26 4 0:23 M 0:22 3 0:20 G 0:15 N 0:13 B 1 min 2 min 0 0:34 D May 2019 May 2018 0:29 C Average time saved per ride in the last year. 0:29 2 0:26 4 0:23 M 0:22 3 0:20 G 0:15 N 0:13 B

Shaving off a few seconds — or even a minute — may not seem like a very perceptible change to your commute, but the average reflects fewer delays and major incidents that, over the course of a month, make a noticeable impact on the subway experience. Over all, it means commutes on these lines have become more reliable.

The rest of the lines saw little improvement or got worse.

1 min 2 min 0 min Average time saved per ride in the last year. 0:13 1 May 2019 May 2018 0:11 6 0:06 R 0:01 S 42nd St. + 0:01 Additional train time for these lines increased. L + 0:03 J Z + 0:04 S Franklin Ave. + 0:06 W + 0:21 S Rockaway 1 min 2 min 0 min Average time saved per ride in the last year. 0:13 1 May 2019 May 2018 0:11 6 0:06 R 0:01 S 42nd St. + 0:01 Additional train time for these lines increased. L + 0:03 J Z + 0:04 S Franklin Ave. + 0:06 W + 0:21 S Rockaway

Some lines already had a good track record for running on time and could not get much better. The L line, for example, has a modern signaling system and was among the subway’s top on-time performers.

The J and the Z lines, which already performed poorly relative to other lines a year ago, got a little slower.

Transit advocates favor the “additional train time” metric over the more widely used “on-time performance” statistic, which measures the percentage of trains that reach the final station within five minutes of the schedule — about 80 percent now, compared with 65 percent in 2017.

Mary Buchanan and Tabitha Decker of the TransitCenter, an advocacy group, said the new metric better reflects riders’ experiences. But they said that data on the lettered lines is less accurate than data on the numbered lines because lettered lines do not have a precise train-tracking system.

The subway reached a low point two years ago, when the number of delays skyrocketed and a train derailed in Harlem. Subway officials spent hundreds of millions of dollars on repairs, and sped up trains by raising speed limits and fixing faulty signals.

The M.T.A. attributes the system’s overall performance improvement to these factors and to changes in schedule, which the agency said allow trains to run more efficiently.

Here’s another look at the lines, ranked by their average performance in May rather than by improvement.

Additional train time in May 2019 Average time in minutes and seconds that customers spend onboard a train beyond the estimated travel time, per trip. 0:30 1:00 1:30 2:00 J Z WORST B N D Q A M G 0:30 1:00 1:30 2:00 6 W 1 R BETTER 4 F S Franklin Ave. C 0:30 1:00 1:30 2:00 7 2 5 3 S 42nd St. S Rockaway E L BEST Average time in minutes and seconds that customers spend onboard a train beyond the estimated travel time, per trip. 0:30 1:00 1:30 2:00 J Z WORST B N D Q A M G 0:30 1:00 1:30 2:00 6 W 1 R BETTER 4 F S Franklin C 0:30 1:00 1:30 2:00 7 2 5 3 S 42nd S Rockaway E L BEST