Metrobuses and trains are experiencing fewer delays caused by mechanical issues, but the transit agency continues to struggle with on-time performance.

Between 2015 and 2016, the reliability of Metro’s trains improved by about 13 percent, according to a “Vital Signs” performance report released by the transit agency on Monday.

That means that, on average, each of Metro’s rail cars traveled 65,029 miles, or about 11.5 months, before it experienced a failure that caused a delay of four minutes or more — just barely surpassing the agency’s target of an average 65,000 miles between delays.

That’s a significant coup for Metro, considering that the agency estimates that about 65 percent of delays on the rails are caused by problems with the cars. General Manager Paul J. Wiedefeld has made railcar reliability a major priority for 2017, launching a “Back2Good” repair campaign.

But even with last year’s improvements, railcar reliability was still 1.4 percent below the fleet’s performance two years ago, in 2014. And reliability differed greatly between types of cars, with the decade-old 6000-series leading in performance with an average 103,121 miles between delays, trailed by the brand-new 7000-series cars, with an average 82,611 miles between delays. (Metro says they expect the reliability of the 7000-series to improve with time as they diagnose and tweak problems with the new cars.)

Metro’s worst-performing cars — the soon-to-be-retired 4000-series — amassed a paltry 27,259 miles between mechanical failures that caused significant delays.

For Metrobuses, mechanical performance improved by an even larger margin: the reliability of the bus fleet increased by nearly 16 percent between 2015 and 2016. Metro exceeded its bus reliability goal by about 3 percent, with an average of 8,225 miles logged between breakdowns.

What caused the dramatic improvement? In the report, Metro officials said they have been retiring older and less-reliable buses, conducting 100 mid-life overhauls annually, and becoming more proactive about replacing and retrofitting defective parts.

“Nearly all fleet types experienced improved reliability, most notably the fleets that provide the most service, due to a number of mitigating and proactive actions implemented by bus maintenance,” Metro said in the report.

Still, there’s a problem: Though Metrobuses are operating more reliably than they have in several years, on-time performance continues to suffer. From 2015 to 2016, Metro’s adherence to the published bus schedule worsened by 2 percent, and bus punctuality fell 3 percentage points below target.

So, what’s the deal? If buses are running better than before, why are they still late? Metro offered a couple of explanations: Punctuality suffered during snow days in early 2016. And SafeTrack surges caused more people to flee the rails and opt for their cars, clogging up the roads and slowing down the progress of buses.

On-time performance for railcars was also pretty lackluster during the latter part of 2016: 80 percent of trains arrived on time last year, down from 84 percent in 2015 and 91 percent in 2014. In the report, staff acknowledged that rail performance suffered because of SafeTrack, and because of the increased reliance on speed restrictions resulting from more aggressive inspection protocol.

But as SafeTrack winds to a close, and Metro continues to make railcar mechanical improvements through the “Back2Good” project, officials are hoping that their investment in repairs and retrofits will finally translate into improved on-time performance in 2017.