Weekday subway trains are more punctual than they have been in six years, officials announced Thursday — but warned the improvements will plateau without some high-tech upgrades.

The MTA announced 84% of weekday subway trains ran “on time” last month, up from 68.8% in August 2018 and the highest rate since September 2013.

The number of weekday delays also fell 52% in the past 12 months, to fewer than 29,000. The MTA defines a train as “on time” if it arrives within six minutes of its scheduled time.

Buses and subways chief Andy Byford credited the improvements to his “Save Safe Seconds” signal re-timing efforts — but said he wanted to get to on-time performance into the “high 90s” and that wouldn’t be possible without a “steep change in infrastructure.”

“What we have been doing is squeezing every possible ounce of performance improvement out of existing infrastructure and out of existing equipment, but we still have, in many cases, 100-year-old equipment,” Byford told reporters.

“It will be increasingly difficult to squeeze more out of the system given that we are hampered by hampered by the limitation of existing technologies.”

Despite the improving marks, straphangers still often deal with tardy trains on a day-to-day basis. Delays were reported on at least 12 lines Thursday morning.

Byford has asked for $40 million to fund his Fast Forward Plan — an ambitious proposal to modernize the subway by updating its antiquated signaling system, which is the biggest issue causing delays.

The embattled agency’s capital plan must be approved by the board by Oct. 1 and is expected to have a price-tag of upwards of $50 billion, but the list of projects it will fund remains under wraps.