Of the many ways the New York City subway unravels on a near daily basis, it has one Achilles’ heel that remains an impediment to any significant turnaround — the balky signals that control the trains.

This has long been known to subway officials who developed a plan years ago to upgrade the system’s dilapidated signals over the next half-century. For riders, that timetable is no longer acceptable.

Now Gov. Andrew M. Cuomo and transit leaders are suddenly promoting a different solution: ultra-wideband radio, a technology they say could shorten the timeline to under a decade.

But there is one problem — no one knows if it can actually work.

No major transit system has adopted it and researchers are still studying whether ultra-wideband radio can be used effectively in tunnels. Transit experts question whether it is wise to focus on an emerging technology, rather than ramping up the signal modernization efforts currently underway.