NEW YORK, Jan. 4 (Xinhua) -- New York's Metropolitan Transportation Authority (MTA), the largest transit operator in the United States, has been attempting to keep riders safe amid the COVID-19 pandemic by applying new technologies, The Wall Street Journal reported Sunday.

However, "some solutions are proving challenging as the science surrounding the virus shifts," the report said.

"We are trying to figure this out as we go," Mark Dowd, the MTA's chief innovation officer, was quoted as saying.

For example, it has been unclear whether using electrical fields in mass-transit vehicles to kill viruses and bacteria is effective and safe, the report said.

It is "an emerging technology that can create a byproduct that carries a potential, if small, risk to human health," the report quoted Brian Buckley, executive director of laboratories at Rutgers Environmental and Occupational Health Sciences Institute, as saying.

So far, MTA officials have not found any such byproduct created in the testing vehicles, the report said, but adding that Buckley suggested "more study of the technology is needed."

The MTA had previously spent 1.3 million U.S. dollars attempting to apply ultraviolet light to subway cars and buses, but later abandoned the solution as it proved unpractical to vacate the vehicles, install the equipment and apply the technology "on a fleet numbering in the thousands," it said.

The MTA had also spent 775,000 dollars attempting to use antimicrobial sprays to sanitize surfaces, most of which proved ineffective, it added.

As of Sunday afternoon, New York City had registered 439,921 confirmed COVID-19 cases, with 25,244 deaths, according to tracking project The City.

The MTA carries over 11 million passengers system-wide on an average weekday, and over 850,000 vehicles on its seven toll bridges and two tunnels per weekday.