WASHINGTON — The U.S. Transportation and Treasury departments raised strong objections to a plan proposed by the Federal Communications Commission to shift much of a key spectrum block set aside for auto safety to accommodate the burgeoning number of wireless devices.

Documents reviewed by Reuters show strong pushback against the plan. The Transportation Department said the FCC plan is “a particularly dangerous regulatory approach when public safety is at stake.”

FCC Chairman Ajit Pai said this week the commission will vote Nov. 18 to finalize a plan to divide the 5.9 GHz spectrum block reserved in 1999 for automakers to develop technology to allow vehicles to talk to each other and traffic infrastructure, but has so far gone largely unused.

Pai would shift 30 megahertz of the 75 megahertz reserved for Dedicated Short-Range Communications to enable a different automotive communications technology called Cellular Vehicle-to-Everything, or C-V2X, while shifting the other 45 megahertz to Wi-Fi use.

The Transportation Department, however, said DSRC is proven to be safe while C-V2X one has not been fully tested. It warned the new technology might be susceptible to interference from nearby Wi-Fi devices, which could cause accidents.

Transportation Secretary Elaine Chao previously warned the FCC decision could result in “thousands more deaths annually on road and millions more injuries.”

Chao said in an Oct. 15 letter the FCC’s cost-benefit analysis is “fatally flawed” and puts efforts to use connected vehicle technology “in peril.”

Automakers oppose the split on safety grounds, while major cable, telecom and content companies say the spectrum is essential to support growing Wi-Fi use.

The FCC voted 5-0 to grant initial approval to the plan in December.

An Oct. 19 Treasury letter said shifting spectrum would be “insignificant to the “Wi-Fi industry in the long run, but puts the United States at a distinct disadvantage, especially vis-à-vis China, from market, innovation, and security perspectives.”

Treasury added “by reducing the transportation spectrum to 30 MHz, the United States would forfeit its lead in vehicle connectivity and smart infrastructure to China” and said C-V2X have “vulnerabilities that could be exploited by the Chinese.”

An FCC spokesman rejected the claims, saying C-V2X is less prone to interference “and far more likely to save lives than the long-stalled DSRC standard.”

The agency added “If we want to lead the world in automotive communications safety technology, the answer isn’t to double-down on the failed DSRC standard. That would be akin to doubling down on zeppelins with the aim of leading the world in air travel.”

In an Oct. 8 letter, Transportation Department general counsel Steven Bradbury said “additional Wi-Fi access should not come at the expense of transportation and public safety.”

He warned that while C-V2X “shows promise, it is still not fully test-proven.”

DSRC was previously offered on just one General Motors vehicle. Government studies have suggested the technology, if widely adopted among U.S. vehicles, could prevent at least 600,000 crashes annually.

“The FCC continues to move towards jeopardizing roadway safety,” GM said.