Electric cars are quiet, but they won’t be for long. To help keep pedestrians safe, the United States Department of Transportation recently mandated that, starting in 2020, all new hybrid and all-electric vehicles must emit a noise when traveling at under 19 miles per hour. In 2015, however, Ford wanted to know if it could partially exempt the law enforcement vehicles it makes, The Verge has learned.

In the text of the final rule issued by the National Highway Traffic Safety Administration (NHTSA) this past February, the government said it would respond to a comment that was submitted by Ford “regarding the legality of equipping certain vehicles used for security purposes with a means of turning off the required pedestrian alert sound.” In other words, Ford told the government it plans to comply with the rule, but wanted to know if it was possible to give law enforcement an “off switch.”

Ford’s comment is redacted, and was only mentioned in the text of the final rule by mistake

Ford has created specific safety features for its law enforcement vehicles in the past, and it outfits these cars and SUVs in special ways so that they’re better suited for the needs of police or security services around the country. The company declined to comment on specifics of how police and security forces could or would benefit from this feature, saying only that it will “meet the requirements of this rule.” Equipping new law enforcement cars with a way to switch off the mandatory noise would presumably allow the cars to remain quiet in situations where officers don’t want to give away their location, like when they try to approach or apprehend a suspect.

The NHTSA never actually answers Ford’s question about the legality of an off switch in the rule, though. In fact, the text that references Ford’s request was “inadvertently left in,” a representative for the NHTSA tells The Verge. Ford submitted its request after the public comment period ended (in October 2015), and the NHTSA says it ultimately decided that “addressing the late comment would delay issuing the notice.” That Ford’s request was mentioned at all was actually a mistake.

The nature and breadth of Ford’s inquiry about silent cop cars, including where the idea originated from, is unclear because the company requested that the full text be redacted because it contains “confidential and proprietary” information, according to a Ford spokesperson. That request is still pending, according to the NHTSA, so the full comment will remain redacted until the review is complete.

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While an off switch might benefit law enforcement in certain situations, the government believes the mandatory noise will help keep pedestrians safe. A study performed by the NHTSA in the run-up to the rulemaking discovered hybrid vehicles were involved in crashes with pedestrians 1.18 times more than cars with internal combustion engines. The agency estimates that artificial noise at low speeds could prevent 2,400 injuries every year. Ford’s hybrid Interceptor police SUV makes up more than half of the market alone, and the rise in SUV sales over the last few years was recently linked to an increase in pedestrian deaths.

The two biggest companies chasing Ford in this market are GM and Fiat Chrysler of America. FCA declined to comment on future plans for its special service vehicles. GM did not respond in time for publish.