Federal regulations that would require hybrids and electric cars to emit pedestrian-warning noises have been delayed, yet again.
Because these cars operate near-silently on electric power, there has been concern among regulators that they constitute a greater safety risk to pedestrians than noisier internal-combustion cars.
That led Congress to pass a law in 2010 directing the National Highway Traffic Safety Administration (NHTSA) to issue regulations requiring these "quiet cars" to make more noise.
But these "quiet car" rules now won't be finalized until at least March, according to Reuters.
NHTSA Administrator Mark Rosekind said in July that the agency would finalize rules by November, but it apparently wasn't able to meet that target.
The deadline for these rules was originally set for January 31, 2014. An initial proposal was made in 2013.
2016 Toyota Prius Two Eco
That proposal called for vehicles to produce sounds above background noises, at speeds up to 18.6 mph.
These rules would apply to all hybrid and electric cars, along with other quiet vehicles that don't emit powertrain noises.
It's understood that carmakers would have some leeway in choosing sounds, although certain minimum requirements will be put in place.
Each vehicle of the same make and model would reportedly have to emit the same sound or sounds.
Regulators believe minimal noise levels are necessary to alert pedestrians--particularly those that are visually impaired--to the presence of a vehicle.
The NHTSA estimates that odds of a hybrid car being involved in a collision with a pedestrian are 19 percent higher than with an internal-combustion vehicle.
Ford Fusion Energi charging.
However, carmakers have argued that the proposed rules will make hybrids and electric cars too loud--louder than high-performance sports cars, even.
MORE: Laws To Add Noise To Silent Electric Cars: Latest Updates (Jan 2014)
Carmakers have 18 months from when the rules are finalized to add the noise-making devices.
The NHTSA said in 2013 that it expects the rules to cost carmakers $23 million in the first year.
Most of that cost was anticipated to come from adding external waterproof speakers to cars.