The research, due to be published tomorrow, will show that at low speeds of 7-8 kmh (5mph) electric cars were just one decibel quieter than petrol cars. When speeds were increased to more than 20 kmh (12mph), the noise levels were "similar", with tyre noise dominating. "There does not appear to be any significant difference in the acoustic nature of [internal combustion engine] vehicles and [electric and hybrid] vehicles, and as such nothing suggests a pedestrian would clearly be able to differentiate between vehicle types," the report says.