To put it into perspective for the British readers. Imagine the London orbital was lacking a bit, e.g. no M25 between Oxted and Merstham, and all the traffic would go through local roads.
The highway would bring extreme noise and pollution to the city.
On the contrary. Closing the ring Autobahn gap would very much reduce the traffic - especially the stop-and-go traffic on local roads. The new piece of Autobahn would be forced to be very low on noise, as Germany already has insane requirements on sound insulation for new and renovated roads - there was a news item recently that they had to erect a sound isolating barrier on a German road to protect a cemetry from the noise. As if the inhabitants would complain.