Audacity can’t remove traffic noises. Effect > Noise Removal only works with quiet noises that don’t change. It can’t take out airplanes either. Their noise is always changing. Noise Removal is good for quiet microphone hum or a refrigerator fan. Sometimes computer fan.
It’s job is to get rid of sounds lower in loudness than a set value. It’s not going to work for you either because the announcer and the noise are too close together.