How to reduce/get rid of background sounds like traffic noise

Traffic/street noise is extremely difficult to reduce and impossible to remove as it has components in every part of the spectrum, all of which are constantly changing. A 'noise print' reduction method won't work, neither will a graphic EQ. As cc_merchant says you're basically stuck with using it as-is or reshooting. You might be able to cut out the very low frequency rumbles with a high-pass filter if your vox is clear of that range (female speaker or child), but anything you do that would reduce the noise appreciably would turn your interviewee into a Dalek.

For interviews, sound engineers usually work to a -12dB peak as it gives enough headroom for any unexpected loud noises (coughs, clapping, etc.) while maintaining a good S/N ratio in the recording device preamps. Provided the ambient is low enough (unfortunately not in your case!) you can normalize and compress a -12dB track to broadcast levels using the volume and compressor effects in Premiere without needing to do any noise reduction.

You might want to post a sample of the audio over on the Audition forums: Audition CS5.5, CS6 & CC.  Many of the users there can help you.

Reshoot.