To go by bicyckle; Follow road 715 towards Trondheim (separate cycle path on parts of the road from Trolla to Ilsvika) –> Fv 715 / Ilevollen → around the construction zone at Ila/Ilen church → Erling Skakkes gate → into the city centre. You can also use Sandgata as the alternative corridor to/from the centre.
Cars must use alternatives via Rv 706 Nordre Avlastningsveg: Fv 715 from the west → take Rv 706 / Nordre Avlastningsveg → enter the centre from the north/east side → towards Kjøpmannsgata → city centre.
See moore information here (in Norwegian)