The longest through route in Thunder Bay is ArthurSimpsonFortWilliamWaterCumberlandHodderCopenhagen StreetAvenueRoad, which starts at the western city limits, through the south end, then along the east side of the city between the city and the lake, up to the northern city limits. It continues for several miles heading north, and going west, it runs about a mile before it connects to the new highway. Except for Copenhagen Road, this
used to be Highway 11B/17B (and before that, was simply 11/17) but it was downloaded in 1998.
It's 27.4km. Include the parts outside of city limits, and it's
37.4km.
The second longest is the Thunder Bay Expressway/Highway 61, which starts at the eastern city limit and goes to the western city limit, and skirts along the western edge of the city.
It's 26.6km, but if you ignore the portion that is in Shuniah and connect the two pieces that are in Thunder Bay, it's
29.3km.