Photo of traffic back-up via our sister station, NBC15 in Madison.
UPDATE: According to the WisDOT, the left lane of traffic is now open and the right lane is still closed.
JANESVILLE (WIFR) -- We're told all southbound lanes are blocked on I-39 south at mile post 171 near Janesville due to a crash. The estimated time the road is expected to be blocked is 2 hours. We'll keep you updated as we learn more.