The 24th Street off-ramp from Northbound 99 closed early Wednesday morning.
Caltrans crews shut down the off-ramp as construction begins to add another lane onto the exit.
Caltrans says the exit will be closed for 55 days.
It suggested that drivers use the California Avenue or Buck Owens exits as detours.
The Buck Owens on-ramp is also closed for 55 days.
