Powerinroads design speed for superelevation can not choose below 50 km/h

I want use the" AASHTO 2001 emax6 Dual metric.srl" file to do superelevation, but the design speed for superelevation can not display for choose below 50 km/h, but the file list all the speed, does any body know how to show the 40km/h speed for use?

if i change to "AASHTO 2001 emax4 metric.srl", the 40km/h speed is display for choose.