Kentucky number is a tax license number issued for the Kentucky Weight Distance Tax. Any carrier over 59,999 lbs traveling in Kentucky is subject to this tax. The difference between a NM and a KY permit is that you must apply for KYU Number and display it on your truck just like your MC and US DOT numbers. Quarterly returns are also required and each vehicle should be reported. If you apply for KYU Number as a motor carrier and not as a vehicle owner / registrant, you must have your US DOT, MC authority, and UCR active / paid for. Then it takes a few days to obtain the license. KYU permit never expires.