How and why do you use what you have?
Here at NCDOT, we currently use an 11 digit number. The first 8 digits have been in place for decades (1960's or earlier). The last three have only changed slightly from 2 digits before R&H. That change brought the LRS group in compliance with the rest of the enterprise.
For County LRM:
For State LRM (designated state highways only):
I have some SQL that will partition distinct road name parts by city and county to row number local route IDs into a 4 or 5 character route ID, I'd be glad to share it if anyone has an appetite for looking at SSMS update query statements. Once that Route ID is assigned for locals, we dissolve connected segments, and partition by route ID to calculate unique ID's for local gapped routes from row numbers. We had about 6 routes with more than 100 gapped route ID segments in our local roads so we manually changed some of those route IDs to keep the unique ID to two characters.