Mile marker numbering on I-94 Business Loops in North Dakota

[jasonh300]

Anyone know how the Business Loops of I-94 in North Dakota are numbered?  All of the mile markers are in the 800s and 900s.  I know these six business loops are former alignments of the mostly defunct US-10, so I wonder if the numbers are based on the total mileage of the original US-10 route, crossing state lines.  Any ideas?

[NE2]

http://www.dot.nd.gov/docs/maps/state/2015CDRS_Combined.pdf
Each one picks up roughly where the previous one leaves off.

[jasonh300]

http://www.dot.nd.gov/docs/maps/state/2015CDRS_Combined.pdf
Each one picks up roughly where the previous one leaves off.

I see.  I didn't realize it was that simple.  So it starts from the first business route at the west end of Medora at 900.  Why 900? Is that something specific to North Dakota, or is this done elsewhere?  We don't have Interstate business routes down south, so this is my first experience with them.  I remember finding a similarly high mile marker on a US highway in southern Alabama, but I don't remember the details, so I never was able to find out what the deal was with that either.

[Scott5114]

It may just be an arbitrary starting point to avoid conflict with numbering on mainline I-94.

Texas mileposts are all measured from an arbitrary zero point in New Mexico that no Texas highway actually reaches. It could also be something like that.