These routes connect a central or commercial district of a city or town with an Interstate bypass.

In many eastern states, the new Interstates were often built to parallel the existing U.S. Highway network, rather than directly replacing those older routes.

However, in the western states, the construction of the Interstate system more frequently involved directly overlaying the former U.S. Highway alignments.

To maintain access to those former highway segments, business Interstate designations were often applied as a way to guide drivers to key commercial districts and services.

Business Interstates are often designated along existing city streets or arterials that already have a strong commercial and retail presence, rather than cutting through the urban core on a new alignment.

They are treated more as auxiliary or supplemental routes that complement the overall Interstate network, rather than being fully integrated components.

While they aim to maintain a baseline of safety and continuity, the standards are less stringent than the exacting specifications for lane widths, access control, grade separations, and other factors that define the main Interstate Highway network.

One example includes all the I-5 business loops in northern California, which replaced US 99W through towns like Woodland, Arbuckle, or Williams.