where are you?

Fourteen states require underinsured motorist coverage (UIM): Connecticut, Maine, Maryland, Massachusetts, Minnesota, Nebraska, New Jersey, North Carolina, North Dakota, Oregon, South Dakota, Vermont, Virginia, and Wisconsin. UIM compensates a policyholder when the at-fault driver has an insufficient amount of auto liability insurance.

https://www.cga.ct.gov/2013/rpt/2013-r-0258.htm?

This report is dated 2013.  Now it could be different.