Quick answer
Uninsured motorist (UM) coverage pays for injuries caused by a driver with no insurance, and underinsured motorist (UIM) coverage pays when the at-fault driver’s insurance is not enough to cover the losses.[1] The III reports that an estimated 15.4% of U.S. drivers were uninsured in 2023.[2] UM coverage is mandatory in about 20 jurisdictions.[2]
What UM and UIM coverage are
According to the III, uninsured motorist coverage reimburses the policyholder for injuries caused by an uninsured or hit-and-run driver, and underinsured motorist coverage applies when the at-fault driver has insurance but not enough to pay for the losses.[1] The claim is made to the injured person’s own insurer.
How common uninsured drivers are
The III, citing the Insurance Research Council, reports that about 15.4% of drivers were uninsured in 2023, up from 14.0%, or about one in seven, in 2022.[2]
Where it is required
The III reports that uninsured motorist coverage is mandatory in about 20 jurisdictions.[2] Requirements in other states are set by each state’s insurance law.
Why it matters for head injuries
State minimum liability limits can be low compared with the cost of a serious head injury. The CDC reports more than 214,000 TBI-related hospitalizations in 2020,[3] and a severe TBI can lead to long-term rehabilitation. When the at-fault driver’s limits are exhausted, UIM coverage may be the remaining source of payment.
UM claims and work injuries
Courts have addressed how UM coverage interacts with workers’ compensation. In 2024, the Colorado Supreme Court held that an employee receiving workers’ compensation after a crash caused by an underinsured driver was not barred from suing the employer’s UM/UIM carrier.[4]
How UM claims differ from liability claims
In a UM or UIM claim, the injured person’s own insurer steps into the shoes of the at-fault driver and can dispute fault and the extent of the injury, just as a liability insurer would. Policies can also set conditions such as notice and cooperation requirements, so the policy wording matters.
Frequently asked questions
Does UM cover hit-and-run crashes?
The III says uninsured motorist coverage can apply to injuries caused by a hit-and-run driver.[1]
How many drivers are uninsured?
The III reports an estimated 15.4% in 2023.[2]
This page provides general information about the law from the sources listed below. It is not legal advice, and reading it does not create an attorney-client relationship. Laws vary by state and change over time. See our legal disclaimer.
Sources
- Insurance Information Institute. “What is covered by a basic auto insurance policy?” https://www.iii.org/article/what-covered-basic-auto-insurance-policy
- Insurance Information Institute. “Background on: Compulsory auto/uninsured motorists.” https://www.iii.org/article/background-on-compulsory-auto-uninsured-motorists
- Centers for Disease Control and Prevention. “TBI Data.” https://www.cdc.gov/traumatic-brain-injury/data-research/index.html
- NCCI. “Court Case Update, Colorado and Nevada – October 2024.” https://www.ncci.com/Articles/Pages/Insights_CourtCase_Update_CO_NV_October2024.aspx
Sources last checked: October 11, 2026
