Written and reviewed by Tarihya J. McClain, Managing Attorney
Last reviewed: August 19, 2026
The Missouri HB 1740 DWI law changes take effect August 28, 2026. The legislation changes when some drivers may be required to use a certified ignition-interlock device, creates a reduced-cost option for qualifying drivers, establishes a child-maintenance process after certain fatal impaired-driving offenses, and revises penalties for DWI offenses involving injury or death.
A Missouri DWI can create both a criminal case and a separate driver’s-license matter. The new law does not affect every arrest in the same way. A driver’s history, test results, alleged facts, licensing action, and the final outcome of the case can all affect which provisions apply.
What does Missouri HB 1740 change?
Missouri HB 1740 makes four major changes:
- It expands ignition-interlock requirements for certain DWI convictions involving a high blood-alcohol concentration, a prior alcohol-related enforcement contact, property damage, or personal injury.
- It provides an income-based discount for qualifying ignition-interlock users.
- It revises felony classifications and minimum incarceration provisions for certain injury-related and fatal DWI offenses.
- It creates “Bentley and Mason’s Law,” which may require child-maintenance payments when an impaired-driving offense causes the death of a child’s parent or guardian.
These are significant changes, but an arrest alone does not establish that every provision will apply.
Expanded ignition-interlock requirements
An ignition-interlock device requires a driver to provide a breath sample before a vehicle will start. Missouri already uses these devices in several DWI and license-reinstatement situations. Missouri HB 1740 expands those requirements.
Under the new law, proof of a functioning, certified ignition-interlock device may be required as a condition of license reinstatement or certain restricted driving privileges when the driver’s record involves:
- A qualifying intoxication-related conviction with a blood-alcohol concentration of at least .08% but below .15% and a prior alcohol-related enforcement contact;
- A qualifying conviction involving a blood-alcohol concentration of .15% or higher; or
- A qualifying offense in which the driver caused property damage or personal injury.
The law also expands circumstances in which a court must require an interlock following a conviction. Because these provisions depend on specific statutory definitions and procedural events, they should not be read to mean that every first DWI arrest automatically produces the same requirement.
How long may an ignition interlock be required?
When the new provisions apply, the device generally must be maintained on every vehicle operated by the person for at least six months following license reinstatement.
The period may be extended if monitoring reports show a confirmed alcohol reading above the established setpoint or show that the device was tampered with or circumvented during the final three months. The driver may then need to complete three consecutive months without a reported violation.
Failing to maintain the required proof can result in another suspension or revocation and may constitute a Class A misdemeanor. Drivers should keep copies of installation, monitoring, compliance, and removal records and confirm that the provider is properly reporting to the state.
Financial assistance for qualifying drivers
Missouri HB 1740 requires certified interlock providers to offer a discounted fee schedule for individuals whose income is at or below 150% of the federal poverty level.
A qualifying person who provides the required income verification is responsible for 10% of the device’s cost. Verification may include:
- The previous year’s federal income-tax return;
- The previous three months of weekly or monthly income statements; or
- A court order establishing that the person’s income falls within the qualifying limit.
Additional expenses caused by noncompliance are not included in the discount.
Changes involving physical injury, serious injury, or death
Missouri HB 1740 revises how Missouri classifies certain injury- and death-related DWI offenses under Section 577.010.
Among the changes, the law places a DWI involving criminally negligent physical injury to another person within the Class D felony provisions and a DWI involving criminally negligent serious physical injury within the Class C felony provisions. It also restructures the Class B and Class A felony provisions involving death and habitual-offender status.
The final legislation includes minimum periods during which a person convicted of specified fatal-DWI offenses is not eligible for parole or probation: at least five years for the specified Class B offense and at least ten years for a Class A offense.
This does not mean every accident connected to a DWI allegation results in one of these charges. The prosecution must establish the elements of the charged offense, and the proper classification depends on the facts and applicable law.
What is Bentley and Mason’s Law?
Missouri HB 1740 also creates a child-maintenance procedure known as “Bentley and Mason’s Law.”
When a person is convicted of or enters a qualifying plea to DWI or driving with excessive blood-alcohol content, the offense caused the death of a child’s parent or guardian, and a surviving parent or guardian files a petition, a court may order the convicted person to pay maintenance for the child.
The statute provides factors for determining the amount and duration of the obligation. It also addresses incarceration, unpaid amounts, civil judgments, and other circumstances that may affect an order. The maintenance requirement is not automatically imposed after every fatal crash; the statutory requirements and court process must be satisfied.
What should someone do after a Missouri DWI arrest?
Read every document received from the officer. A DWI arrest may create a criminal case and a separate license matter, each with its own procedures and deadlines.
- Save the Form 2385, temporary permit, bond paperwork, and court information.
- Write down what happened while the events are still fresh.
- Confirm whether and for how long you may legally drive.
- Avoid assumptions based only on what happened in another person’s case.
- Speak with a Missouri DWI defense attorney promptly about the specific deadlines and available options.
An arrest is not a conviction. The facts, evidence, testing procedures, driving history, and timing can all affect the analysis.
Frequently asked questions about Missouri HB 1740
Does every first Missouri DWI require an ignition interlock?
No. HB 1740 expands the circumstances in which an interlock is required, including certain cases involving a BAC of .15% or higher, property damage, or personal injury. Courts may also impose interlock requirements in other situations. The precise requirement depends on the conviction, licensing action, and driving history.
What if I cannot afford an ignition-interlock device?
A person with income at or below 150% of the federal poverty level may qualify to pay 10% of the device cost after providing acceptable income verification. Costs resulting from noncompliance are not included in that discount.
How long will I need the interlock?
When the new provisions apply, the minimum period is generally six months following reinstatement. A violation or tampering report during the final three months can extend the requirement.
Does installing an interlock resolve the criminal DWI case?
No. An interlock requirement may relate to driving privileges, reinstatement, a restricted privilege, or a court order. It does not by itself resolve the criminal charge.
Does HB 1740 apply to an arrest before August 28, 2026?
The effective date alone does not answer which provisions govern a particular matter. The date of the alleged conduct, the type of proceeding, and other legal considerations may matter. An attorney should review the individual timeline.
Are all DWI crashes now felonies?
No. A felony classification depends on the elements charged and proven, including injury, causation, criminal negligence, prior-offender status, and other facts. Every case requires an individual evaluation.
Talk with McClain Law
If you have been arrested for DWI or are trying to understand an ignition-interlock, restricted-driving, or license-reinstatement issue, McClain Law can review the circumstances and explain the available options.
McClain Law, LLC
Phone: (314) 970-5159
Email: t.mcclain@mcclain.law
Schedule a free 15-minute consultation
Official sources: Read the Missouri Senate bill summary and the final enacted text of HB 1740.
Related Missouri driving resources
- What to do in the first 15 days after a Missouri DWI arrest
- Missouri SB 1408: the new 75 mph maximum speed limit
- How Missouri driver’s-license points work
- Should you simply pay a Missouri traffic ticket?
Disclaimer: This post is for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Laws and their application can change, and every matter depends on its individual facts.