The Bx endorsement lets you haul two or three trailers at once in Michigan

The Bx endorsement on a Michigan commercial driver's license allows you to tow double or triple trailers — meaning you can pull two or three trailers behind a single power unit. Without it, you are limited to pulling one trailer. This endorsement is specific to Michigan and is not recognized in other states, so you can only use it within Michigan borders.

The Bx is different from the more common doubles/triples endorsement you might see in other states. Michigan's version has its own rules about vehicle weight, configuration, and where you can operate. If you haul multiple trailers for a living in Michigan, you need this endorsement on your CDL before you can legally do that work.

Key Takeaways

  • The Bx endorsement allows you to tow two or three trailers in Michigan only; it is not valid in other states.
  • You must pass a written knowledge test specific to doubles and triples operations before the Secretary of State will add the Bx to your CDL.
  • Your vehicle must meet Michigan's weight and length limits for doubles and triples configurations, which differ from single-trailer limits.
  • The Bx endorsement costs a fee when you add it to your license; the amount varies and you should confirm the current fee with your local Secretary of State office.

Who needs the Bx endorsement

You need the Bx endorsement if your job requires you to operate a vehicle towing two or three trailers on Michigan roads. This includes drivers for trucking companies that run doubles or triples routes, owner-operators who haul multiple trailers, and drivers for freight or logistics companies that use multi-trailer configurations.

If you currently hold a Michigan CDL with only a single-trailer endorsement and your employer asks you to haul doubles or triples, you cannot legally do that work until you add the Bx. Operating without the proper endorsement is a violation and can result in fines and points on your record.

How to add the Bx endorsement to your Michigan CDL

To add the Bx endorsement, you must visit a Secretary of State office that handles CDL transactions. Bring your current Michigan CDL, proof of residency, and a valid form of identification. You will need to pass a written knowledge test that covers doubles and triples operations, vehicle configurations, weight distribution, and safe handling practices specific to multi-trailer rigs.

The test is administered at the Secretary of State office on the day you explore. You do not need to schedule in advance at most locations, but calling ahead to confirm hours and current wait times is a good idea. Once you pass the test, the Secretary of State will add the Bx endorsement to your license and collect the endorsement fee. Your updated CDL will be mailed to you within a few weeks.

What the knowledge test covers

The Bx knowledge test focuses on the mechanics and safety of operating doubles and triples. You will be asked about proper coupling and uncoupling procedures, how to inspect multi-trailer rigs, weight limits and load distribution, braking systems on doubles and triples, and how to handle emergency situations like jackknife or trailer sway.

The test also covers Michigan-specific rules about where doubles and triples can operate. For example, certain roads and highways have restrictions on multi-trailer vehicles, and you need to know those limits. The test is multiple-choice and you must score a passing grade — typically 80 percent or higher, though you should confirm the exact passing score with your local Secretary of State office.

You can study using the Michigan CDL manual, which includes a section on doubles and triples operations. Many drivers also use online practice tests or study guides designed for the Bx endorsement. Taking time to prepare before you test increases your chances of passing on the first attempt.

Vehicle requirements for doubles and triples in Michigan

Your vehicle must meet specific weight and dimension limits to legally operate as a doubles or triples rig in Michigan. The gross vehicle weight rating (GVWR) and overall length of the combination are regulated, and exceeding those limits is illegal even if you hold the Bx endorsement.

Michigan also has rules about the types of trailers you can tow and how they must be connected. Air brake systems are required on all trailers in a doubles or triples combination, and your power unit must have compatible brakes. Your employer or the company that owns the equipment should confirm that all vehicles meet Michigan's specifications before you operate them.

Bx endorsement fees and renewal

The fee to add the Bx endorsement to your CDL varies and changes periodically. You should contact your local Secretary of State office to learn the current cost. The endorsement is valid for the same period as your CDL — typically four or eight years depending on your age and whether you are a hazmat driver.

When you renew your CDL, you will need to renew the Bx endorsement as well. You may be required to retake the knowledge test at renewal, depending on Michigan's current rules. Some drivers renew by mail or online, but endorsement renewals typically require an in-person visit to a Secretary of State office.

Frequently Asked Questions

Can I use my Bx endorsement in other states?

No. The Bx endorsement is valid only in Michigan. If you cross state lines, you cannot tow doubles or triples in other states unless you hold that state's equivalent endorsement. Many drivers who work across state lines hold multiple endorsements from different states.

What happens if I drive doubles or triples without the Bx endorsement?

Operating a multi-trailer vehicle without the proper endorsement is a violation of Michigan law. You can be cited, fined, and receive points on your driving record. Your employer can also face penalties. If you are involved in a crash while operating without the endorsement, your insurance may deny coverage.

Do I need to pass a skills test for the Bx endorsement?

Michigan requires a written knowledge test for the Bx endorsement. Some states also require a behind-the-wheel skills test for doubles and triples, but you should confirm Michigan's current requirements with the Secretary of State. Your employer may require additional training or testing beyond what the state mandates.

How long does it take to get the Bx endorsement added to my CDL?

The knowledge test is administered the same day you visit the Secretary of State office. Once you pass, the endorsement is added to your record when ready, but your updated physical CDL card is mailed to you, which typically takes two to four weeks. You can usually begin operating doubles and triples once you pass the test, even before the new card arrives.