Highways and interstates are chock-full of vehicles: slow and fast, large and small, all with different places to be. The left lane is designed to make the road more efficient, letting fast-moving traffic pass slower vehicles.
You’ve probably been frustrated before by a semi-truck hogging the left lane. They take up space and move more slowly.
When, where and why is it permissible for a commercial vehicle to drive in the left lane?
What Is the “Hammer Lane” and Why Do Truckers Use It?
The far-left lane, or the passing lane, is often referred to by truckers as the “hammer lane” because it requires higher-than-normal speed. Generally, large trucks are encouraged or required to stay out of this lane.
Commercial motor vehicles must follow lower speed limits than passenger vehicles, and some trucking companies use speed limiters in their trucks to eliminate dangerous behavior. For these reasons, semis rarely have to use the leftmost lane.
There are a few situations where large trucks are permitted in the hammer lane. We’ll dive into that later. First, what makes these situations risky?
Why Large Trucks in the Left Lane Pose a Serious Safety Risk
Commercial motor vehicles can endanger cars and small trucks when they hang out in the passing lane. If they drive below or at the speed limit, they can cause traffic congestion. Cars become stuck behind the large truck until it moves back over.
Or, if a semi-truck keeps up with the pace of the left lane, it likely exceeds the speed limit — another dangerous behavior. When traveling at high speeds, truckers can lose control of their rigs and swerve off the road or into another lane, rear-end drivers, or overturn.
We’ve previously discussed that large trucks have significant blind spots, which prevent their drivers from seeing surrounding vehicles. But did you know that, out of all of a semi tractor-trailer’s blind spots — front, side and rear — the right-side blind spot is by far the largest?
Because the truck driver sits on the left side of the vehicle, everything to the right is farther away. Whereas the left-hand blind spot extends from the door of the cab to the middle of the trailer, the blind spot on the right obscures the entire length of the trailer.
So, when a trucker drives in the left lane, he cannot see any vehicles within that area in the lane to the right. If he tries to get back into the right lane, he runs the risk of striking another vehicle. This can result in underride, a common and often deadly type of crash.
Lane Restriction Violations: How They Impact Trucking Companies
Trucking companies in the U.S. are held to Compliance, Safety and Accountability (CSA) standards. Their CSA scores are negatively affected when their drivers violate safety standards. Distracted driving, speeding, and even following too closely are among the possible violations.
These dangerous behaviors can then be identified and logged during roadside inspections. This is designed to hold truckers accountable and monitor their compliance with safety standards.
“Lane restriction violations” fall within the “unsafe driving” category. If a semi driver is caught misusing the left lane, his company’s CSA score can be raised by three points. High CSA scores indicate that a trucking company is unsafe.
The Federal Motor Carrier Safety Administration provides data on these roadside inspection violations. Between 2020 and 2024, lane restriction violations ranked sixth out of 354 as one of the most common types of violation.
There were 171,369 lane restriction violations total, making up 3.6% of all violations in that time period.
In Indiana and Illinois, this was the third most common violation between 2020 and 2024. It ranked fifth in Kentucky and tenth in Tennessee.
State Laws on Left-Lane Truck Restrictions: What Drivers Need to Know
Every state regulates left-lane usage. Some focus on commercial motor vehicles or specific types of large trucks, while others restrict the left lane for all traffic, including passenger vehicles.
At Craig, Kelley & Faultless, our truck-wreck attorneys are licensed in various states across the country. It is important for drivers to know the rules and regulations of states through which they travel. Let’s look at a few.
Indiana Left-Lane Laws
Indiana law states that trucks, truck tractors, road tractors, trailers, semi-trailers and pole trailers must use the far right lane on interstate highways. Left-lane travel is allowed when these vehicles are passing slower traffic, entering or exiting a highway, or avoiding special hazards.
It also instructs all drivers traveling under the speed limit to stay in the right lane except when weather, traffic, or construction requires them to use the left lane. They can also use the left lane to exit, turn, or yield to emergency vehicles.
Missouri Trucking Laws
According to Missouri law, trucks weighing over 48,000 pounds may not use the left lane on roads with three or more lanes unless they are following traffic control devices or forced into the left lane due to lane closures.
Missouri defines “truck” as a vehicle/tractor/trailer/machine or other commercial motor vehicle used for hauling property.
Other vehicles should stick to the right lane unless passing someone, making a left turn, or avoiding work zones.
Illinois Left-Lane Rules
Illinois law does not single out large trucks; rather, it limits left-lane use for all vehicles, regardless of size or type.
In this state, all vehicles are required to drive on the right half of the roadway, except when:
- Passing a slower vehicle
- Avoiding an obstacle or hazard
- Preparing for a left turn
- Weather or traffic congestion require drivers to use the left lane
Kentucky’s Left-Lane Restrictions for Trucks and Passenger Vehicles
In Kentucky, on highways with four or more lanes and a speed limit of 65 miles per hour or greater, all vehicles should stay out of the left lane unless they are passing a slower vehicle, yielding to traffic entering the highway, or when it is not safe to use other lanes.
On other roads, vehicles may use the left lane to pass or make a turn when it is safe to do so, or when signs direct them to the left lane.
Ohio’s Left-Lane Regulations for Safer Highways
Ohio does not specifically address commercial motor vehicles in its left-lane regulations. Instead, its laws state that all vehicles should travel on the right half of the roadway. Exceptions occur when drivers need to pass a slower vehicle, avoid an obstacle in the road, prepare for a left turn, or follow the directions of a police officer or traffic control device.
Iowa’s Left-Lane Laws
Like other states, Iowa restricts left-lane travel to those vehicles that must pass slower vehicles, avoid an obstruction in the right lane, or prepare for a left turn.
Tennessee Left-Lane Laws
This state shares similar restrictions: Vehicles should stay on the right half of the roadway, unless they are passing a vehicle, navigating around construction, or preparing to turn left.
In 2020, Tennessee revised its “Slow Poke Law” to prohibit passenger vehicles from spending more time than necessary in the left lane, in order to protect truckers.
How to Stay Safe Around Semi-Trucks in the Left Lane
If you’re a truck driver, the safest thing to do is obey each state’s guidelines for left-lane usage. Unless absolutely necessary, drive at a safe speed in a right-hand lane. Be aware of your blind spots.
As a car driver, use caution when passing (or being passed by) a semi-truck. If you’re behind a slow truck in the passing lane, avoid speeding and aggressive driving. And remember: Just because you can see a semi, that doesn’t mean its driver can see you.
If you are the victim of a wreck caused by a commercial motor vehicle driver’s carelessness, you must reach out to a qualified attorney. Craig, Kelley & Faultless has certified and experienced truck-wreck lawyers ready to help victims of serious injury or death.
Injured in a Truck Accident? Legal Help Is Available
David W. Craig sits on the Board of Regents of the Academy of Truck Accident Attorneys (which requires the board certification in truck accident law). He is the managing partner and one of the founding partners of Craig, Kelley & Faultless LLC. He is recognized as a Top 10 Trucking Trial Lawyer and Top 100 Trial Lawyer in Indiana by the National Trial Lawyers, as well as a Top 50 Indiana lawyer by Super Lawyers. David is the author of Semitruck Wreck, A Guide for Victims and Their Families, written to help people navigate a terrible situation by answering questions that come after a tragic wreck. He also hosts the podcast After the Crash, where you can gain valuable information about the dangers involving semis and large trucks that do not follow Indiana law safety protocol regarding speed, weather conditions, maintenance upkeep, etc.
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