Is it legal to drive slow in the left lane in IL, MO? When you can use the passing lane
Those who regularly cross the Illinois-Missouri state line may want to keep in mind the states have different rules about when drivers can lawfully use the left lane.
The Land of Lincoln has a few more exceptions for when it’s legal to drive in the left lane, but both states generally require vehicles to stay to the right unless special conditions are met.
Here’s what to know about traffic laws in Illinois and Missouri on use of the left lane.
When can you use the left lane in Illinois?
Illinois law says drivers can only use the left lane on the interstate while passing another vehicle or in the following circumstances:
When no other vehicle is directly behind the vehicle in the left lane
When traffic conditions or congestion make it impractical to drive in the right lane
When snow or inclement weather conditions make it necessary to drive in the left lane
When there are obstructions or hazards in the right lane
When a vehicle must be in the left lane to exit
There are also other exceptions, such as when drivers must change lanes to pay a toll or comply with traffic control. Emergency vehicles and construction workers may also use the left lane when necessary.
What about in Missouri?
In Missouri, drivers must use the right side of “public roads or highways of sufficient width” unless they are:
Passing or overtaking another vehicle going in the same direction
When the vehicle is positioning for a lawful left turn
When the right lane is closed to traffic for construction or repairs
On a one-way road
The Missouri law, which was last updated in 2010, says violations result in at least a Class C misdemeanor. If a violation causes an “immediate threat of an accident,” it results in a Class B misdemeanor, and if it causes an accident, it’s deemed a Class A misdemeanor.
Laws on slow driving in Illinois and Missouri
Illinois law says: “No person shall drive a motor vehicle at such a slow speed as to impede or block the normal and reasonable movement of traffic except when reduced speed is necessary for safe operation of his vehicle or in compliance with law.”
The regulation covers Illinois drivers generally, not just when using the left lane. Minimum speed limits may be established on Illinois roads where slow drivers “consistently impede” the normal traffic flow.
Missouri has a very similar provision to Illinois: “No person shall drive a motor vehicle at such a slow speed as to impede or block the normal and reasonable movement of traffic, except when reduced speed is necessary for safe operation or in compliance with law.”
Additionally, the Missouri law says no vehicles may be operated at a speed less than 40 miles per hour on roads that are part of interstate highways unless:
- “A slower speed is required for the safe operation of the vehicle because of weather or other special conditions; or
- Agricultural implements, self-propelled hay-hauling equipment, implements of husbandry and vehicles transporting such vehicles or equipment may be operated occasionally on interstate highways for short distances at a speed of less than forty miles per hour if such vehicle or equipment is operated pursuant to a special permit issued by the chief engineer of the state department of transportation pursuant to section 304.200 and the regulations established pursuant to such section.”
Violating the 40 mile per hour minimum speed on Missouri interstate highways can result in a Class C misdemeanor. This Missouri law is also a general traffic regulation and does not apply exclusively to left lanes.
