1. All vehicles not in motion shall be placed with their right side as near the right-hand side of the highway as practicable, except on streets of municipalities where vehicles are obliged to move in one direction only or parking of motor vehicles is regulated by ordinance.

2. Upon all public roads or highways of sufficient width a vehicle shall be driven upon the right half of the roadway, except as follows:

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(1) When overtaking and passing another vehicle proceeding in the same direction pursuant to the rules governing such movement;

(2) When placing a vehicle in position for and when such vehicle is lawfully making a left turn in compliance with the provisions of sections 304.014 to 304.025 or traffic regulations thereunder or of municipalities;

(3) When the right half of a roadway is closed to traffic while under construction or repair;

(4) Upon a roadway designated by local ordinance as a one-way street and marked or signed for one-way traffic.

3. It is unlawful to drive any vehicle upon any highway or road which has been divided into two or more roadways by means of a physical barrier or by means of a dividing section or delineated by curbs, lines or other markings on the roadway, except to the right of such barrier or dividing section, or to make any left turn or semicircular or U-turn on any such divided highway, except at an intersection or interchange or at any signed location designated by the state highways and transportation commission or the department of transportation. The provisions of this subsection shall not apply to emergency vehicles, law enforcement vehicles or to vehicles owned by the commission or the department.

4. The authorities in charge of any highway or the state highway patrol may erect signs temporarily designating lanes to be used by traffic moving in a particular direction, regardless of the center line of the highway, and all members of the Missouri highway patrol and other peace officers may direct traffic in conformance with such signs. When authorized signs have been erected designating off-center traffic lanes, no person shall disobey the instructions given by such signs.

5. Whenever any roadway has been divided into three or more clearly marked lanes for traffic, the following rules in addition to all others consistent herewith shall apply:

(1) A vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety;

(2) Upon a roadway which is divided into three lanes a vehicle shall not be driven in the center lane, except when overtaking and passing another vehicle where the roadway ahead is clearly visible and such center lane is clear of traffic within a safe distance, or in preparation for a left turn or where such center lane is at the time allocated exclusively to traffic moving in the direction the vehicle is proceeding and is sign-posted to give notice of such allocation;

(3) Upon all highways any vehicle proceeding at less than the normal speed of traffic thereon shall be driven in the right-hand lane for traffic or as close as practicable to the right-hand edge or curb, except as otherwise provided in sections 304.014 to 304.025;

(4) Official signs may be erected by the highways and transportation commission or the highway patrol may place temporary signs directing slow-moving traffic to use a designated lane or allocating specified lanes to traffic moving in the same direction and drivers of vehicles shall obey the directions of every such sign;

(5) Drivers of vehicles proceeding in opposite directions shall pass each other to the right, and except when a roadway has been divided into traffic lanes, each driver shall give to the other at least one-half of the main traveled portion of the roadway whenever possible.

6. All vehicles in motion upon a highway having two or more lanes of traffic proceeding in the same direction shall be driven in the right-hand lane except when overtaking and passing another vehicle or when preparing to make a proper left turn or when otherwise directed by traffic markings, signs or signals.

7. All trucks registered for a gross weight of more than forty-eight thousand pounds shall not be driven in the far left-hand lane upon all interstate highways, freeways, or expressways within urbanized areas of the state having three or more lanes of traffic proceeding in the same direction. This restriction shall not apply when:

(1) It is necessary for the operator of the truck to follow traffic control devices that direct use of a lane other than the right lane; or

(2) The right half of a roadway is closed to traffic while under construction or repair.

8. As used in subsection 7 of this section, “truck” means any vehicle, machine, tractor, trailer, or semitrailer, or any combination thereof, propelled or drawn by mechanical power and designed for or used in the transportation of property upon the highways. The term “truck” also includes a commercial motor vehicle as defined in section 301.010.

9. Violation of this section shall be deemed a class C misdemeanor unless such violation causes an immediate threat of an accident, in which case such violation shall be deemed a class B misdemeanor, or unless an accident results from such violation, in which case such violation shall be deemed a class A misdemeanor.