(A) 
Upon all roadways of sufficient width, a vehicle shall be driven upon the right half of the roadway, except as follows:
(1) 
When overtaking and passing another vehicle proceeding in the same direction under the rules governing those movements;
(2) 
When an obstruction exists making it necessary to drive to the left of the center of the roadway; provided, any person so doing shall yield the right-of-way to all vehicles traveling in the proper direction upon the unobstructed portion of the road-way within such distance as to constitute an immediate hazard;
(3) 
Upon a roadway divided into three marked lanes for traffic under the rules applicable thereon;
(4) 
Upon a roadway restricted to one-way traffic;
(5) 
Whenever there is a single-track paved road on one side of the public highway and two vehicles meet thereon, the driver on whose right is the wider shoulder shall give the right-of-way on the pavement to the other vehicle.
(B) 
Upon a two-lane roadway, providing for two-way movement of traffic, a vehicle shall be driven in the right-hand lane available for traffic, or as close as practicable to the right-hand curb or edge of the roadway, except when overtaking and passing another vehicle proceeding in the same direction, or when preparing for a left turn at an intersection or into a private road or driveway.
(C) 
Upon any roadway having four or more lanes for moving traffic, and providing for two-way movement of traffic, no vehicle shall be driven to the left of the center line of the roadway, except when authorized by official traffic-control devices designating certain lanes to the left side of the center of the roadway for use by traffic not otherwise permitted to use the lanes, or except as permitted under division (A)(2). However, this division shall not be construed as prohibiting the crossing of the center line in making a left turn into or from an alley, private road, or driveway.
(ILCS Ch. 625, Act 5, § 11-701(a) -(c))
Drivers of vehicles proceeding in opposite directions shall pass each other to the right and upon roadways having width for not more than one line of traffic in each direction, each driver shall give to the other at least 1/2 of the main traveled portion of the roadway as nearly as possible.
(ILCS Ch. 625, Act 5, § 11-702)
The following rules govern the overtaking and passing of vehicles proceeding in the same direction, subject to those limitations, exceptions, and special rules otherwise stated in this chapter:
(A) 
The driver of a vehicle overtaking another vehicle proceeding in the same direction shall pass to the left thereof at a safe distance, and shall not again drive to the right side of the roadway until safely clear of the overtaken vehicle. In no event shall the movement be made by driving off the pavement or the main traveled portion of the roadway.
(B) 
Except when overtaking and passing on the right is permitted, the driver of an overtaken vehicle shall give way to the right in favor of the overtaking vehicle on audible signal, and shall not increase the speed of his vehicle until completely passed by the overtaking vehicle.
(C) 
The driver of a two-wheeled vehicle may not, in passing upon the left of any vehicle proceeding in the same direction, pass upon the right of any vehicle proceeding in the same direction unless there is an unobstructed lane of traffic available to permit the passing maneuver safely.
(D) 
The operator of a motor vehicle overtaking a bicycle or individual proceeding in the same direction on a highway shall leave a safe distance, but not less than three feet, when passing the bicycle or individual and shall maintain that distance until safely past the overtaken bicycle or individual.
(ILCS Ch. 625, Act 5, § 11-703)
(A) 
The driver of a vehicle with three or more wheels may overtake and pass upon the right of another vehicle only under the following conditions:
(1) 
When the vehicle overtaken is making or about to make a left turn;
(2) 
Upon a roadway with unobstructed pavement of sufficient width for two or more lines of vehicles moving lawfully in the direction being traveled by the overtaking vehicle;
(3) 
Upon a one-way street, or upon any roadway on which traffic is restricted to one direction of movement, where the roadway is free from obstructions and of sufficient width for two or more lines of moving vehicles.
(B) 
The driver of a two-wheeled vehicle may not pass upon the right of any other vehicle proceeding in the same direction unless the unobstructed pavement to the right of the vehicle being passed is of a width of not less than eight feet.
(C) 
The driver of a vehicle may overtake and pass another vehicle upon the right only under conditions permitting the movement in safety. Such movement shall not be made by driving off the roadway.
(ILCS Ch. 625, Act 5, § 11-704)
(A) 
Passing on the left.
(1) 
No vehicle shall be driven to the left side of the center of the roadway in overtaking and passing another vehicle proceeding in the same direction unless authorized by the provisions of this chapter, and unless the left side is clearly visible and is free of oncoming traffic for a sufficient distance ahead to permit the overtaking and passing to be completely made without interfering with the safe operation of any vehicle approaching from the opposite direction, or any vehicle overtaken.
(2) 
In every event, the overtaking vehicle must return to an authorized lane of travel as soon as practicable, and in the event the passing movement involves the use of a lane authorized for vehicles approaching from the opposite direction, before coming within 200 feet of any vehicle approaching from the opposite direction.
(ILCS Ch. 625, Act 5, § 11-705)
(B) 
Conditions where passing on the left is prohibited.
(1) 
No vehicle shall be driven on the left side of the roadway under the following conditions:
(a) 
When approaching or upon the crest of a grade or a curve in the highway where the driver's view is obstructed within a distance as to create a hazard in the event another vehicle might approach from the opposite direction.
(b) 
When approaching within 100 feet of or traversing any intersection or railroad grade crossing.
(c) 
When the view is obstructed upon approaching within 100 feet of any bridge, viaduct, or tunnel.
(2) 
The limitations in division (B)(1) above do not apply upon a one-way roadway, nor upon a roadway with unobstructed pavement of sufficient width for two or more lanes of moving traffic in each direction, nor to the driver of a vehicle turning left into or from an alley, private road, or driveway when the movements can be made with safety.
(ILCS Ch. 625, Act 5, § 11-706)
(A) 
The driver of a vehicle shall stop the vehicle before meeting or overtaking, from either direction, any school bus stopped at any location for the purpose of receiving or discharging pupils. The stop is required before reaching the school bus when there is in operation on the school bus the visual signals as specified in ILCS Ch. 625, Act 5, §§ 12-803 and 12-805. The driver of the vehicle shall not proceed until the school bus resumes motion or the driver of the vehicle is signaled by the school bus driver to proceed or the visual signals are no longer actuated.
(B) 
The stop signal arm required by ILCS Ch. 625, Act 5, § 12-803 shall be extended after the school bus has come to a complete stop for the purpose of loading or discharging pupils and shall be closed before the school bus is placed in motion again. The stop signal arm shall not be extended at any other time.
(C) 
The alternately flashing red signal lamps of an eight-lamp flashing signal system required by ILCS Ch. 625, Act 5, § 12-805 shall be actuated after the school bus has come to a complete stop for the purpose of loading or discharging pupils and shall be turned off before the school bus is placed in motion again. The red signal lamps shall not be actuated at any other time except as provided in division (D) below.
(D) 
The alternately flashing amber signal lamps of an eight-lamp flashing signal system required by ILCS Ch. 625, Act 5, § 12-805 shall be actuated continuously during not less than the last 100 feet traveled by the school bus before stopping for the purpose of loading or discharging pupils within an urban area, and during not less than the last 200 feet traveled by the school bus outside an urban area. The amber signal lamps shall remain actuated until the school bus is stopped. The amber signal lamps shall not be actuated at any other time.
(E) 
The driver of a vehicle upon a highway having four or more lanes which permits at least two lanes of traffic to travel in opposite directions need not stop the vehicle upon meeting a school bus which is stopped in the opposing roadway; and need not stop the vehicle when driving upon a controlled access highway when passing a school bus traveling in either direction that is stopped in a loading zone adjacent to the surfaced or improved part of the controlled access highway where pedestrians are not permitted to cross.
(ILCS Ch. 625, Act 5, § 11-1414(a) - (e))
(A) 
Upon a roadway designated for one-way traffic, a vehicle shall be driven only in the direction designated at all or such times as shall be indicated by official traffic-control devices.
(B) 
A vehicle passing around a rotary traffic island must be driven only to the right of the island.
(C) 
Whenever any highway has been divided into two or more roadways by leaving an intervening space or by a physical barrier or a clearly indicated dividing section so constructed as to impede vehicular traffic, every vehicle must be driven only upon the right-hand roadway unless directed or permitted to use another roadway by official traffic-control devices or police officers. No vehicle may be driven over, across, or within any dividing space, barrier, or section except through an opening in the physical barrier, or dividing section, or space, or at a cross-over or intersection as established by public authority.
(D) 
The driver of a vehicle may turn left across a paved non-curbed dividing space unless prohibited by an official traffic-control device.
(ILCS Ch. 625, Act 5, § 11-708)
(A) 
The City Council is authorized to determine those portions of any highway within the city where overtaking and passing or driving on the left of the roadway would be especially hazardous, and may by appropriate signs or markings on the roadway indicate the beginning and end of the zones, and when signs or markings are in place and clearly visible to an ordinarily observant person, every driver of a vehicle shall obey the directions thereof.
(B) 
Where signs or markings are in place to define a no-passing zone as set forth in division (A) no driver may at any time drive on the left side of the roadway within the no-passing zone or on the left side of any pavement striping designed to mark the no-passing zone throughout its length.
(C) 
This section does not apply under the conditions described in § 71.040 (A)(2), nor to the driver of a vehicle turning left into or from an alley, private road, or driveway. The pavement striping designed to mark the no-passing zone may be crossed from the left-hand lane for the purpose of completing a pass that was begun prior to the beginning of the zone in the driver's direction of travel.
(ILCS Ch. 625, Act 5, § 11-707)
Whenever any roadway has been divided into two or more clearly marked lanes for traffic the following rules in addition to all others consistent herewith shall apply.
(A) 
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.
(B) 
Upon a roadway which is divided into three lanes and provides for two-way movement of traffic, a vehicle shall not be driven in the center lane except when overtaking and passing another vehicle traveling in the same direction when such center lane is clear of traffic within a safe distance, or in preparation for making a left turn or where such center lane is at the time allocated exclusively to traffic moving in the same direction that the vehicle is proceeding and such allocation is designated by official traffic-control devices.
(C) 
Official traffic-control devices may be erected directing specific traffic to use a designated lane or designating those lanes to be used by traffic moving in a particular direction regardless of the center of the roadway and drivers of vehicles shall obey the directions of every such device. Drivers must obey lane designation signing except when it is necessary to use a different lane to make a turning maneuver.
(D) 
Official traffic-control devices may be installed prohibiting the changing of lanes on sections of roadway and drivers of vehicles shall obey the directions of every such device.
(ILCS Ch. 625, Act 5, § 11-709)