Illinois laws regulate and detail how drivers are supposed to act in traffic. These are so-called “Rules of the Road“, part of which explains how to properly, lawfully and safely use lanes.

Drivers must drive on the right half of the roadway except:

• When passing another vehicle moving in the same direction on a two-lane highway, interstate highway or controlled freeway.
• When a blockage makes it necessary to drive to the left of the center line. Drivers may drive on the left after yielding to oncoming traffic.
• On a roadway divided into three marked lanes for traffic.
• On a one-way street with two or more lanes of traffic.
• When directed to drive in a left lane by traffic control signs and signals on a multilane, two-way highway.
• When crossing the center line to make a left turn into or from an alley, private road or driveway.
• When approaching a stationary emergency vehicle.
• When roadway construction is located in or in close proximity to the right lane or right shoulder.

When driving on an interstate highway or full access controlled freeway, a driver may not drive in the left lane(s), except when passing another vehicle. Exceptions include when:

• No other vehicle is directly behind the vehicle being driven in the left lane.
• Traffic conditions/congestion make it impractical to drive in the right lane.
• Weather conditions make it necessary to use the left lane(s).
• There is an obstruction or hazard in the right lane.
• The driver is changing lanes to yield to emergency or construction vehicles.

Additional rules apply in certain situations:

• Slow vehicles must use the right-hand lane except when passing vehicles or making a left turn.
• Weaving from lane to lane to move faster than the traffic flow is unlawful.
• Traffic must travel in the direction of posted one-way streets or roadways. This rule does not apply to police and emergency vehicles using sirens or flashing lights.
• It is unlawful to drive across median strips such as unpaved strips or median barriers. A driver may turn left across a paved dividing-space unless it is not permitted by a traffic control sign or signal.
• A driver must not enter or leave any controlled-access roadway except at a posted entrance or exit.
• A driver may not back up on any shoulder or roadway of any controlled access roadway.
• A driver may not back up on other roadways unless it is done safely and does not interfere with other vehicles.
• A driver or passenger may not open doors on the side of a vehicle on which traffic is moving unless it can be done safely and without interfering with traffic. The door may remain open only long enough to load or unload passengers.