Traffic lanes are not as simple as they first appear. When you start off driving, at the young innocent age of 16, you see two lanes of traffic; one going one way, another going the opposite. That may be the case for some simple roads, but often it can get much more complicated. You should familiarize yourself with the many different types of traffic lanes, so you can be prepared next time you see them.
It is important to learn about passing lanes, particularly if you are going to be doing any traveling in between cities. Single lane highways are common. There will be one lane for each direction of traffic. These lanes will be separated by a solid line. As a rule, you can never cross solid lines with your car. Treat them as if they were a brick wall. Dotted lines can be passed over. Streets and highways with multiple lanes separate their lanes using dotted lane lines. You can pass over these freely.
There are complicated lanes out there. In a reversible lane, traffic can flow in either direction depending on the time of day. This is typically dictated by peak flow times and rush hour. A reversible lane should be marked overhead and on the street itself. HOV lanes, or high occupancy vehicle lanes, are becoming popular in large cities. These lanes are designated only for vehicles with more than one occupant. Because of this, there is typically less traffic in HOV lanes.
With 26 lanes, the Katy Freeway is the widest in the world. It was built in the 1960s and now sees over 219,000 vehicles a day passing over its surface. This section of the I-10 actually possesses 6 HOV lanes, 12 main lanes, and 8 lanes of access roads.