Lanes of traffic moving in opposite directions are separated by yellow lines. On the other hand white lines indicate separation of lanes of traffic traveling in the same direction. Red and blue colors are used to indicate different road signage and do not typically separate traffic lanes.

A driver is only permitted to pass another car on a two lane highway when a broken white line is present. As a general rule, solid lines indicate that cars cannot pass one another. On the other hand, broken lines indicate that vehicles may pass one another. Engineers may decide that curvy roads or those with poor visibility may be too dangerous to allow vehicles to pass.

According to most traffic laws, double yellow lines may only be crossed in order to make a turn. Double yellow lines may not be crossed in order to pass cars. Likewise, the time of day does not change when or how the rules that these lines represent may be followed.