O'ahu can be circled except for the roadless west-shore area around Ka'ena Point. Elsewhere, major highways follow the shoreline and traverse the island at two points. Rush-hour traffic (6:30 to 8:30 AM and 3:30 to 6 PM) can be frustrating around Honolulu and the outlying areas, as many thoroughfares allow no left turns due to contra-flow lanes. Parking along many streets is curtailed during these times, and towing is strictly practiced. Read curbside parking signs before leaving your vehicle, even at a meter.
Asking for directions will almost always produce a helpful explanation from the locals, but you should be prepared for an island term or two. Instead of using compass directions, remember that Hawai'i residents refer to places as being either mauka (toward the mountains) or makai (toward the ocean) from one another. Other directions depend on your location: in Honolulu, for example, people say to "go diamondhead," which means toward that famous landmark, or to "go 'ewa," meaning in the opposite direction. A shop on the mauka-Diamond Head corner of a street is on the mountain side of the street on the corner closest to Diamond Head. It all makes perfect sense once you get the lay of the land.
You can pretty much count on having to pay more at the pump for gasoline on O'ahu than on the U.S. mainland.
O'ahu is a relatively easy island to navigate. Roads and streets, although they may challenge the visitor's tongue, are well marked; just watch out for the many one-way streets in Waikiki. Keep an eye open for the Hawai'i Visitors and Convention Bureau's red-caped King Kamehameha signs, which mark major attractions and scenic spots. Ask for a map at the car-rental counter. Free publications containing good-quality road maps can be found at most hotels and resorts and throughout Waiki[i]ki.
Be sure to buckle up. Hawai'i has a strictly enforced seat-belt law for front-seat passengers. Children under four must be in a car seat (available from car-rental agencies). Children 18 and under, riding in the backseat, are also required by state law to use seat belts. The highway speed limit is usually 55 mph. In-town traffic moves from 25 to 40 mph. Jaywalking is very common, so be particularly watchful for pedestrians, especially in congested areas such as Waikiki. Unauthorized use of a parking space reserved for persons with disabilities can net you a $150 fine.
O'ahu's drivers are generally courteous, and you rarely hear a horn. People will slow down and let you into traffic with a wave of the hand. A friendly wave back is customary. If a driver sticks a hand out the window in a fist with the thumb and pinky sticking straight out, this is a good thing: it's the shaka, the Hawaiian symbol for "hang loose," and is often used to say "thanks," as well.