Traffic is horrible in Honolulu. Be prepared to sit in traffic to get anywhere. This includes getting to the airport, so yourself plenty of time to get there (not that you'd be too upset to miss your flight - who wants to leave Hawaii? :)
Traffic can get very heavy, and down right ridiculous at times. Listen to the Traffic report with Danielle Tucker before you head out ... she'll tell you what highways are flowing smoothly, and where to avoid due to accidents or other traffic issues. (My station is KGMZ 107.9FM) Heaviest traffic hours are 6:30am - 9:00am and from 2:30pm - 7pm anywhere in the downtown area.
Traffic! Traffic! Traffic! If you are driving around on Oahu, you WILL encounter: bumper to bumper cars; tourists unfamiliar with the area making quick lane changes or strange turns; crowded parking lots; LOTS of pedestrians; and road construction. Stay alert and don't be in a hurry. Remeber, you are not on the mainland. And drive with Aloha.....if someone needs in your lane, let them in. If someone looks confused, give them space. And a smile and a wave are always welcome there. Enjoy your trip SAFELY!