At last count there were almost 850,000 people living on Oahu and over 630,000 vehicles are jamming the highways in and around Honolulu. There are actually people who live just 15 miles away from Honolulu in the bedroom community of Kailua who are forced to leave for work well before 6 a.m. every morning so they can avoid traffic jams that go on for miles. Some even finish their sleep in their parked cars once they get to work.
Of course the traffic congestion problems are accentuated by the influx of tourists that descend on Honolulu through-out the year. More tourists means more taxis, tour buses, and rental cars that add to the already over-crowded highway system. Basically, there is one main highway that travels the length of Honolulu. There is virtually no other road that can be used to get in and out of downtown Honolulu.
As farmlands became increasingly mechanized over the years, more and more residents of the Island began to seek work in Honolulu. At the same time commercial airlines made traveling to the island easier and as a result the population of Oahu continued to climb. That means the main highway going in and out of Honolulu is extremely crowded with commuters, trucks and full buses during the morning and evening rush hours. Plans are being considered to build a rail system in Honolulu that would link the airport, Pearl Harbor, the University of Hawaii's campus, the bus terminal, and the Ala Moana shopping center. This would take much of the strain off the road system. There is really no way to widen the main highway that runs through Honolulu because the island is so narrow and is bordered by expensive properties. There is simply no space available to turn two lanes into four or it would have been done years ago.
Whenever possible, visitors to Honolulu would be well advised to avoid being on the main highway during the busier times of the day. To avoid the frustration of sitting in a cramped, hot vehicle when traffic is slow-moving, it might be wiser to take an air-conditioned city bus. Also it would be wise to plan carefully when choosing a hotel for your stay in Honolulu. For instance there are several hotels that are right on the beach and also within walking distance of the Ala Moana shopping center, one of the biggest malls in the country. With careful planning, there will be little need to spend time fighting the traffic day after day.
However if you do happen to be driving a rental car, it should be noted that for the most part local drivers are courteous. Certainly there is some tail-gating that goes on, but at the same time even if traffic is bumper-to-bumper local drivers will let you in if they see you signaling to change lanes. The smartest thing visitors from the mainland can do is leave their mainland driving habits at home and drive with courtesy and patience while visiting Honolulu.