The web site HonoluluTraffic.com has a very useful and informative aerial tour of the "light" rail line envisioned for O'ahu. The tour traces the proposed rail line, which will be elevated, following the topography of the land.
Interestingly, the current plan is to start the rail line in the undeveloped western reaches of the southern part of O'ahu (where the video tour starts) and end on the western fringe of the downtown. In essence, the rail line misses the most dense and urban parts of the city. The rationale was that the rights of way could be secured more easily in the undeveloped western parts. But the need is in the eastern portions that is already heavily developed. The plan doesn't make much sense.
On the surface, Honolulu should be an ideal candidate for rail transit. It's a long, narrow strip of some of the densest urban stretches in the U.S. I thought so, too until I visited the city and island last May. A tour along the route and crash course on urban development and land-use patterns convinced me that rail transit would be far less effective than HOT lanes and express bus services in meeting the island's mobility needs.