The City needs to finish the project as planned. Yes, it is expensive and yes, there will be significant traffic impacts during construction.  However, in the long run the benefits from the project will significantly outweigh the costs.  The Honolulu TOD Study Scenarios Report (Calthorpe, 2013) found the rail project and transit-oriented development (TOD) will create $20-27 billion in benefits to Honolulu by 2050.  Even higher benefits canned be achieved through additional policies that lead to higher ridership such as congestion pricing. 
These kinds of large infrastructure projects are what built America and, in particular, are what help make American cities economically viable.  Over the last few decades Americans have become increasingly averse to investing in high quality infrastructure projects like these and America has started falling behind the rest of the world.