City transportation officials have a lot of explaining to do.

Friday was the last day for the public to comment and raise concerns about the city's draft environmental impact statement for a planned $5.43 billion elevated commuter rail.

Now the city must go about responding to hundreds of comments and likely thousands of questions about the 20-mile East Kapolei-to-Ala Moana rail project as part of a lengthy environmental review. The environmental study is a major hurdle in the city's effort to obtain more than $1 billion in federal money to build the train system.

The city expects to complete the environmental review in time to begin construction in December. The city's timeline calls for service between West Loch and Waipahu to start in late 2013 and full service to Ala Moana by the end of 2018. That timetable assumes that the environmental impact review will go relatively smoothly. For that to happen, the city will need to adequately address a range of concerns about noise, aesthetics, archaeological conservation, energy consumption and more.

Common concerns raised by local residents and agencies include:

• Why build the project's first phase in East Kapolei rather than urban Honolulu?

• Whether the city adequately considered rail alternatives such as elevated managed highway lanes, bus rapid transit and an at-grade (ground-level) train system.

• Would it be better to have the train go directly to Waipi'o and Mililani or through Salt Lake?

• Should the current route be changed to avoid the Prince Kuhio Federal Building to address concerns about security and possible terrorist attacks?

• Are the city's cost projections accurate and what will the city do if it runs out of money before the project is finished?

• How will the city address concerns that the train will contribute to Honolulu's crime problems?

Other comments raise questions about the accuracy of the city's ridership predictions and traffic forecasts.

City officials already are grouping and categorizing concerns and preparing responses, which will be included in a final environmental impact statement, which they hope to release this summer.