Ridership estimates for Honolulu's planned $5.5 billion commuter train have increased despite declining estimated population growth on Oahu.

The projection for average weekday boardings in 2030 for the new rail line has risen from 95,000 in the city's November 2008 draft environmental impact statement to 116,300 in the city's final EIS, released last month.

The League of Women Voters of Hawaii and Honolulutraffic.com, a group opposed to rail, have questioned the accuracy of the city's ridership projections, pointing to declining population estimates and uncertainty about a planned 11,750-house development in East Kapolei along the rail line.

If ridership is less than anticipated, added public funds may be needed to subsidize the elevated commuter rail operations, and there could be less interest in developing real estate along the 20-mile route.

When asked in an e-mail whether the city plans to update its population assumptions to reflect the lower forecast, Toru Hamayasu, deputy director of the Honolulu Department of Transportation Services, wrote, "The FEIS (final EIS), as did the DEIS (draft EIS), uses the socio-economic data that was available from OahuMPO" (Metropolitan Planning Organization), at the time that the EIS work began, based on DBEDT's "Population and Economic Projections for the State of Hawaii to 2030," prepared in August 2004.

Hamayasu said ridership estimates rose in the final EIS based on updated Oahu air passenger and commuter travel mode forecasts and other socioeconomic data. Other information such as rising job forecasts also support the increase in ridership estimates, Hamayasu said.

"While the most recent DBEDT forecasts have lower population projected than the August 2004 forecasts, the most recent 2030 employment forecast for Oahu is higher than the August 2004 forecast," he wrote. "Thus using the latest forecast, with the higher employment, would likely result in more work trips which are attractively served by transit."

Critics of the city's rail ridership projections also contend that the estimates are based on the successful completion of a new housing development in East Kapolei that is now in doubt. D.R. Horton-Schuler Homes' Hoopili development might not be built as originally planned, and that could reduce rail ridership. The 11,750 homes were supposed to be built near two train stations.

The state Land Use Commission ruled last year that the developer did not comply with state law requiring that development be substantially completed within a 10-year period. Hoopili is slated to be built over 20 years. The decision has indefinitely delayed the project.

"The effect on transit ridership of not building Hoopili will depend on where the population and employment planned for Hoopili locates instead," said Hamayasu. "If the population and employment otherwise expected in Hoopili locates within the rail corridor, it is likely that rail will be used for many trips the same as if Hoopili were developed."