Monthly tax collections needed to pay for Honolulu's planned $5.4 billion elevated commuter train fell 11 percent last month to $12 million compared with April 2008. The decline reflects a reduction in economic activity relating to a statewide slump.

Through the first 10 months of the current fiscal year, the half-percentage-point general excise tax surcharge raised a net $119.7 million for the city, based on figures provided by the state Department of Taxation. That's down 14 percent, or $19 million from year-ago levels.

With two months remaining in the current fiscal year, tax collections remain well below the pace needed to meet a city forecast of $188 million in tax surcharge revenues.

City officials hope to use the tax to raise nearly $4.1 billion, on an inflation-adjusted basis, from 2007 through 2022 to pay for the 20-mile rail system linking East Kapolei to Ala Moana. That, coupled with about $1.4 billion in anticipated federal money, is expected to pay the estimated $5.4 billion in capital costs associated with rail, according to the city's financial plan.

If monthly tax collections continue at the current average of $13.2 million, the city could be short about $42 million in transit funds by June 30. In the fiscal year starting July 1, the city's financial forecast anticipates transit tax revenue growing to an inflation-adjusted $198 million, or $16.5 million a month.

The state began collecting a half-percentage point general excise tax surcharge for transit in January 2007. The tax is scheduled to expire at the end of 2022. Overall, the tax has raised $349.3 million during the first 28 months. That figure, and all figures in this article, do not include the 10 percent the state takes off the top to pay for administering the tax.

Officials want to begin construction in December, contingent on federal approval, and launch service in phases between late 2013 and 2019.