DES MOINES -- Iowa Department of Transportation officials Wednesday said the shortfall in revenue required to meet the state"s critical highway and bridge construction needs has grown to $267 million annually.

That"s up from the $200 million yearly shortfall identified by DOT officials two years ago, according to a report the department prepared for state lawmakers.

The revised projections are likely to renew the debate over raising the state"s gasoline tax when the 83rd General Assembly convenes Jan. 12. Gov. Chet Culver has resisted such a move during the nation"s economic recession, but support has grown among some lawmakers who see it as the most viable option to keep pace with rising costs and deteriorating road conditions.

In the report, state transportation experts said their latest evaluation indicates the gap between transportation needs and revenue has been exacerbated by the worsening condition of Iowa"s roadway system, insufficient investment, construction cost escalation and the impacts of severe weather.

Based on current projections, yearly average revenue flowing into the road-use tax fund that is available to state, county and city jurisdictions grew slightly to $1.989 billion while the cost of meeting the most critical pavement and bridge preservation for interstate, primary and local roadways increased to $2.256 billion since the 2006 study.

DOT officials noted that legislation approved during the 2008 session to generate up to $115.3 million by fiscal 2012 through various transportation-related fee increases fell $84.7 million short of the target and the new projections boost that figure to $151.7 million.

"With the updated TIME-21 critical need funding level, the cumulative shortfall in funding also increases to the point that by fiscal 2012 it is over $820 million and by fiscal 2018 the cumulative shortfall is about $1.5 billion.

In their report findings, DOT officials note that out-of-state drivers are not paying a proportional share of road-use tax fund revenue generated by state fuel taxes and commercial truck registration fees compared to the number of vehicle miles traveled on Iowa"s public roadways.

"Additional funding mechanisms not currently utilitized in Iowa that could generate revenue from out-of-state drivers include severance tax on ethanol, sales tax on fuel, tolling, and a per-mile tax," according to the DOT report findings.

The report lists a number of options that could be used to generate additional transportation revenue -- noting that each one cent increase in the state"s gasoline tax generates $21 million, each one cent increase in the state"s diesel fuel tax generates $6.5 million and repealing the ethanol tax credit would equal $6 million per year.