DES MOINES (AP) -- The Iowa Department of Transportation's plan to spend $4 billion over the next 20 years on highways is too narrowly focused and doesn't address environmental issues and alternative forms of transportation, critics say.

Iowa's plan only raises money to build and repair roads, and not enough money to for public transportation, railroads, walking and biking trails, aviation or other options.

With experts' warnings to reduce greenhouse emissions and a call for tougher mileage requirements on automobiles, the state's plan is a step backward, critics said.

"It's unfortunate that we are designating transportation funds to meet the needs of the past," said Stephanie Weisenbach, program coordinator for 1000 Friends of Iowa, a citizens' group that promotes sustainable development and responsible land use.

Mark Kresowik, a conservation organizer for the Sierra Club in Iowa, said not increasing alternatives to cars and trucks "would be a fairly big mistake, just given the interest we are seeing in reducing greenhouse gas emissions."

A subcommittee of the Iowa Climate Change Advisory Council is working on transportation and land use issues, and former state transportation commission member Thomas Hart, of Davenport, was hired to look at the impact the state's changing economy will have its transportation system.

Transportation department Director Nancy Richardson said the agency has worked to help other types of transportation, such as railroads, public transit, as well as pedestrians and bicycles.

The agency's plan, dubbed the TIME-21 plan, addresses a lack of money to maintain the state's road network, Richardson said.

Lawmakers have rejected an increase in the state's gasoline tax to fund the TIME-21 program, but are exploring possible increases in driver's license and car license fees.

Richardson said the state has secured $2 million a year to help build or improve railroad freight facilities; spends about $11 million assist 35 public transit systems statewide; and has worked to improve services for bicyclists, airport users and other transportation modes.

Supporters of transportation alternatives say that's not enough.

Brad Miller, general manager of the Des Moines Area Regional Transit Authority, wants lawmakers to make bus service a higher priority.

While ridership is up 8 percent over the past six months, the service is struggling because it lacks money for newer buses, Miller said.

"When we look at transportation investment for the future of Iowa, we need to not just look at roads and bridges," Miller said.

Bicycle riders want more, too.

"The important part is that when roads are rebuilt or new roads are constructed, that they consider pedestrians and cyclists," said Angela Dalton, director of the Bike to Work program in the Des Moines area.

Sen. Tom Rielly, D-Oskaloosa, said lawmakers are open to hearing critics' complaints.

"They make a very valid point that we need to think beyond traditional ways," Rielly said. "But while we are doing that, we can't ignore our existing needs" to fix road and bridge