Escalating costs of asphalt and concrete have threatened to slow or scale back transportation construction projects in the Phoenix area recently, but have not impacted projects in Yuma County, according to several officials.

Lucy Shipp, Arizona Department of Transportation spokeswoman in Yuma, said the price of raw materials affects how various state contractors are able to place their bids.

"Costs were going up but then they leveled off and now are coming down just a little bit," Shipp said.

She explained that every transportation project is open for bids and ADOT always accepts the lowest and best bid. Shipp defined the "best" bid as one coming from a contractor who can complete the work by the scheduled deadline and who has materials to meet the project's requirements.

Larry Brown of Abacus Project Management Inc. assists contractors with bid estimates and is helping with building construction and parking lot expansion at Arizona Western College in Yuma. Brown said rising costs have hit California worse than Arizona but that they are bound to make a local impact soon.

"It's really a man-made shortage," Brown said. "Refiners came up with better techniques for crude oil, which is used in the making of 'hot mix,' used to make asphalt paving ... but now it's also used for diesel fuel."

He said that he is not aware of any slowing in construction projects locally.

Brown said that because new technology can mean more uses for a material, demand increases and that raises prices. And he said highway projects are impacted more than buildings because more raw materials are required. He also said concrete shortages are affected by world markets, especially the current building boom in India and China.

Bill Smith, Director of Facilities Management and Planning at Arizona Western College is overseeing 202,000 square feet of construction at the school's main campus.

Smith said he noticed a dramatic rise in building materials after Hurricane Katrina struck the Gulf Coast in 2005 but had not seen any significant change in the past year.

Maricopa County Transportation officials said road widening and new arterial streets are affected by high costs and they face a $110 million shortfall. According to the Maricopa Association of Governments, one of the reasons for spiraling costs is a shortage of road-building materials.

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William Roller can be reached at wroller@yumasun.com or 539-6858.