SALEM (AP) — Oil prices may be affecting not just the gas you put in your car, but the roads you drive on as well. Oil topping $135 per barrel is driving up the price of asphalt, which is oil-based.

The costs are already affecting some projects in Oregon, the Salem Statesman Journal reports.

Salem will put off work planned on six streets this summer because of recent price increases, said Mark Becktel, the city’s transportation services manager. The asphalt involved would have cost about $22,000 at current prices.

A year ago, the going rate for hot mixed asphalt was $44 per ton. But the cost to the city now is about $50 per ton, and next month, it will be $56 per ton.

A combination of higher prices for asphalt, fuel and steel will also eat into the 2008 construction budget of the Oregon Department of Transportation, although the exact amount is unknown.

ODOT contracts contain cost-escalation clauses, which are intended to compensate contractors for increases in the three materials between when a project is bid by a contractor and when it is finished. Because bidding is staggered, estimates are hard to come by.

Asphalt remains the preferred material for paving and patching city streets, although concrete is used on some stretches of state highways because it bears more weight.

But the oil byproduct used to make asphalt may grow scarcer as refineries use more efficient technologies to squeeze higher-value products out of every barrel.