SAN ANTONIO (AP) - Drivers on two West Texas highways could soon be able to go 80 mph without risking a speeding ticket. A proposal by the state Department of Transportation seeks to raise the speed limit on Interstates 10 and 20 in West Texas, despite opposition from fuel conservation advocates. The Texas Transportation Commission could take up the proposal next week. Legislation passed last year allows for higher speeds in 10 West Texas counties, most of which currently have 75 mph speed limits. Carlos Lopez, director of traffic operations for the transportation department, said a survey of both interstates found that 85 percent of motorists already were driving up to 79 mph. ``If people begin to think that the number on the sign is unreasonable, then they won't respect it,'' Lopez said. ``Just putting up a lower number on the highway isn't going to slow down traffic.'' But with gas prices at a premium, some groups said drivers should be encouraged to slow down rather than speed up. Increasing the speed limit ``will have a perverse reaction,'' said Peter Iwanowicz, director of environmental health at the American Lung Association. ``Increasing the speed limit will increase fuel use.'' U.S. Department of Energy studies show gas mileage usually decreases rapidly at speeds above 60 mph. Transportation department spokesman Randall Dillard said the 80 mph speed limit was also intended to make the interstate safer, because motorists would be traveling at a uniform speed.