State and county transportation agencies are preparing road surfaces as sub-freezing temperatures close in on the area. A spokeswoman for the Texas Department of Transportation says TxDOT trucks are treating state highways with salt water to melt ice. She says their crews start days in advance of freezing weather and continue to treat the road surface as needed. The Bexar County Public Works Department is treating roads with chat rock, a gravel-like substance that doesn't melt ice but provides traction. Officials are warning residents to stay off the roads this weekend if at all possible.