 As a result, some road maintenance agencies have networks of ice prediction stations, to prevent unnecessary gritting which not only wastes salt, but can damage the environment and disrupt traffic.The U.S. state of Oregon uses magnesium chloride, a relatively cheap chemical similar in snow-melting effects to sodium chloride, but less reactive, while New Zealand uses calcium magnesium acetate, which avoids the environmentally harmful chloride ion altogether.Urea is sometimes used to grit suspension bridges, as it does not corrode iron or steel at all, but urea is less effective than salt, and can cost up to 7 times more weight-for-weight.