You said "when driving conditions are poor. Do you mean fog, rain, snow, darkness or other? This can clue you in to the specific problem.
Check advance warning signs. Add chevrons or delineators if needed. Is advisory speed correct? Are all signs in good condition, properly placed and retroreflective at night?
Check superelevation of road and correct if needed. Check pavement for polished aggregate or bleeding asphalt.
Salt wash? Do you mean problems occurr during ice & snow?
Calibrate spreaders on snow plows to better control amount of salt used. If crop damage is severe, investigate using acetates (CMA) rather than chlorides. Sand won't help - it's mixed w/ 10% salt to keep it from freezing, and you need almost 10 times as much. Also, the sand wash will clog drainage and affect soil, too.