I would avoid using salt/vinegar in solution to kill weeds. The acid in vinegar can cause a battery effect, and salt in solution is very conductive. Both of these can interfere with normal crossing protection by keeping the detection relay from being able to close or open properly. The battery effect can keep the relay closed when the approach circuit is occupied, and the conductivity of saline solution can cause the relay to drop (a virtual shunt)when there is nothing occupying the approach. If there is grade crossing predictor technolgy involved, all kinds of wacky responses can happen. In places where there is no track circuitry, this might be OK, but where used over long time periods there might might be enough salt/vinegar accumulation to contaminate soil into becoming conductive. Railroads that carry large volumes of coal can experience similar problems due to sulfur in the coal dust combining with moisture and becoming acidic.