Some situations should be confronted with extreme caution. Railroad tracks can bite you hard when they are wet. The standard advice is to try to cross railroad or other metal tracks at a right angle, even in the dry. When they are wet, this is imperative. Otherwise, you risk having the tire slip into the groove alongside the track, which will immediately ruin your whole day. Other large metal road surfaces or metal sections running parallel to your direction of travel -- some expansion joints, for example -- are equally hazardous and should be approached cautiously and upright. A thin strip of metal can usually be crossed while leaned over mildly; tires slip then catch again after crossing. However, a large metal surface such as a bridge grate, a manhole cover or a cattle guard, may permit the tire to slip too much to recover traction. Painted surfaces can be almost as slippery as metal.