Discussion about tracks brought back my experience when I road over cattle guard on road/driveway to service station/store cattle guards are (4 inch wide paralell strips of bouncy metal above/across dugout road surface aout a foot deep about 12feet by 7feet). I almost always walk bike across them, but this time I road over it. I got halfway across cattle guard and lost controle of my bike because of the bouncing metal strips. While I was falling I felt my leg slip between the metal strips, my foot hit the bottom (12 inches down) while I was falling on the way/hitting the ground I said to myself "I have broken my leg". Somehow I dd not break my leg and was not seriously hurt. BE VERY CAREFUL CROSSING CATTLE GUARDS!