Numerous travel upsets have been recorded. When the mobile hydraulic crane upsets on the left side where the operator's cab is located, the lightweight sheet metal cab is easily crushed, usually trapping the operator before escape is possible. Crawler tractors can remain stable up to a 57 degree side slope. Mobile hydraulic cranes, however, are rarely stable on side slopes beyond 35 degrees. Because of their versatility with four-wheel drive and four-wheel steer, rough- terraincranes do encounter slopes of over 35 degrees that could cause upset.