The temporary S-curve installed on the Bay Bridge over Labor Day weekend is causing accidents and slowing down traffic. A big rig overturned on the bridge yesterday, snarling traffic for hours, when the driver tried to negotiate the elongated curve at too high a speed. According to the Chron, CalTrans plans to erect signs warning motorists to reduce their speed before the S-curve in an attempt to curtail crashes. But the move also will further slow down commute traffic. The curve will be in place until at least 2013 as crews complete work on a new eastern span of the bridge.