 The two swing bridges and their timber trestle approaches were known to be in poor shape since 1996, and a subsequent 2008 engineering investigation found the concrete foundations were also degraded, possibly since they were constructed in 1910.The 2003 "Project Study Report" proposed replacement of the Dumbarton Rail Bridge swing span with a bascule, replacement of the Newark Slough Bridge with a steel girder swing span, and new concrete trestles.The existing two-track Dumbarton Cut-off line would be converted to a single track system with centralized traffic control; the second track would be retained as a siding in certain portions.