The Dumbarton Rail Bridge carries a single railroad track on six 180-foot (55 m) Pratt through truss spans and a central 310-foot (94 m) swing Petit through truss span, for a total steel bridge length of 1,390 feet (420 m).
The steel structure is symmetric, with three truss spans flanking each side of the central swing span.
Each 180-foot (55 m) truss span weighs approximately 470 to 480 short tons (430 to 440 t).
The six truss spans were constructed on shore and floated into place using a converted freight car boat, the Thoroughfare.
The swing span weighs approximately 1,215 to 1,500 short tons (1,102 to 1,361 t).
When the swing span is open to accommodate water traffic, it affords a 125-foot (38 m) wide navigation channel to either side.
The eastern trestle approach is 1,002 feet (305 m) long, and the western trestle approach was 5,366 feet (1,636 m) long.

The steel structure was designed to accommodate a double-track line.
Both eastern and western trestle approaches were designed and built with single track service, as they were completed prior to the decision to accommodate double-track service on the steel structure.
The swing span was completed with double-track lines.

The bridge was designed to accommodate automobile or horse traffic on an overhead platform.
A proposal for an upper-deck road was advanced in 1907, prior to the completion of the bridge, but was dismissed as unlikely just a few months later.

The Cut-off reduces the distance (by rail) between Oakland and San Francisco by 26.1 miles (42.0 km).

The depth of the Bay at the middle of the channel was 50 feet (15 m) at mean low tide, with a mean high tide variance of 6 feet (1.8 m).
Preliminary test piles had shown the mud was 2 to 4 feet (0.61 to 1.22 m) deep in the middle of the channel and 16 to 18 feet (4.9 to 5.5 m) deep at the shoreline, atop a layer of sand and gravel ranging from 15 to 20 feet (4.6 to 6.1 m) deep.
Each truss span rests on two cylindrical concrete piers 18 feet (5.5 m) in diameter at either end, except where the truss spans meet the swing span.
The truss-swing span interface is supported on four cylindrical concrete piers 18 feet (5.5 m) in diameter.
The swing span's center is supported by a 40-foot (12 m) diameter cylindrical concrete pier resting atop more than one hundred piles.

The original bridge design for the San Francisco Bay span called for trestle approaches all the way to the swing span.
On 21 August 1907, the supports for a 120-foot (37 m) section of eastern approach trestle, which had been built to within 120 feet (37 m) of the swing span, washed out in the receding tide and the bridge plans were modified.
The first proposed change was to modify the trestle approaches 200 feet (61 m) immediately to the east and 600 feet (180 m) immediately to the west of the swing span by changing these to double-track width.
However, the wider trestle bents continued to vibrate in the receding tide.
The final as-built design eliminated approximately 1,080 feet (330 m) of trestle approaches in favor of the six 180-foot (55 m) steel truss spans, three on either side of the swing span.

The swing span across Newark Slough is similar to the Dumbarton Rail Bridge swing span; both are through truss swing spans, both are sized for double-track service, and both have the mechanical/Operator's house atop the center of the truss.
The Newark Slough bridge is 182 feet (55 m) long and is a Baltimore truss design.
The single-track timber trestle approaches to the Newark Slough swing span are built all the way to the swing span rest piers, and so the as-built Newark Slough span is presumably similar to the original design of the Dumbarton Rail Bridge, prior to the 1907 redesign incorporating flanking trusses.

When the Dumbarton Rail Bridge was in use, boaters would signal the operator, who would start a diesel engine and rotate the bridge to the open position on a large gear.
The bridge could swing open or closed in two minutes.
The bridge has since been welded into the open position.
The Dumbarton Rail Bridge carries a single railroad track on six 180-foot (55 m) Pratt through truss spans and a central 310-foot (94 m) swing Petit through truss span, for a total steel bridge length of 1,390 feet (420 m). The steel structure is symmetric, with three truss spans flanking each side of the central swing span. Each 180-foot (55 m) truss span weighs approximately 470 to 480 short tons (430 to 440 t). The six truss spans were constructed on shore and floated into place using a converted freight car boat, the Thoroughfare. The swing span weighs approximately 1,215 to 1,500 short tons (1,102 to 1,361 t). When the swing span is open to accommodate water traffic, it affords a 125-foot (38 m) wide navigation channel to either side. The eastern trestle approach is 1,002 feet (305 m) long, and the western trestle approach was 5,366 feet (1,636 m) long.
The steel structure was designed to accommodate a double-track line. Both eastern and western trestle approaches were designed and built with single track service, as they were completed prior to the decision to accommodate double-track service on the steel structure. The swing span was completed with double-track lines.
The bridge was designed to accommodate automobile or horse traffic on an overhead platform. A proposal for an upper-deck road was advanced in 1907, prior to the completion of the bridge, but was dismissed as unlikely just a few months later.
The Cut-off reduces the distance (by rail) between Oakland and San Francisco by 26.1 miles (42.0 km).
The depth of the Bay at the middle of the channel was 50 feet (15 m) at mean low tide, with a mean high tide variance of 6 feet (1.8 m). Preliminary test piles had shown the mud was 2 to 4 feet (0.61 to 1.22 m) deep in the middle of the channel and 16 to 18 feet (4.9 to 5.5 m) deep at the shoreline, atop a layer of sand and gravel ranging from 15 to 20 feet (4.6 to 6.1 m) deep. Each truss span rests on two cylindrical concrete piers 18 feet (5.5 m) in diameter at either end, except where the truss spans meet the swing span. The truss-swing span interface is supported on four cylindrical concrete piers 18 feet (5.5 m) in diameter. The swing span's center is supported by a 40-foot (12 m) diameter cylindrical concrete pier resting atop more than one hundred piles.
The original bridge design for the San Francisco Bay span called for trestle approaches all the way to the swing span. On 21 August 1907, the supports for a 120-foot (37 m) section of eastern approach trestle, which had been built to within 120 feet (37 m) of the swing span, washed out in the receding tide and the bridge plans were modified. The first proposed change was to modify the trestle approaches 200 feet (61 m) immediately to the east and 600 feet (180 m) immediately to the west of the swing span by changing these to double-track width. However, the wider trestle bents continued to vibrate in the receding tide. The final as-built design eliminated approximately 1,080 feet (330 m) of trestle approaches in favor of the six 180-foot (55 m) steel truss spans, three on either side of the swing span.
The swing span across Newark Slough is similar to the Dumbarton Rail Bridge swing span; both are through truss swing spans, both are sized for double-track service, and both have the mechanical/Operator's house atop the center of the truss. The Newark Slough bridge is 182 feet (55 m) long and is a Baltimore truss design. The single-track timber trestle approaches to the Newark Slough swing span are built all the way to the swing span rest piers, and so the as-built Newark Slough span is presumably similar to the original design of the Dumbarton Rail Bridge, prior to the 1907 redesign incorporating flanking trusses.
When the Dumbarton Rail Bridge was in use, boaters would signal the operator, who would start a diesel engine and rotate the bridge to the open position on a large gear. The bridge could swing open or closed in two minutes. The bridge has since been welded into the open position.
Dumbarton Rail Bridge