1. Introduction
Depending on the purpose, a bridge can be planned in various shapes. To enable a large amount of transportation, a bridge designer can apply several design considerations to a bridge design. Let’s look at one of them.
A double-layer bridge provides more space through the double-layer girder to transport vehicles, trains, or pedestrians. This type of girder has enough vertical clearance to carry them. Therefore, it could make clearance issues under the bridge, and also it could make aero stability issues. Nevertheless, the double-layer girder can be one of the available options for a bridge in areas where heavy traffic is expected.
The following post would like to introduce some special bridges with cable supports and double-layer truss girders that can carry heavy pedestrian and vehicle traffic. The table below shows a list of some of these special bridges.
| Built Date | Bridge Name | Bridge Type | Main Span Length (m) | Carriageway no. |
| 1931 | George Washington Bridge | Suspension Bridge | 1,067.0 | 8 + 6 lanes |
| 1959 | Fort Pitt Bridge | Bowstring Arch | 228.6 | 4 + 4 lanes |
| 1962 | Sherman Minton Bridge | Bowstring Arch | 240.0 | 3 + 3 lanes |
| 1964 | Verrazzano-Narrows Bridge | Suspension Bridge | 1298.45 | 6 + 6 lanes |
| 1985 | Onaruto Bridge | Suspension Bridge | 876.0 | 4 + 2 lanes |
| 1993 | Rainbow Bridge | Suspension Bridge | 570.0 | 4 + 4 lanes |
| 2002 | Gwangan Bridge | Suspension Bridge | 500.0 | 4 + 4 lanes |
| 2011 | Gogeum Bridge | Cable-Stayed Bridge | 480.0 | 2 +1 lanes |
2. Bridge Details
2.1 George Washington Bridge
The George Washington Bridge is a suspension bridge built in 1931 in the USA. The total length of the bridge is 1,450m, and the main span is 1,067m. Pylons and girders in the bridge consist of truss structures. The girder has two levels, and it carries vehicle traffic only. The total lanes are 14 lanes. The upper level has eight lanes, and the lower level has six lanes. Each level has been planned as two-way traffic.
Figure 1. George Washington Bridge
2.2 Fort Pitt Bridge
The Fort Pitt Bridge is a bowstring arch bridge built in 1959 in the USA. The total length of the bridge is 368m, and the main span is 230m approximately. Each level has four lanes, and it has been planned as one-way traffic.
Figure 2. Fort Pitt Bridge
2.3 Sherman Minton Bridge
The Sherman Minton Bridge is a twin bowstring arch bridge built in 1962 in the USA. The total length of the bridge is 625.7m, and the main span is 240m approximately. Each level has three lanes, and it also has been planned as one-way traffic.
Figure 3. Sherman Minton Bridge
2.4 Verrazzano Narrows Bridge
The Verrazzano Narrows Bridge is a suspension bridge built in 1964 in the USA. The bridge's total length is 4,176m, and the main span is 1,298m long approximately. This bridge has a great span length among bridges that have multi-layer girders. Each level has six lanes, and it also has been planned as two-way traffic.
Figure 4. Verrazzano Narrows Bridge
2.5 Onaruto Bridge
The Onaruto Bridge is a suspension bridge built in 1985 in Japan. The total length of the bridge is 1,629m, and the main span is 876m. The upper level has four lanes, and it has been planned as two-way traffic. The lower level has two lanes. It has been planned for train traffic initially. However, both levels are used for pedestrians at the moment.
Figure 5. Onaruto Bridge
2.6 Rainbow Bridge
The Rainbow Bridge is a suspension bridge built in 1993 in Japan. The total length of the bridge is 798m, and the main span is 570m. Each level has four lanes, and it has planned as two-way traffic. The upper level allows vehicles only. So, pedestrians can pass through the lower level.
Figure 6. Rainbow Bridge
2.7 Gwangan Bridge
The Gwangan Bridge is a suspension bridge built in 2002 in Korea. The total length of the bridge is 900m, and the main span is 500m. Each level has four lanes, and it has planned as one-way traffic.
Figure 7. Gwangan Bridge
2.8 Gogeum Bridge
The Gogeum Bridge is a cable-stayed bridge built in 2011 in Korea. The total length of the bridge is 1,116m, and the main span is 480m. Each level of girder in the bridge has a different purpose. The upper level has two lanes, and it has planned as two-way traffic. The lower level has one lane, and it is used for pedestrian traffic.
Figure 8. Gogeum Bridge
