Road bridges generally cross bodies of water, or low lying areas along the road network.
Bridges are often evident by the thinning of the road where the bridge begins and the corridor either side of the road disappears.
In Figure 2.2.4.3a the shadows cast by the bridge is evident
Figure 2.2.4.3b shows the difficulty of bridge capture solely from SPOT imagery.
GA advise that bridge capture when only SPOT imagery is available, should only be attempted with the aid of Reference Material or when certainty is high. The highlighted 'Uncertain bridge' should not be captured from imagery alone, it appears that the road may cross a watercourse but the method of crossing is uncertain, i.e. bridge, culvert or ford.
Regional Considerations:
Figure: 2.2.4.3 Representation of Road Bridge Lines.
