Short note: river crossing alternatives

When a road alignment meets a river, the following crossing alternatives are considered and chosen on traffic, river conditions and cost (IRC and NRS 2070).

1. Ford / drift - the road is taken through the river bed, with a stabilised (paved) section. Cheapest, but can be used only when the river is shallow, the flow is small and the traffic is light; closed during floods.
2. Causeway / Irish bridge (submersible bridge) - a road across the stream with pipes or vents, overtopped in floods. Suitable for seasonal, flashy rivers and low traffic.
3. Culvert / small bridge - for small streams; the cheapest permanent crossing for small flows.
4. Major bridge - slab, girder, truss, arch, cable-stayed or suspension, for all-weather crossing of wide, deep or perennial rivers. High cost.
5. Ferry or ropeway/ suspension footbridge - for very low traffic, temporary or in remote areas (where road cost is not justified).
6. Realignment to a better site - move the crossing to the best site of the river: narrow, straight, stable banks, rock foundation, right angle crossing.

Selection criteria

• Traffic volume and type, and the importance of the road
• Width, depth, discharge and flood characteristics
• Bank stability, foundation conditions
• Cost of construction and maintenance and the delay or interruption from floods
• Skew (best at right angle to the flow), approach roads and bridge length
• Environmental effects