Harbourside Transportation Consultants completed the design of the vertical and horizontal alignments, from initial concept layouts through to detailed design and tender for the new approaches to the Rocky Barachois Bridge Replacement.

Investigation of the approaches at this site indicated that constructing the new bridge beside the existing, while maintaining two lanes of traffic on the existing bridge required significant infilling and rework of the approaches. Options considered the use of a two lane detour structure positioned either east or west of the existing alignment to allow the new bridge construction along the existing alignment.

This investigation indicated that less fills would be required with the detour structure positioned east of the existing bridge. Based on this, three highway horizontal alignments were considered: matching the existing, shifting the alignment east (7,045 mm offset) so that it partially overlapped the existing structure, and shifting the alignment east to be clear of the existing structure. Constructing the new bridge partially in the footprint of the existing bridge helps to minimize the amount of infilling on the approaches. Different phasing/detour options were considered in order to maintain two lanes of traffic throughout construction.

For completeness and in the interest of reducing the overall project cost, an option was developed which maintained a single alternating lane of traffic throughout construction. The third highway alignment option considered the new bridge constructed adjacent to the existing bridge with a minimum of 900 mm clearance between the new and existing structures. This option presented the simplest option from a construction phasing perspective as well as removes the demolition of the existing structure from the critical path.

The vertical alignment options were investigated for each bridge structure alternative to satisfy the minimum Stopping Sight Distance requirements of TAC and to maintain a clearance box similar to the existing. The current minimum clearance box is approximately 4,200 mm. The vertical alignments considered resulted in a minor clearance box reduction. The vertical alignment was also optimized to minimize the construction zone length and the overall construction costs.

All alignment work was carried out using appropriate TAC and NLDTW Guidelines and sound engineering design practices. The design minimized the amount of realignment required for the existing highway while providing the highest level of safety and driver comfort as practically possible.