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A419 COMMONHEAD JUNCTION IMPROVEMENT
A419 COMMONHEAD JUNCTION IMPROVEMENT
9. CONCLUSIONS AND RECOMMENDATIONS
9.1 Three options to solve the congestion and accident problems at Commonhead junction have been considered as follows:
- Option A - Overpass
- Option B - Underpass
- Option C - At-grade throughabout
9.2 The at-grade throughabout was rejected because it would not provide long term capacity, only around 6 years.
9.3 The 'overpass' and 'underpass' options would provide both adequate capacity and reduce the number of accidents.
9.4 Effects on groundwater, noise and visual effects are the main environmental impacts of the 'underpass' and 'overpass' options. The noise levels with the 'overpass' option, including mitigation would decrease or stay the same apart from three properties. Of the 434 properties assessed only 3 would experience a noise level increase. With the 'underpass' option there would be minimal noise increases at 97 properties but generally noise levels would decrease overall.
9.5 In terms of visual effects, the 'overpass' option would have moderate adverse visual impact for views across the AONB and winter views from Liden. However, gentle mounding and planting on the roundabout and planting on the embankments would soften the impact to slight adverse visual impact after 15 years. The 'underpass' option would have slight adverse visual impact for views across the AONB through loss of vegetation. Similarly, the provision of gentle mounding and planting on the roundabout would soften the impact to no change in visual impact after 15 years.
9.6 In terms of impact on groundwater, the 'underpass' would pose a high risk. Despite the need for substantial waterproof structures, groundwater may also need to be pumped to keep the new road free of water. The resultant de-watering on the local hydrology would have an adverse effect.
9.7 The 'overpass' option is more cost effective and has better economics than the 'underpass' option. The cost of the 'underpass' option would be around £6.0M more than the 'overpass' option with the need to permanently de-water and/or waterproof the cutting base, due to the presence of high groundwater. This means the 'underpass' would be poorer value for money than the overpass.
9.8 It is therefore considered that the 'underpass' is not a viable option and it is recommended that the 'overpass' option should be taken to public consultation as the proposed layout.
