Portsmouth City Council Local Plan – Modelling & Transport Assessment

Portsmouth City Council Local Plan – Modelling & Transport Assessment

The Challenge

SYSTRA was commissioned by Portsmouth City Council in 2018 for support with the new Local Plan, primarily to evaluate the impact of proposed developments within allocated sites on the surrounding transport network at a local and strategic scale. The new Local Plan for Portsmouth will set out the planning strategy for meeting future development needs in the city for the period up to 2036 and builds on previous iterations. This commission ran in conjunction with modelling associated with a bid to the Transforming Cities Fund, seeking to implement a Bus Rapid Transit network across the city and the adjacent metropolitan areas.

SYSTRA’s Role

SYSTRA first conducted a review of the locations of the allocated sites in the context of the strategic highway network and local junctions. The council’s own strategic model was used to give an overview of future scenarios and summarise key changes to inform the detailed junction modelling and design work. This process enabled high priority junctions to be identified from congestion hotspots for further assessment.

SYSTRA subsequently built models for over 20 junctions on the highway network, each containing seven scenarios over three future years. This wide-reaching assessment enabled the impact of committed growth to be observed and subsequently determined whether further mitigation measures were necessary or appropriate. Mitigation schemes, as well as cost estimates, were developed to help alleviate capacity issues for seven junctions. In addition, SYSTRA conducted a sensitivity test for one junction which was subject to significant capacity constraints. The mitigation scheme for this junction resulted in the removal of pedestrian crossings on one side of the roundabout. It was considered a more beneficial course of action would be to determine the impact of the mitigation scheme on the surrounding highway network in isolation and weigh up whether the positive vehicular impacts outweighed any detriment to active travel modes.

The development of all mitigation options looked to balance the needs for vehicular and vulnerable road users, in order to support council policy aims of improving air quality and conditions for pedestrians and cyclists.

SYSTRA submitted a Transport Assessment supporting the evidence base to inform the Local Plan development, providing a robust assessment of the forecast impact of the proposed development allocations on the local and strategic highway network across the Portsmouth area. The conclusions balanced priorities for the junctions based on junction locations, opportunities for improvement whilst considering available highway boundary, Bus Rapid Transit design proposals and proximity to Strategic Allocation sites. The Local Plan is currently being prepared for full public consultation.

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