SOME of the mentions of traffic reductions
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For the purposes of this assessment, the city centre has been defined as the current Low Emissions Zone (LEZ) boundary. The development of options within this boundary has examined ways in which the city centre’s streets can be transformed to meet the policy objectives and benefits described above, and to understand the operational issues of doing so.
The overall aim is to enhance the place value of the city centre and strengthen the size, quality and ease-of- understanding of the Pedestrian Priority Zone (PPZ) that was defined by ECCT, while supporting a reduction in private vehicle trips across the city centre. In doing so, the options examine existing and planned street improvement projects, but identify ways in which these projects can be cast within holistic and intuitive plans for all users of the city centre’s streets, rather than at a project-specific level.
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Development of the business case for future tram is currently in progress. However, work undertaken to date indicates a preference for a route to the south via the Bridges corridor. Construction of tram would be a major step change in public transport provision and would provide a fast and efficient alternative to the car. Tram operation would require a significant reduction in traffic volumes on the Bridges corridor. At this stage, a bus gate/junction layout changes would need to be considered for North Bridge that would restrict through Our Future Streets (Circulation Plan) – Technical Summary Report
traffic. Local access would be maintained throughout the day with a connection maintained at Chambers Street.
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All options have been tested using the council’s Strategic and Microsimulation models to understand wider and local impacts. Analysis has considered both current traffic levels and a 30% reduction in demand, reflecting Edinburgh’s car kilometre reduction targets. Additional sensitivity testing has been undertaken to assess the implications of potential Holyrood Park restrictions.
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Traffic evaporation is potentially in the order of 10% of existing trips (see inset below). Therefore, other policy interventions would be required to deliver a 30% reduction as per the car kilometre target set by the Council, potentially including further parking restrictions, a workplace parking levy and/or road user charging. Given this, careful consideration should be given to the implementation of the preferred option to minimise the impact on public transport. Early messaging and guidance to drivers and other users can help offset the immediate impact of major network changes. Frequently, it is the first weeks of a scheme that have the greatest negative impact on congestion - and there is the potential for the transport model to significantly underestimate this. In the medium term, impacts settle to an as modelled condition (or better) as traffic evaporation and behaviour change takes place.
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Based on 2016 observed data and subsequent 2019 validation, which helped develop Edinburgh’s suite of traffic models, there are approximately 17,000 vehicle trips (car, LGV and HGV) per hour in the city centre during the peaks, with approximately 30% of these trips not having an origin or destination within the city centre study area. Although this figure aligns with Edinburgh’s traffic reduction target, discouraging these trips from the city centre is anticipated to increase kilometres travelled as vehicles navigate around the city centre. A citywide 30% reduction in general traffic would remove approximately 13% of strategic trips from Edinburgh City Centre. At a high-level and including a margin of error and optimism bias, this suggests a maximum figure possible in the city centre for ‘traffic evaporation’ of around 10%. The remaining traffic reduction required to meet Edinburgh’s 30% target for the city centre will have to be delivered through mode shift to public transport and walking, wheeling and cycling. Assuming a typical car occupancy rate of 1.3 people per vehicle, 20% of 17,000 trips would equate to around 1,800 people per hour. To put this volume of people into context, this would fill 23 double decker buses per hour. This highlights that future options for Edinburgh’s city centre must discourage unnecessary trips but also provide sufficient high quality public transport and walking, wheeling and cycling provision if the 30% vehicle kilometre target is to be met.
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For the city to achieve these targets as a whole, the city centre will play a significant part in managing citywide demand. For the city to achieve these targets in just six years’ time, the city centre will require a significant reduction in general traffic in the short term. Therefore, there is a strong case to go further than the current ECCT proposals to expedite the changes needed to the city centre transport network and meet the Council’s policy objectives.
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