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The collection of actual traffic delays and road traffic speed data is essential in modelling urban transport resource efficiency, congestion and carbon and pollutant emissions, which is in turn part of core empirical basis for evidence-based policy making for improving urban sustainability. This data collection has also been one of the most expensive and time-consuming tasks, which restricts how well and how often the models can be built and validated, often to the extent that urban transport models have to rely on severely outdated data with sparse coverage. New smart data such as GPS vehicle traces has raised the prospect of remedying the data shortage, but for operational and data protection reasons often only low-sampling frequency traces are available. This paper proposes a novel method for estimating actual, congested link-speeds from lowsampling frequency taxi GPS traces that are publicly available. The method is based on a path inference process and is applied over a detailed road network in a large city region. It shows that low frequency GPS trajectories can significantly improve the spatial and temporal resolutions of traffic speed data for transport modelling and policy analysis. This opens up the prospect of improving road operation performance, managing travel demand and optimizing urban circulation.

This paper examines changes in travel behaviour associated with ridership on the Jubilee Line Extension in east London and the resulting impacts on greenhouse gas (GHG) emissions. The paper looks at initial changes in mode choice after the line opened in 1999 and ongoing mode share trends through to 2011. The initial mode shift is assessed through an analysis of published travel survey data and the annual TfL Rolling Origin Destination Survey. Longitudinal changes in mode share are assessed using the London Travel Demand Survey and the relationship between metro accessibility and mode choice. From 2000 to 2011 the calculated GHG savings are 338 ktCO2e; approximately equivalent to the annual average GHG emissions of 43,000 UK residents.

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