Public Transport Access Levels (PTALs) are calculated across London using a grid of points at 100m intervals. For each point walk time to the public transport network is combined with service wait time (frequency) to give a measure of public transport network density.

TfL has made pre-calculated PTALs available on WebCAT, its web-based connectivity assessment toolkit (www.tfl.gov.uk/WebCAT). Users can view PTALs for any location in London alongside contextual information such as the local street network, rail stations and bus stops. Users can also view the PTALs resulting from planned improvements to and extensions of the public transport network. A limitation of PTALs is that they only reflect access to the public transport network, but not the opportunities and services reachable through the network. To address this, WebCAT also includes travel time mapping and catchment statistics (population, jobs, town centres, heath services and educational establishments) within given time bands. These can also be viewed for any selected location and combined with PTAL to give a more complete picture of public transport connectivity.

TfL may refine how PTALs and WebCAT operate but will consult on any proposed changes with stakeholders in advance. This may include an opportunity for users to assess connectivity in relation to cycling time to the public transport network rather than just walking time.