The New Standard for Traffic Model Runtime

Transport for London (TfL) is the integrated body responsible for London’s transport system. Its Operational Network Evaluator (ONE) is a tactical highway traffic assignment model, used to assess the impact of schemes in the Greater London area, and to evaluate mitigation strategies.

Built in PTV Visum software, ONE provides a simplified representation of real-world road traffic conditions. It is one of the largest and most detailed junction-based highway models in the world: It covers 5,692 zones; 53,500 kilometres of links; and over 17,000 junctions modelled in detail, of which more than 5,500 are signalised.

The ONE model in PTV Visum has been intensively used by TfL for many years, with excellent results. It has helped to assess the impact of schemes including cycle routes and major road redesign schemes. It also helped the operational analysis of road and river crossing closures, and their impact on bus journey times.

Recently, TfL updated the model with the latest version PTV Visum 2022, which includes a move from scripted to built-in assignment. As a result, the model sets a new standard for the industry for highway assignment runtimes on regular hardware. It converges within 2.5 hours, including a bespoke outer loop for taxi in bus-lane adjustments. Without this outer loop, which is unique to TfL’s application, the runtime would be even shorter - less than 1 hour!

These faster run times will significantly increase the computation resources available for the TfL team and speed up the assessment of transport schemes in London.