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 Sydney’s transport system is being transformed with the introduction of a light rail system

complex road network environment will require an overhaul of the existing SCATS signal control strategies to cover various new light rail traffic signal priorities. The implementation of SCATSIM in the

Aimsun mesoscopic model has provided a precise estimate of the magnitude of traffic issues, allowing the development of more appropriate congestion manage- ment plans and evaluation of different signal priority levels and their impact on travel time reliability. There are some distinctive differences

in vehicle detection emulation between the microscopic and mesoscopic mod- els: the mesoscopic car-following model is simplified where the acceleration and deceleration constraints are removed. The model estimates the earliest time a vehicle can enter and exit the section, and uses this information to calculate vehicle presence at a particular detector. The first-of-its-kind SCATSIM interface

between SCATS and the mesoscopic model enables the exchange of informa- tion between SCATS and the simulator. In addition, a recently added microsimu-


lation pocket along the length of the light rail corridor can accurately replicate detailed light rail vehicle characteris- tics (such as length, acceleration and deceleration rates or speed profiles) and ultimately increase confidence levels in forecast travel times.

MODEL FORECAST VALIDATION The first big test for the CBD road net- work and the model’s ability to accu- rately forecast traffic conditions occurred in October 2015 during the implementa- tion of the new CBD Bus Plan and the first closures of George Street. The assess- ment of actual traffic volumes within the CBD cordon after the first closures showed a reduction in trip numbers and peak spreading away from the busiest time periods. This demonstrated the successes of the on-going travel man- agement campaign by the NSW trans- port authorities that aims at reducing vehicle numbers in Sydney CBD. The model results showed a 2 per cent overestimation of inbound and 16 per


cent underestimation of outbound vehi- cle trips in the AM peak period. This rela- tively high underestimation of outbound volumes was due to changeable nature of those trips with many multi-purpose trips. In terms of travel patterns, the model showed that in the AM peak traffic, diver- sions resulting from the proposed road closures and the new bus plan were likely to mainly occur on alternative north- south routes, which correlated closely with the survey data.

SUMMARY Overall, the use of the Aimsun model- ling platform in combination with SCATS provided a cutting-edge modelling tool that is able to successfully support the development of different demand man- agement and operational transport strat- egies. The platform will continue to serve different purposes and support decision making processes that will shape the future of Sydney transport network. ●

 Rob Dus is Director of Transport Analytics, GTA Consultants

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