TRANSYT is a software suite containing a macroscopic traffic model, signal optimisers, and a simulation model for the purposes of designing, evaluating and modelling everything from single isolated road junctions to large mixed coordinated signal-controlled and priority-controlled traffic networks.
How it Works:
The core traffic model calculates a baseline Performance Index (an economic cost based on stops and delays) using manually entered traffic flows. TRANSYT then runs an optimisation process that adjusts the signal timings with the ultimate aim of reducing the Performance Index (PI) to a minimum. The TRANSYT optimisers are therefore seeking to produce multi-directional ‘green waves’ – a task that is impractical to attempt manually due to the complexity of trying to satisfy multiple objectives from different parts of the network. Green waves on key routes can be easily favoured by applying constraints on the optimiser in the form of weightings and penalties.
A number of optimisers are provided and offer a choice between fast and highly-efficient modelling and slower modelling options which are able to provide better optimised timings. The optimisation process can be influenced by the application of a variety of weighting factors and limit penalties to the PI, that allows you to ensure the results match your exact criteria.
The simulation model provides a mechanism to evaluate the performance of a network for a given set of signal timings, for a wider variety of scenarios, including intermittent stages (i.e. non cyclic behaviour), vehicle actuated signals, blocking back, uneven lane usage, complex signalled approaches and controller streams on different cycle times. This is achieved by modelling the random arrival patterns of individual vehicles over a series of trials, with results collated from the output of all trials.
TRANSYT’s main capabilities:
Large networks of signalled junctions, long arterial routes (including green waves), and mixed signalled and unsignalled networks can be easily and quickly modelled using TRANSYT. TRANSYT will produce the right output to allow you to evaluate the performance of existing layouts and signal timings. Future scenarios (new layouts, new flows) can similarly be investigated, and new optimised timings produced for a range of predictions – with different flows and signal timings (analysis sets) all stored within the one file.
Individual signalised or unsignalled junctions (with and without internal stop lines) can be easily modelled in TRANSYT. Using the TRANSYT Library file system also makes junction construction simple and fast.
The model can be constructed either using a traditional link structure or using TRANSYT’s lane and traffic stream structure, which allows a direct ‘one real lane’ to ‘one model lane’ representation.
The model also provides for give-way priority control, including the modelling of opposed right-turn traffic within signal controlled junctions. Standard ARCADY and PICADY geometric data can be specified in order to calculate and assign the required give-way coefficients to the network* – all within the one data file. TRANSYT provides a fast and efficient way of comparing alternative signalled, unsignalled, and partially signalled solutions within the one product
Fully-signalised and partially-signalised roundabouts can be modelled and their delay minimised by calculating timings which reduce blocking-back by keeping the circulating carriageway free flowing. Where blocking cannot be prevented TRANSYT’s cell-transmission model can be used to model its effects, or alternatively the simulation model can be used if signal optimisation is not required. Totally unsignalled roundabouts can also be modelled, and when included in a network, the effects of such roundabouts on the network are accurately represented, and the co-ordination can be optimised.
Weighting factors, queue-length penalties, and degree-of-saturation penalties can be applied to individual links or lanes in order to encourage the optimiser to produce timings that avoid queues beyond a certain length or to reduce delays on specific links. Such penalties can be used when modelling network arterials. You can ensure that arterial roads are kept flowing by prioritising them through the use of TRANSYT’s weighting-influenced optimised signal timings.
The program can be used to produce timings which give priority to buses or trams without the need to detect individual special vehicles within mixed traffic streams.
TRANSYT includes the accurate modelling of flared (short lane) signalled approaches. This is particularly important in modelling signalised roundabout approaches where flares are common.
Both isolated and ‘within junction’ signalled pedestrian crossings can be represented within the TRANSYT network model and the provision of green times for pedestrians reported.
Following a large research project undertaken by TRL for Transport for London in 2012, TRANSYT has been developed to use a unique walk-on-red pedestrian behaviour model. The model addresses shortcomings in macroscopic models that have not modelled pedestrians who gap-accept; only modelling pedestrians who cross at the green man. The pedestrian behaviour at traffic signals modelling algorithm used within TRANSYT is used under licence from Transport for London.
TRANSYT can also model time-varying traffic conditions by splitting the modelled period into time slices. Queue and delay results are generated for each time slice as well as for the overall situation. Signal timings are optimised for the complete time period.
TRANSYT is naturally suitable for both drive-on-the-left and drive-on-the-right operation.
*Requires an active ARCADY 7 (or later) and/or PICADY 5 licence (or later).