Sidra Intersection

Sidra Intersection (previously called Sidra and aaSidra) is a software package used for intersection (junction) and network capacity, level of service and performance analysis by traffic design, operations and planning professionals. First released in 1984, it has been under continuous development in response to user feedback. A new major version with network modelling capability and new vehicle movement classes was released in April 2013.

Sidra Intersection is a micro-analytical traffic evaluation tool that employs lane-by-lane and vehicle drive cycle models. It can be used to compare alternative treatments of individual intersections and networks of intersections involving signalised intersections (fixed-time/pretimed and actuated), roundabouts (unsignalised), roundabouts with metering signals, fully signalised roundabouts, two-way stop and give-way (yield) sign control, all-way (4-way and 3-way) stop sign control, merging, single-point urban interchanges, traditional diamond and diverging diamond interchanges, basic freeway segments, signalised and unsignalised midblock crossings for pedestrians, and merging analysis.

Sidra Intersection allows modelling of separate Movement Classes (Light Vehicles, Heavy Vehicles, Buses, Bicycles, Large Trucks, Light Rail/Trams and two User Classes) with different vehicle characteristics. These movements can be allocated to different lanes, lane segments and signal phases; for example for modelling bus priority lanes and signals.

In Australia and New Zealand, Sidra Intersection is endorsed by Austroads. In the USA, Sidra Intersection is recognised by the US Highway Capacity Manual, TRB/FHWA 2010 Roundabout Guide (NCHRP Report 672) and various local roundabout guides.

Lane-based intersection analysis method

The lane-by-lane capacity and performance analysis method used by Sidra Intersection helps to identify any de facto exclusive lanes, unequal lane utilisation, modelling of short lanes (turn bays, lanes with parking upstream, and loss of a lane at the exit side) and lane blockage in shared lanes including lanes containing opposed (permitted) turns, slip (bypass) lane movements and turns on red. Intersections with up to 8 legs (approaches) can be modelled in detail using this method with advantages over approach-based and lane group based methods.

Network model

SIDRA NETWORK model provides a lane-based congestion modelling tool. It determines the backward spread of congestion as queues on downstream lanes block upstream lanes, and applies capacity constraint to oversaturated upstream lanes; thus limiting the flows entering downstream lanes. These two elements are highly interactive with opposite effects. A network-wide iterative process is used to find a solution that balances these opposite effects. The lane-based network model provides information about departure and arrival patterns, queue lengths, lane blockage probabilities, backward spread of queues, and so on at a lane level. The model allows for the effect of upstream lane use patterns on downstream signal platoon patterns, in turn affecting the estimates of network performance measures (travel time, delay, back of queue, stop rate). This is important especially in evaluating closely spaced intersections with high demand flows where vehicles have limited opportunities for lane changing between intersections. The modelling of arrival patterns at downstream approach lanes takes into account implied midblock lane changes. Different movement classes (light and heavy vehicles, buses, large trucks, bicycles, and so on) are treated individually in modelling platoon arrival and departure patterns.

Performance measures

Sidra Intersection provides a large number of intersection and network performance measures and a number of alternative Level of Service (LOS) methods and LOS Target settings to determine acceptable intersection and network design. Standard performance measures such as delay, queue length and number of stops as well as measures to help with environmental impacts and economic analysis are provided. Performance and Level of Service results are given at various aggregation levels (individual lanes, individual movements, approaches, and intersection) and separately for vehicles, pedestrians, and persons (results for pedestrians and people in vehicles combined).

Roundabouts

Sidra Intersection allows analysis of single-lane and multi-lane roundabouts. It employs a combined (hybrid) geometry and gap-acceptance modelling approach in order to take into account the effect of roundabout geometry on driver behaviour directly through gap-acceptance modelling. Sidra Intersection software includes templates for roundabouts including all roundabout examples given in MUTCD 2009 and TRB/FHWA 2010 Roundabout Informational Guide (NCHRP Report 672). A Roundabout Metering analysis method allows the evaluation of the effect of metering signals on roundabout capacity and performance. Metering signals help to solve the problem of excessive queuing and delays at approaches affected by unbalanced traffic streams at roundabouts. Fully signalised roundabouts can be modelled as a network.

Model calibration

Sidra Intersection provides facilities to calibrate the traffic model for local traffic conditions including standard models and options for different countries, customised models prepared by users, detailed model parameters for the user to specify input data and model settings to match real-life traffic conditions, a sensitivity analysis facility to allow testing of the effect of variations in values of key parameters, and various calibration techniques (including survey methods) described in the User Guide.

Emissions and energy

Sidra Intersection estimates the cost, energy and air pollution implications of intersection design using a four-mode elemental model with detailed acceleration, deceleration, idling and cruise elements. This drive-cycle (modal analysis) method coupled with a power-based vehicle model is used to estimate operating cost, fuel consumption, greenhouse gas (CO2) and pollutant (CO, NOx, HC) emissions in order to assess the environmental impacts of traffic congestion. The model includes estimates of acceleration and deceleration times and distances for light and heavy vehicles coupled with a polynomial model of acceleration-time profile. The vehicle parameters in the model have been updated recently for modern vehicle fleet.

Highway Capacity Manual

Sidra Intersection software complements Highway Capacity Manual (HCM 2010) as an advanced intersection analysis tool which offers various extensions on the capabilities of the HCM. The Highway Capacity Manual version of Sidra Intersection has options for US Customary and Metric units. The roundabout capacity model for single-lane and multi-lane roundabouts based on research on US roundabouts as described in HCM 2010, Chapter 21 is integrated into the software. The HCM 2010 roundabout capacity model is a lane-based model which is suitable for the extensions implemented in Sidra Intersection.

Scientific foundation and awards

File:Rahmi Akçelik crop.jpg

Dr Rahmi Akçelik in 2012

Sidra Intersection was first developed over 20 years at the Australian Road Research Board (1979–1999) as a technology transfer tool to enable practitioners to use major research results without delay, and then at Akcelik and Associates since 2000. Akcelik and Associates conducts its own research as well as using the latest research results which become available internationally including the Highway Capacity Manual. Thus Sidra Intersection includes high technical content based on extensive scientific research. A formal "effectiveness audit" of related research carried out by an independent panel formed by the Australian Road Research Board in 1993 noted "the panel rated the technical merit of the research as very high and concluded that it has established international and professional reputations in the fields of traffic signal analysis, roundabout analysis, and energy and emissions modelling".

The company has won awards including the 2010 Telstra Business Awards - AMP Innovation Award and the 2009 the Governor of Victoria Export Awards - Winner Small Business Award. The awards received by the founder of the company, Dr Rahmi Akcelik, includes the prestigious 1999 Clunies Ross National Science and Technology award for outstanding contribution to the application of science and technology in Australia, and the Institute of Transportation Engineers (USA) 1986 Transportation Energy Conservation Award in Memory of Frederick A. Wagner for research into energy savings from urban traffic management (received as part of the energy research team at the Australian Road Research Board).

External links

• Official website
• Telstra Business Awards History
• The Australian Export Awards
• ATSE Clunies Ross Foundation
• Australian Road Research Board (ARRB)