ADVANCED SOFTWARE FOR SIGNAL ANALYSIS
SIDRA INTERSECTION is a powerful software package for timing, capacity, performance and level of service analysis of signalised intersections (junctions controlled by traffic lights) including signal coordination effects. It uses an advanced critical movement analysis method allowing for overlap movements and movements with two green periods per cycle. The method was first published in ARRB Research Report ARR No. 123 by Dr Rahmi Akçelik. "SIDRA" was first released in 1984 as the software which implemented the ARR 123 signal capacity and timing analysis methodology.
Refer to our Resources - Articles page for a reprint of ARR No. 123 and many other important papers and reports that explain fundamental aspects of signal analysis methods used in SIDRA INTERSECTION.
TRAFFIC SIGNAL TIMING
SIDRA INTERSECTION uses powerful methods for determining signal timings using fixed-time (pretimed) and actuated signal analysis methods for any intersection geometry allowing for simple as well as complex phasing arrangements involving overlap movements. Practical cycle time, optimum cycle time, user-given cycle time and user-given phase times options are available. Advanced signal timing options available in SIDRA INTERSECTION include green split priority for coordinated movements, equal and unequal target degrees of saturation, cycle time optimisation for fixed-time / pretimed signals or coordinated actuated signals, and maximum green optimisation for actuated signals.
US STUDY OF ALTERNATIVE TRAFFIC MODELS FOR SIGNALISED INTERSECTIONS
North Carolina State University carried out a comprehensive study and evaluation of alternative software packages for signalised intersections for the North Carolina Department of Transportation. In addition to SIDRA, the packages evaluated were HCS/HCM, Signal 94, HCM/Cinema, EVIPAS and TRANSYT 7F. SIDRA was rated best on all accounts and recommended for use as the standard model. Average ratings were as follows.
- Model Usability: SIDRA received 4.1 / 5 (HCM/HCS received 3.2 / 5, TRANSYT 7F received 3.3 / 5).
- Model Optimisation (the quality of signal optimisation plan): SIDRA received 4 / 5 (TRANSYT 7F received 2 / 5, Signal 94/HCM received 3 / 5).
- Model Evaluation (the degree to which the model delay results match field delays): Step-wise regression between observed and predicted delays showed that SIDRA was the best delay model (highest R-squared value and least number of explanatory variables). SIDRA received 4.5 / 5 (HCS/HCM received 3 / 5, TRANSYT 7F received 4 / 5).
CLICK, S.M. and ROUPHAIL, N.M. (1998). Field Assessment of the Performance of Computer-Based Signal Timing Models at Individual Intersections in North Carolina. Report for the North Carolina Department of Transportation. Center for Transportation Engineering Studies, Department of Civil Engineering, North Carolina State University.
SIGNAL MODEL FEATURES
SIDRA INTERSECTION models for analysis of traffic signals include turn on red (RTOR or LTOR), semi-actuated signals, and allow for such features as undetected movements, dummy movements and phase transition data. Graphical input method can be used for easy specification of phasing and timing data including known phase times.
For intersections running under the SCATS control system, fixed-time / pretimed analysis method available in SIDRA INTERSECTION can be used to emulate equal degree of saturation method used by SCATS for green splits.
SIDRA INTERSECTION output includes estimates of SCATS parameters maximum flow and headway, occupancy time and space time at maximum flow. These parameters, together with the SCATS lane flow data can be used for model calibration purposes where applicable.
CYCLE TIME & GREENSPLIT OPTIONS
SIDRA INTERSECTION offers different options to specify the desired method of cycle time calculation for traffic signals (subject to minimum and maximum cycle time constraints):
Practical Cycle Time: A cycle time (and green times) that satisfy the practical (target) degree of saturation for critical movements are determined.
Optimum Cycle Time: A cycle time that optimises a selected performance measure is determined for fixed-time (pretimed) or coordinated actuated signals. One of a large number of options can be chosen as the performance function to determine the best cycle time.
User-Given Cycle Time: The green times using the given cycle time are determined for fixed-time (pretimed) or coordinated actuated signals.
User-Given Phase Times: The phase times given for the selected sequence are used. In this case, the phase times are added to determine the cycle time.
The Green Split Priority option is available for the allocation of longer green times to coordinated movements while keeping other movements at their target (practical) degree of saturation levels.
Parameters for Actuated Signal timing analysis include Maximum Green Setting, Gap Setting and Effective Detection Zone Length. Actuated signal timings can be optimised by varying the Maximum Green Settings.