One of the most important features of SIDRA INTERSECTION is the modelling of signal platoons for signal coordination effects in network analysis. This is a unique lane-based platoon model derived using second-by-second arrival and departure flow patterns as a function of signal Offsets.
Unlike traditional network models that use aggregate models of links or lane groups, SIDRA INTERSECTION uses a lane-based model for platoon movements between upstream and downstream Sites (on internal approaches). This provides information about upstream departure and downstream arrival patterns, queue lengths, lane blockage probabilities, proportion of traffic arriving during green, and so on at an individual lane level.
The model applies to the internal approaches of two or more Coordinated Signal Sites that are connected to each other. The model also applies to two Coordinated Signal Sites with continuous lanes at a Site between them, for example Major Road lanes (treated as continuous lanes) of Two-Way Sign Control Sites, or continuous lanes at a seagull T intersection, between two Coordinated Signal Sites. The platoon patterns are moved from the upstream Site to downstream Site through the continuous lanes in this case.
The model takes into account midblock lane changes that apply to signal platoon patterns. This is particularly important in evaluating closely-spaced (paired) intersections with high demand flows where vehicles have limited opportunities for lane changes between intersections.
In addition to the Platoon Model using Signal Offsets, the older Simple Platoon Model using Arrival Types or Percent Arriving During Green continues to be available. Although its use is not recommended, it can be useful for example for external approaches of a Network.
Refer to the User Guide for detailed information on this subject. Also see the new papers on our Articles page.
For the second-by-second lane-based platoon model to apply to connected Signal Sites in a Network, you must ensure that the relevant input parameters are set correctly:
- In your older Projects, the Signal Coordination parameter may have been specified as Arrival Type or Percent Arriving during Green in the Signals tab in the Vehicle Movement Data input dialog for each Site. Change these to the Program option if you want the second-by-second lane-based platoon model to apply. Use the Reset to Defaults command for this purpose.
- Set the Reference Phase in the Phase & Sequence data tab of the Phasing & Timing dialog for each Site.
- Specify the signal coordination and other timing data (Coordinated Site, Reference Site, Signal Offsets (User or Program), Network Cycle Time) in the Network Timing dialog.
- Check the parameter Apply Platoon Dispersion in the Network Data dialog if you wish to include modelling of platoon dispersion.
Output related to signal coordination includes the Signal Offsets report for Networks, Signal Coordination report for Sites and Signal Coordination displays for Networks and Sites.
The Signal Offsets report gives the Offsets of Sites in the Network, and the Route Offset Results section of the report presents signal platoon characteristics and performance statistics for the movements that define the Route.
The Signal Coordination report presents detailed information on the results of second-by-second platoon patterns used in SIDRA INTERSECTION to model signal coordination effects of Signal Offsets. This Site report gives movement-based and lane-based signal coordination information including the Platoon Ratio, Percent Arriving During Green and Arrival Type determined by the second-by-second platoon model for individual internal approach movements and lanes.
The Platoon Ratio and other signal coordination parameters for movements are indicative of progression quality but they are not used directly in the performance models. Instead, the SIDRA INTERSECTION model uses signal coordination parameters determined for internal approach lanes. Using the Platoon Ratio parameter for each lane, SIDRA INTERSECTION calculates Delay Progression Factor and Queue Progression Factor parameters for use in performance calculations. These parameters are included in the Signal Coordination report as well as the LANE DELAYS, LANE QUEUES and LANE STOPS tables in the Detailed Output report.
Signal Coordination displays are colour coded according to Platoon Ratios and implied Arrival Types. They are presented as Lane Displays for Sites, Networks and Routes showing Signal Coordination characteristics per lane, and as Movement Displays for Sites showing Signal Coordination characteristics per movement.