SIDRA for Highway Capacity Manual (HCM)

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The Highway Capacity Manual (HCM) Setup in SIDRA INTERSECTION

SIDRA INTERSECTION software complements the Highway Capacity Manual (HCM) as an advanced intersection and network analysis tool. The Highway Capacity Manual (HCM) Setup in SIDRA INTERSECTION offers options for US Customary and Metric units.

SIDRA INTERSECTION is compatible with the Highway Capacity Manual. However, unlike other software packages, the HCM Setup in SIDRA INTERSECTION does not claim to be a simple replication of the HCM procedures. Instead, SIDRA INTERSECTION offers various extensions on the capabilities HCM offers.

SIDRA INTERSECTION offers powerful extensions to the Highway Capacity Manual (HCM)

For all types of intersection, SIDRA INTERSECTION uses more advanced models and methods, including lane-based intersection and network analysis (rather than analysis by lane groups), modelling of complex short lane cases, detailed modelling of geometric delays, modelling of Two Way Yield (Give way) Sign Control and roundabout metering signals, Turn On Red by gap acceptance modelling, capacity constraint, lane blockage and midblock lane changes in network analysis, and the use of drive cycles (cruise, acceleration, deceleration and idling) for detailed modelling of delay and travel time components as well as operating cost, fuel consumption and emission estimation.

A detailed paper on the HCM setup of SIDRA was published by Akçelik (1990). Some aspects of this paper are outdated due to the changes introduced in later editions of HCM and the adoption of those changes in SIDRA INTERSECTION. Detailed explanations related to all aspects of the HCM version of SIDRA INTERSECTION are included in the SIDRA INTERSECTION User Guide.

Calibration and model options

The HCM and SIDRA INTERSECTION capacity and performance models are compatible in their basic structures and principles. Making use of this compatibility, the HCM software setup in SIDRA INTERSECTION is based on the calibration of most model parameters using the HCM defaults as applicable.

SIDRA INTERSECTION includes facilities to allow the user to choose between the HCM and SIDRA Standard model options including Roundabout Capacity Model options (SIDRA Standard, HCM 6, HCM 2010), HCM Delay and Queue Model options, and option to include Geometric Delay.

HCM models and methods in SIDRA INTERSECTION

Various HCM models or methods are used in all software setups of SIDRA INTERSECTION, including the HCM Level of Service method and criteria, the delay and queue progression factors for signal coordination effects, and pedestrian effects on capacity at signals, roundabouts and sign-controlled intersections. SIDRA INTERSECTION uses lane-based versions of these methods.

Roundabouts

SIDRA INTERSECTION includes a full implementation of the roundabout capacity models described in HCM Edition 6 and HCM 2010 in addition to the SIDRA Standard model calibrated to match the HCM Edition 6 model. SIDRA INTERSECTION offers powerful extensions to these models to enhance your roundabout design capabilities.

The SIDRA Standard roundabout capacity model includes the effect of roundabout geometry parameters (roundabout size, circulating road width, entry radius and angle, etc.) and allows reduction in Critical Gap and Follow-Up Headway with increasing demand flows (important in design life analysis).

The roundabout capacity model is the only analysis method in the HCM which uses lane-by-lane analysis, and as such it is best implemented by SIDRA INTERSECTION which has been using a lane-based model for all types of intersection since the 1984 and for networks since 2013.

According to the US Transportation Research Board document "Roundabout Practices", SIDRA INTERSECTION is the most widely-used software tool in the USA for roundabout capacity and performance analysis.

Signalised Intersections

In addition to the general features mentioned above, advanced signal timing methods are available including variable phasing analysis, multiple phase sequence analysis, and green split priority for coordinated or user-specified priority movements. The use of two green periods for modelling slip / bypass lanes, Turn On Red (RTOR) and permitted-protected left-turns provides more accurate capacity estimates. Network modelling includes a unique lane-based second-by-second platoon progression method. Network signal timing methods are available to determine cycle time, green times and signal offsets for coordination of signalised intersections controlled by separate signal controllers as well as Common Control Group timings for intersections running under a single signal controller.

Sign Control

Important common aspects of Two Way Sign Control (TWSC) capacity and performance models in SIDRA INTERSECTION and HCM include:

  • gap acceptance method with consistent values of Critical Gap (Headway) and Follow-up Headway parameters (some minor differences may exist),
  • capacity and delay equations (the HCM equations are used in the HCM software setup of SIDRA by default but they are applied to lanes rather than movements), and
  • the same method for basic shared lane capacity.

However, because the SIDRA capacity and performance model for TWSC intersections is a lane-based model compared with the HCM lane-group based model, some differences exist between the SIDRA and HCM methods for TWSC intersections (discussed in detail in the SIDRA INTERSECTION User Guide). HCM TWSC method is limited to Stop Sign Control while SIDRA INTERSECTION includes modelling of Yield (Give Way) Sign Control.

For the AWSC model in SIDRA INTERTSECTION, specifying the Departure Headway parameter determined from the HCM 6 method as input is recommended.

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