There are three levels for the user control of the SIDRA Lane Blockage model. These are explained below.
The Capacity Adjustment parameter given in the Lane Geometry dialog, Lane Data tab (User Guide Section 5.4.3) should not be used for this purpose. The Capacity Adjustment parameter was introduced to adjust capacity in unusual cases when the calibration of all underlying parameters that determine capacity is not successful.
Lane Blockage Calibration Factor
The Lane Blockage Calibration Factor is the recommended lane-level parameter that provides a detailed method for calibrating the lane blockage model (User Guide Figure 8.2.18). It is given in the Site Lane Movements dialog, Blockage Calibration tab (User Guide Section 5.5.2).
The Lane Blockage Calibration Factor applies to Probability of Blockage used in the capacity adjustment of the subject approach lane due to lane blockage by exit lane queues as determined for the downstream Site in Network analysis.
The default value of this parameter is 1.0. Values of this parameter below 1.0 will decrease the effect of lane blockage, and parameter values above 1.0 will increase the effect of lane blockage.
The Lane Movement Flow Proportions specified in the Flow Proportions tab of this dialog are also used in subject lane capacity adjustments for lane blockage.
Blockage Tolerance
The Blockage Tolerance parameter is a Site-level general parameter that may be used in association with the lane blockage model (User Guide Figure 8.2.19). It is given in the Site Parameter Settings dialog, Model Parameters tab (User Guide Section 5.14.2) as a tolerance factor in approach lane capacity adjustment for downstream lane blockage applicable to all lane movements on all approaches of a specific Site.
The Blockage Tolerance value reduces the Capacity Reduction amount corresponding to the Probability of Blockage for all lanes of the Site. It is subtracted from the Probability of Blockage in reducing the capacity of the upstream lane to allow for the effect of downstream lane blockage.
The default value of the Blockage Tolerance parameter is zero (no effect on Capacity Reduction calculations).
Apply Lane Blockage Model
The Apply Lane Blockage Model check box in the Network Data dialog (User Guide Section 6.4.1) allows the user to have SIDRA do modelling for a specific Network with the lane blockage model turned off (User Guide Figure 8.2.20). This parameter is provided for unusual use, e.g. to inspect the extent of the effect of lane blockage on Network analysis results including Network signal timings.
In normal use of SIDRA, it is not recommended to uncheck this check box.