Modelling Innovation - PC MOVA Hold MessagesDate: 2017-08-04 | Category: Research & Development
Modelling Innovation – PC MOVA Hold Messages
Two recent projects which Multimodal have undertaken has identified an issue with the traffic signal add-on – PC MOVA – being unable to accurately model hold messages within the external simulator.
A hold message requires a signal to be constantly sent, which cannot be set-up when configuring the PC MOVA connection file on its own.
As such Multimodal, in collaboration with Dan Preece at Integrated Traffic Services Ltd, have identified a workaround within PTV VISSIM.
This workaround uses 'dummy links' to send and maintain hold messages, with detectors and signal heads on the dummy link set to the appropriate phases on the junction.
The idea of the dummy link set-up is that when a signal turns green (which is linked to a phase on the junction), the traffic passes over the stop-line and runs over the MOVA detector. The detector, which has been linked within the PC MOVA Connection File, generates a demand and triggers a hold message. The constant flow of traffic keeps this hold message active until the phase turns red (in line with the associated phase at the signal controlled junction).
An example of the set-up is shown in Figure 1.
Figure 1 – Example Dummy Link Set-Up for Hold Messages
For each dummy link used to enable 'Hold' messages, the following network elements are required:
- A signal head which is linked to the appropriate phase;
- The associated MOVA detector placed after the stop-line;
- A vehicle input of 3600 vehicles/hour to model a constant demand; and
- A custom speed distribution (31mph) and driving behaviour (based on an Autonomous Vehicle Study carried out by PTV) to ensure constant link speeds, flows and close vehicle proximity.
To account for delayed hold messages, the detector on the dummy link is located a sufficient distance away from the signal head (see Figure 2), with the datasets amended to achieve the required clearance.
Figure 2 – Example Dummy Link Set-Up for Delayed Hold Messages
It is acknowledged that there may still be a slight lag and subsequent offset of the signals using this method (~two seconds), but the efficiency in the model is likely to counteract this and provides a better linking facility overall.
For more details on this, please email email@example.com.