I want to add a growth factor to the base model, so that it automatically calculates the future growthed traffic flows.
In Junctions 9 this can be done using Demand Set Relationships and, optionally, Growth Factors. Some example uses are shown below.
Suppose you have a Demand Set D1, representing base year traffic flows and then want to have a second set D2 for future year traffic. Assume to begin with that the traffic growth is a uniform 20% for all movements on all approaches.
- Go to the properties of the D2 Demand Set, where you can enter its name, start/finish time and so on. Make sure that you are in Advanced Mode (turn this on via the main Data menu if needed).
- Tick the Use Relationship property.
- In the Relationship box, enter “D1 * 1.2”.
- When you look at the OD matrix when D2 is the active demand set, you should see that it is read-only and that the values in the OD matrix are automatically filled in as 120% of the base year values. They will update automatically if you alter the base year flows.
- This assumes use of the ONE HOUR profile (the default option). If using different profile types you may need to use different types of relationship – please contact us for details.
It is also possible to save one or more growth factors in the file:
- In the Data Outline, find the Growth Factors section (this comes after the Demand Sets). Right-click on it to add a new Growth Factor, which you can then edit.
- You can directly type in the growth factor value – for instance, enter 1.2 to use the 20% example from above.
- Then, in the D2 Demand Set, enter the Relationship as “D1 * G1”. The G1 will be replaced by the actual growth factor value when you view the D2 traffic.
- The advantage of this method is that you can enter a description explaining the source of the growth factor. By entering several growth factors you can also manage different scenarios such as high growth and low growth and so on.
- Optionally, if you tick the Use TEMPRO option, and then click the Calculate link, you can calculate TEMPRO growth factors based on the location, future year, road type etc. (This requires that you have the TEMPRO databases available on your PC or network.)
Now suppose that you have a separate development matrix representing additional future year traffic for each OD movement.
- Use D1 for the base year traffic, and D2 as the future year, as above
- Create a third Demand Set to store the development matrix. You can enter anything you like for the Demand Set ID, so this Demand Set could be labelled as D3, or as D999, or as D_DEV, or any other notation that you find useful. Simply enter the ID in the Demand Set’s properties. For this example assume it’s labelled as D_DEV.
- Make D_DEV active and enter the development traffic in the OD matrix.
- Edit D2 and set its Relationship to be “D1 + D_DEV”. The OD matrix for D2 should then be the sum of the base and development matrices.
- The development matrix can include negative values.
- If the development matrix is in the form of factors (e.g. 25% additional traffic for A-B), you can enter these as factors in the development matrix (e.g. 1.25) and then use a multiplication relationship (e.g. “D1 * D_DEV”)
You can combine relationships between multiple Demand Sets and the relationship can be any formula. For instance, “D1 * G1 + D2 * 0.5” is a valid relationship.
For more details, please see the User Guide.
NOTE: you can also quickly adjust traffic flows by editing the Network Flow Scaling Factor property on the current Analysis Set, and/or the scaling factors shown for each arm in the Demand Screen.