Uncontrolled nodes

Note: For nodes of the control type uncontrolled and the Method for impedance at node Node impedance calculation (ICA), the Node VDF calculation method is used (Fundamentals: Uncontrolled nodes)..

1. Make sure the node input attributes Capacity PrT and t0 PrT (identical for all turns via the node) are set correctly for nodes of the control type uncontrolled.

2. Check and adjust the parameters on the Uncontrolled tab.

Element	Description
VD function	All VD functions are available for selection (Selecting VDFs for node types).
Maximum tCur	If this option has been selected, enter two values. The formula results in the user-defined maximum turn penalty at the node . Note Since any VDF can be selected and a maximum turn penalty tCur can be defined, resulting turn penalties are more realistic. If the BPR function is used with the default parameters a = 2, b = 4 and c = 1, the turn penalties for minor flows can be very high given full saturation. During route search these turns can then behave almost like blocked turns, which can cause severe fluctuations during assignment. Therefore it is recommendable to select parameters which ensure a lesser slope after saturation. This may be achieved with a parameter of b < 4 or better with the BPR2 function and b’= 1 if saturation exceeded 100%. Additionally it can be useful to set a maximum penalty. This is possible in the following form: tCur = MIN (tCur from node control VDF; t0 x Factor; Max tCur) Example with BPR function t0 = 20 s Saturation = 250 % a = 2, b = 4 tCur = 1583 s = 26.4 min Example with BPR2 function t0 = 20 s Saturation = 250 % a = 2, b = 4, b’ = 0.8 tCur = 103 s = 1.7 min A saturation of 250 % is not realistic in real life, but it may easily occur during assignment when the total volume is assigned to one shortest path. If you use the option Computing of tCur after assignment, please note that the shortest path algorithm will apply - to all turns - the tCur values available at the beginning of the assignment. These values are not reset, i.e they are not set to t0. Make sure, that t0 PrT > 0 applies to all relevant turns.

Element

Description

VD function

All VD functions are available for selection (Selecting VDFs for node types).

Maximum tCur

If this option has been selected, enter two values. The formula results in the user-defined maximum turn penalty at the node .

Note

Since any VDF can be selected and a maximum turn penalty tCur can be defined, resulting turn penalties are more realistic. If the BPR function is used with the default parameters a = 2, b = 4 and c = 1, the turn penalties for minor flows can be very high given full saturation. During route search these turns can then behave almost like blocked turns, which can cause severe fluctuations during assignment. Therefore it is recommendable to select parameters which ensure a lesser slope after saturation. This may be achieved with a parameter of b < 4 or better with the BPR2 function and b’= 1 if saturation exceeded 100%. Additionally it can be useful to set a maximum penalty. This is possible in the following form:

tCur = MIN (tCur from node control VDF; t0 x Factor; Max tCur)

Example with BPR function

t0 = 20 s

Saturation = 250 %

a = 2, b = 4

tCur = 1583 s = 26.4 min

Example with BPR2 function

t0 = 20 s

Saturation = 250 %

a = 2, b = 4, b’ = 0.8

tCur = 103 s = 1.7 min

A saturation of 250 % is not realistic in real life, but it may easily occur during assignment when the total volume is assigned to one shortest path. If you use the option Computing of tCur after assignment, please note that the shortest path algorithm will apply - to all turns - the tCur values available at the beginning of the assignment. These values are not reset, i.e they are not set to t0.

Make sure, that t0 PrT > 0 applies to all relevant turns.