The problem and the solution are illustrated using the example of "switching on a sound signal for the visually impaired".
- Requirement: The light signal (ls) can be enabled on its own, without the sound signal (ss).
As soon as the audio signal is switched, the light signal must also be active for the entire release time.
An interlock prevents the audio signal from being switched on during the release time of the light signal.
- vs | plus Parametrierung: A traffic stream with a separate request is provided for sighted and visually impaired pedestrians. The traffic stream for sighted pedestrians (TS 1) is assigned the signal group for the traffic signal as the main display element (DE 1).
The traffic stream for visually impaired pedestrians (TS 2) is assigned the signal group for the audible signal as the main display element (DE 2). In addition, UN-conditional traffic signal 1 is assigned. As a result, DE 1 is controlled by both traffic streams simultaneously. Once as the main display element and once as UN-conditional assignment. The two traffic streams are interlocked. TS 1 is the authoritative traffic stream, TS 2 is the dependent traffic stream.
- Problem: In vs | plus, the interlock is transferred from the traffic stream level to the display element level. During operation, this leads to the following problem (see following figure).
In the event of a request for traffic stream TS 2 after DE 1 has already received green, the interlock at the level of the traffic streams causes TS 1 to be closed when TS 2 is opened. TS 2 does not switch DE 1 as it is already open and at the same time the interlocking at the level of the display elements prevents the activation of DE 2. As a result, the audible signal remains silent for the entire release time.
Figure 48: Problems with interlocked traffic streams
- Solution: The problem has been revised in vs | plus 8.0.1. The interlocking check at the traffic stream level has been added to cover this case. In the specific case (see following illustration), the delay of the switch-on command to TS 2 means that DE 1 can close together with TS 1. This solves the interlocking of TS 2 with DE 1 and DE 2 can switch both display elements together.
