TFGAP-S Examples 4B.

TFGAP Static Service -- Examples 4B.
Version of 15 October 2005
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Terminating the FGD without using the FYD. During the years that the FYD is being retired from its traditional purpose, an alternate method of terminating the FGD phase is needed. Table 4B1 shows one possibility, where Vine Street starts with an SGD and Elm Street an FGD. Unlike the tables in section 4A, each table on this page contains a sequence of signals.

Table 4B1
Step Vine Street Elm Street Duration Comments
1 Hours The starting long-term state.
2 3-6 sec Yellow clearance for Vine.
3 3-6 sec Red clearance for Vine.
4 10-20 sec Upgrade of Elm's green from flashing to steady. This must last long enough so that Elm Street drivers can tell that flashing has stopped.
5 3-6 sec Yellow clearance for Elm.
6 3-6 sec Red clearance for all.
7 Any desired signals.

Table 4B1
Step	Vine Street	Elm Street	Duration	Comments
1			Hours	The starting long-term state.
2			3-6 sec	Yellow clearance for Vine.
3			3-6 sec	Red clearance for Vine.
4			10-20 sec	Upgrade of Elm's green from flashing to steady. This must last long enough so that Elm Street drivers can tell that flashing has stopped.
5			3-6 sec	Yellow clearance for Elm.
6			3-6 sec	Red clearance for all.
7	Any desired signals.

Although a few highway departments have installed arrows as yield signals, practically none have implemented dots for this purpose. Reports of experience with yield dots are not to be found, so we have shown in the table above what is probably is the maximum level of articulation, to illustrate all the possibilities to the signal designer. Also, the durations are merely estimates of what times might be effective.

Options are to omit step 3, a partial red clearance; and to omit step 6, the full red clearance. Table 4B2 contains the shortest feasible schedule:

Table 4B2
Step Vine Street Elm Street Duration
1 Hours
2 3-6 sec
4 10-20 sec
5 3-6 sec
7 Any desired signals.

Table 4B2
Step	Vine Street	Elm Street	Duration
1			Hours
2			3-6 sec
4			10-20 sec
5			3-6 sec
7	Any desired signals.

Table 4B3 shows how to convert the some-way yield to the all-way stop.

Table 4B3
Step Vine Street Elm Street Duration
1 Hours
2 3-6 sec
3 10-20 sec
4 3-6 sec
5 Hours

Table 4B3
Step	Vine Street	Elm Street	Duration
1			Hours
2			3-6 sec
3			10-20 sec
4			3-6 sec
5			Hours

Terminating the FGD with benefit of the FYD. Like previous examples, this one starts Vine Street with an SGD and Elm Street with an FGD. The SGD changes to SYD thence to SRD, and the FGD changes to FYD thence to SRD. These four signal changes can occur in a variety of sequences, and some of them can take place simultaneously. Table 4B4 details one way to schedule them:

Table 4B4
Step Vine Street Elm Street Duration
1 Hours
2 3-6 sec
3 3-6 sec
4 3-6 sec
5 3-6 sec
6 Any desired signals.

Table 4B4
Step	Vine Street	Elm Street	Duration
1			Hours
2			3-6 sec
3			3-6 sec
4			3-6 sec
5			3-6 sec
6	Any desired signals.

In table 4B5 the yellows are presented in the opposite order:

Table 4B5
Step Vine Street Elm Street Duration
1 Hours
2 3-6 sec
3 3-6 sec
4 3-6 sec
5 3-6 sec
6 Any desired signals.

Table 4B5
Step	Vine Street	Elm Street	Duration
1			Hours
2			3-6 sec
3			3-6 sec
4			3-6 sec
5			3-6 sec
6	Any desired signals.

And in table 4B6 the yellows are displayed at the same time:

Table 4B6
Step Vine Street Elm Street Duration
1 Hours
2 3-6 sec
3 3-6 sec
4 Any desired signals.

Table 4B6
Step	Vine Street	Elm Street	Duration
1			Hours
2			3-6 sec
3			3-6 sec
4	Any desired signals.

Other plans, some involving partially overlapping yellows, are possible. The research needed to select one schedule over another is not yet available.