Specifications

7-15
Since the threshold of 50 has already been obtained,
the leading limit computation would want to set the max
timer to 0 (actually 1 is the lowest value it will load).
However, since the max timer has timed only 10
seconds (30-20), the group max timing computation will
want to set it to 5-- meeting the group max time
requirement of 15 seconds total green. Since 5 is
higher than 0, the max timer will change its current
value of 20 to 5.
-Scenario 2. Say the current cycle timer is only at 40
while the phase’s max timer is (as above) at 20. Since
the threshold of 50 will not be obtained for 10 more
seconds, the leading limit computation will want to set
the max timer to 10. Since the group max timer comp-
utation will only want to make it 5 (as in scenario 1), the
cycle leading limit’s value of 10 takes precedence. The
max timer will change its current value of 20 to 10.
TP GROUP WALK TIMINGS....Selection 4....
Range; 0-9.9 or 0-127 seconds
The TP walk group times operate similarly to the TP
max group times, including dynamic adjustment*.
These are typically set shorter than normal walk
(particularly for phases with long walk times) and will be
generally used to time out the phase walk quicker to get
to a transit priority phase. The group assignment to
cycle and split is the same as for TP Max groups, i.e. a
group assigned to a C/S combination pertains to both
max’s and walks. See TP group walk timing
computation during coordination below.
*TP group walk times with zero values will be
rejected relative to dynamic adjustment. That is, once a
walk has started normally, it cannot be adjusted to a
zero value, but will time out normally. Zero values for
walks that have not started, however, will be treated as
a form of ped omit and the walk will be skipped.
Note that Cycle Leading Limits should be employed
for CNA coord phases so that the transit priority
process will not initiate the release of hold too early (see
cycle leading limit programming).
Ped clear is not included in any TP groups because it
is not prudent to reduce ped clear times simply for
transit priority (TP is not pre-emption).
TP GROUP WALK TIMING COMPUTATION DURING
COORDINATION:
TP Group walk timing is straightforward, whether
coord or free, the walk is simply re-computed to reflect
the TP group time with no other considerations. When
cycle leading limits are applied for CNA coord phases,
however, walk may hold after the group walk time times
out. The CNA walk will then hold until the normal phase
force off point minus the cycle leading limit value. If this
threshold has already been surpassed when the group
walk time times out, the phase will immediately begin
ped clear.
Note: The hold duration described above is based on a
CNA coord phase force off value being judiciously
programmed. The correct placement of the CNA force
off point is at the desired release of walk point, which
can also be considered the desired end of phase green
minus ped clear.
TP FREE MODE
Back to the transit priority set-up menu...
TP FREE MODE....Selection 3....
This option determines how the Transit Priority will
operate when the unit is in free operation (no coord).
Mode = 0 The Transit priority process will select the
shortest of max 1 or max 2 for each phase when
attempting to shorten the phase to get to a transit
priority phase. Normal walk times only are used (no
walk reductions).
Mode = 1-3 The Transit priority process will select the
indicated group 1-3 when attempting to shorten the
phase to get to a transit priority phase. The selected
group applies to both the TP max time group and the TP
walk time group (e.g. group 1 = group 1 max’s and
group 1 walks). Program these accordingly
--TRANSIT PRIORITY MODE IN FREE OP—
MODE | 0 = USE SHORTEST OF MX1 OR
0 | MX2 & STANDARD WALKS
| 1-3 = USE MAX/WLK GP 1-3
PHASE 1 2 3 4 5 6 7 8
GP1 WLK 7 7 0 0 0 0 0 0
GP2 WLK 7 9 0 0 0 0 0 0
GP3 WLK 7 10 0 0 0 0 0 0
--TRANSIT PRIORITY SET-UP--
1. TP INPUT SET-UP 3. TP FREE MODE
2. TP GRP TIMING 4. TP COORD OPTIONS