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Subproblem 5a - Page 2 of 5 |
ID# C305A02 |
Sub-problem 5a:
Two-Phase Traffic Signal Control
Step 2: Results
The QEM represents an
extension of a technique known as Critical Movement Analysis, or CMA. This
technique has appeared in the literature in several forms and is intended
primarily for planning level analysis, though it is also very useful in both
operational and design reviews. The QEM produces an estimate of the
status of the overall intersection with respect to its capacity, based on
the assumption that the signal timing plan will produce an equal degree of
saturation among the critical movements on each phase. The intersection
status is determined from the sum of the v/c ratios for the critical
movements on each phase.
The QEM produces, as a by
product, a synthesized signal operating plan consisting of:
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A
phasing plan determined by the left turn treatments for each approach. The
left-turn treatments may be specified, or they may be synthesized, based
on the volumes of the left-turn movement and its opposing through
movement. |
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A cycle
length that will produce a target
v/c ratio of 90%. |
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An allocation
of phase times that will equalize the degree of saturation among the
critical movements on each phase. |
The HCM offers the caveat
that the synthesized plan may not be suitable for implementation because it
does not include important considerations such as minimum green times.
Nevertheless, it usually provides a good starting point for an operational
analysis, which requires the signal timing plan to be specified along with
several other items of geometric, operational, and traffic data that are not
always available at the planning level.
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