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Sub-problem 3c - Page 2 of 4

ID# C103C02

Sub-problem 3c: Critical movement analysis

What is critical movement analysis? Critical movement analysis is a method to determine whether the projected volumes at a signalized intersection will be under, near, or over the intersection's capacity to accommodate them. The method is fully documented as a planning-level procedure in Transportation Research Circular 212. The method considers each of the four conflicting movement pairs at the intersection (for example, the NB LT and the SB TH movements). The critical movements for each intersection phase (for example, the maximum of either the NB LT/SB TH movement and the SB LT/NB TH movement) are summed. This sum is compared with the following standards:

Exhibit 1-36. Intersection Performance Assessment by Critical Volume
Sum of Critical Volumes (v/hr) Intersection Performance Assessment
0-1,200 Under capacity
1,201 - 1,400 Near capacity
1,401 and above Over capacity

What data are needed to conduct critical movement analysis? The approach volumes, the number of lanes, and the lane configuration on each approach are the data needed to conduct a critical movement analysis.

What outputs are produced by critical movement analysis? Critical movement analysis produces only an assessment of the intersection's sufficiency to accommodate the projected volumes. It does NOT provide estimates of delay, LOS, or queue lengths.

Are the results from critical movement analysis any more or less valid than the results produced by the HCM or by microscopic simulation models? The results of a critical movement analysis help to determine whether the intersection will operate under, near, or over capacity. It is more of an approximation than either the HCM or other models, but in many cases the results from a critical movement analysis are sufficient to answer the question at hand.

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