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Sub-problem 4a - Page 1 of 4

ID# C404A01

Sub-problem 4a: Division of Alternate Route 7 for Analysis

Step 1. Set-up

The freeway facilities procedure (as documented in Chapter 22 of the HCM) uses component procedures (basic freeway segments, weaving sections, and ramp junctions) from three HCM chapters (23, 24, and 25) in an integrated manner to produce an assessment of the performance of the facility as a whole. The purpose of this sub-problem is to provide you with the experience of determining the appropriate segments for such an analysis. That is, how must we divide up the facility into manageable parts that will allow us to conduct an operational analysis using the methods of the HCM?

We need to divide the facility into both temporal and spatial segments. The time segments are usually the 15-minute time blocks typically used in an HCM analysis. The freeway is also divided into spatial segments whenever there is a change in the demand (because of an on-ramp or off-ramp) or capacity (number of lanes, grade change, etc). We further divide the segments into sections noting each of the standard HCM analysis procedures relevant to a section: basic section, ramp influence area, and weaving section. For example, consider a section of freeway, 5,000 feet in length, bounded by an on-ramp and an off-ramp. The section would be divided into a merge influence area 1,500 feet in length, a basic freeway segment 2,000 feet in length, and a diverge influence area 1,500 feet in length.

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