getting started 2

Chapter 15 tells us that an arterial analysis is performed separately on each segment of the facility. The only piece of facility-wide data is the length of the analysis period, usually 15 minutes or one hour. A segment is usually terminated by a signalized intersection. The following information is needed for each segment to produce an estimate of the LOS for a signalized arterial:

Exhibit 3-5. Information Required to Determine Arterial Level of Service
Data Item	Source or Assumptions
Segment length (usually the distance to the preceding intersection)	Scaled from map
Urban street Class (usually the same for all segments)	To be determined in Problem 1
Demand Volume	Based on traffic counts
Peak hour factor (PHF)	Based on field measurements
Free-flow speed	Set at posted speed + 5 mph
Cycle length	Based on field measurements. Different at each intersection because of isolated traffic-actuated operation.
g/c ratio	Based on field measurements
Arrival type	Always Arrival Type -3 because of isolated operation
Unit extension for traffic-actuated control	HCM default value of 3.0 sec will be used throughout.
Initial queue at the beginning of the analysis period	Assumed to be zero
Observed delay not related to the signal operation.	No other delays were observed.