Traffic Count Methodology

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Traffic Count Methodology

Introduction

The annual traffic count report contain summary data of 24 Hr. traffic counts and P.M.. peak-hour directional counts for various locations in Orange County for the year 1994 and 1995. The traffic count data is listed alphabetically and is listed in order North to South and West to East. For example, traffic on Orange Blossom Trail begins north of Saddler Road and ends north of the Orange County line.

Methodology

The data for this report is collected and analyzed by the Orange County Traffic Engineering Division using mechanical counters that record the distribution of traffic by time of day, 3-day (Tuesday-Thursday). The data is summarized to show the Average Daily Traffic (ADT) and average weekday characteristic by traffic station.

Data Uses

The traffic count information is extremely important to traffic planning, design, and operations. This data is regularly requested by developers, consultants, real estate agents, home owners associations, speculators, government agencies, and citizens.

Definition of Terms

Average Daily Traffic
The total volume passing a point or segment of a road facility, in both directions, during a 24-hour period. It is commonly obtained during a given time period, in whole days greater than one day and less than one year, divided by the number of days in that time period. Usually abbreviate ADT.

D or Directional Distribution Factor
This factor accounts for the directional distribution of traffic. Values generally range from .54 to .59 and are used to convert average daily traffic to directional peak hour traffic. Table 1 illustrates how the D-factor is calculated:

Table 1 - Estimated D

Measured Day	Peak Hour	Peak Hour Volume	Predominate Direction Peak Volume	Opposite Direction Peak Volume	D Factor
1/18	4-5 pm	1600	960	640	0.600
1/19	5-6 pm	1900	1026	874	0.540
1/20	5-6 pm	2000	1130	870	0.565
Sum		5500	3116	2384	1.703
Average		1833	1039	795	0.568
Estimated D Factor = 0.568

K or Design Hour Factor
The ratio of design hour traffic to average annual daily traffic. The K-100 factor allows the conversion from a peak hour volume to a daily volume. Within urbanized areas the K- factor for the 100th hour is generally around 0.09. Table 2 is an example of a K-100 calculation:

Table 2 - Calculating K

Measured Day	Peak Hour	Peak Hour Volume	Daily Volume	Peak To Daily Ratio
1/18	4-5 pm	1600	20000	.080
1/19	5-6 pm	1900	25000	.076
1/20	5-6 pm	2000	22000	.091
Average			22333	.082
Peak Daily Volume / Average Daily Volume = 25000 / 22333 = 1.119
ESTIMATED K FACTOR = .082 X 1.119 = .092

P.M. Peak Directional Peak
The traffic volume for the peak hour in the predominant direction of flow, in vehicles per hour. PM DIR PEAK = (ADT) (K-100) (D-FACTOR)

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