2D. Traffic analysis

Question 1

What are the 3 levels of analysis defined by the HCM

Answer 1

HCM: Volume 1 - Chapter 2

Operational analysis:
Typically focuses on current or near-term conditions. It involves detailed inputs to HCM procedures, with no or minimal use of default values.

Design analysis:
Typically uses HCM procedures to identify the characteristics of a transportation facility that will allow it to operate at a desired LOS, with some use of default values.

Planning and preliminary engineering analyses:
typically focus on initial problem identification, long-range analyses, and performance monitoring applications, where many facilities or alternatives must be evaluated quickly or when specific input values to procedures are not known. The extensive use of default values is required.

Question 2

What is a peak hour factor?

Answer 2

PE. Handbook 5.1.3.3

PHF = V / (V15*4)

Where
PHF =peak­ hour factor
V = hourly volume for hour of analysis
V15 =maximum 15­min flow rate within peak hour

The hourly volume should be the highest number of cars within a 1 hour time range.

Question 3

If Peak hour volumes are not given what number should be used

Answer 3

0.85 for Rural areas
0.90-0.95 for suburban/urban areas

Question 4

How to calculate DDHV

Answer 4

DDHV = = AADT x K x D
AADT is the average annual daily traffic
K is the proportion of daily traffic occurring at peak hour
D is the directional distribution (decimal)

D is typically shown as 60/40 for the peak direction

Question 5

How to calculate heavy vehicle adjustment factor

Answer 5

Fhv = V(vph) / V (pce)

Fhv = heavy vehicle adjustment factor
V(vph) = volume in vehicles per hour
V(pce) = passenger equivalent cars

Results should be less than 1

Question 6

How to calculate a speed limit from the 85th percentile

Answer 6

85th percentile can be found by:
Taking the cumulative total of all the cars.
Multiply by 0.85
Determine the speed at the resulting number
Round speed to the nearest 5mph