Module 1: Traffic Engineering Studies

Question 1

Define mean.

Answer 1

Average

x = sum(xi) / n

x= average

n= sample of n observations

xi = sample values

If xi are rates, particularly crash rates or speeds from individual travel time runs, the previous equation will produce an incorrect answer. The true crash rate for n sections of roadway is found by dividing the total number of crashes on all n sections by the total travel on all sections.

Question 2

Define median value.

Answer 2

50th percentile value

Half of the sample observations are less than the median.

Question 3

Define mode.

Answer 3

The most frequently observed value of x.

In traffic studies it is often near the middle of the distribution.

Question 4

Define AADT

Answer 4

Average Annual Daily Traffic

Average 24 hour volume at a given location over a full 365-day year.

= every vehicle that passes a point during the year

365

Question 5

Define ADT

Answer 5

Average Daily Traffic

For a year is AADT can have ADT for a month, week, or for two days.

Must specify for what amount of time.

Question 6

Define AWT

Answer 6

Average Weekday Traffic

Average traffic between 12:01 AM on Monday to midnight on Friday.

Question 7

Define DHV

Answer 7

Design Hourly Volume

One hour volume (or flow rate) used as the basis of design or traffic operational decisions.

Typically 30th Highest Hour of the year

Question 8

How often to control count stations do traffic counts?

Answer 8

Control count stations do counts one week per month or one week per year.

Control = 1 Week

Question 9

How often to coverage count stations do traffic counts?

Answer 9

Coverage count stations count one day per year or one day per 2 to 4 years.

Coverage = 1 day

Question 10

How often do permanent count stations count traffic?

Answer 10

They count continuously. 24/7/365