1. Chapter 1 Traffic Flow What you will be learning from this chapter …
TRAFFIC STUDIES
Traffic Volume
Spot Speed
TRAFFIC FLOW THEORY
Traffic Flow Parameters
Speed, Flow & Density Relationship
CAPACITY & LEVEL OF SERVICE
Multilane Highway Capacity Study

2. TRAFFIC STUDIES May grouped into
Inventories – existing information that related to street width, parking space, transit routes, traffic regulation etc.
Administrative studies – existing engineering record. Eg. Result of survey (field measurements)
Dynamic studies – study on current operational condition. Eg. Speed, traffic volume, travel time etc.

3. TRAFFIC VOLUME STUDY Traffic volume is ......
the number of vehicles passing a given point during a specified period of time. (The time is varies from as little as 15 minutes)
Data collected may be put into subclasses such as:
Directional movement
Occupancy rates
Vehicle classification
Pedestrian age
Traffic volume studies are usually conducted when certain volume characteristics are needed such as:
Average Annual daily Traffic (AADT) – average of 24-hr counts collected everyday of the year. It used for
Estimation of highway user revenues
Computation of crash rates in terms of number of crashes per 100 million vehicle miles

4. Average Annual daily Traffic (AADT) – average of 24-hr counts collected everyday of the year. It used for
Estimation of highway user revenues
Computation of crash rates in terms of number of crashes per 100 million vehicle miles
Establishment of traffic volume trends
Evaluate the economic feasibility of highway projects
Develop freeway & major arterial street systems
Develop improvement & maintenance programs
Average Daily Traffic (ADT) – average 24-hr counts collected over a number of days greater than one but less than a year. It used for:
Plan highway activities
Measure current demand
Evaluate existing flow
Peak Hour Volume (PHV) - maximum number of vehicles that pass a point on a highway during a period of 60 consecutive minutes . Used for:
Functional classification highway
Design geometric of highway (lane, lane width, shoulder etc)
Capacity analysis
Parking regulation

5. Vehicle classification (VC) – records volume based on type of vehicle
Vehicle classification (VC) – records volume based on type of vehicle. Eg. car, motorcycle, truck etc. It used for
Design the road geometric with particular reference to turning-radii, max. grades, lane widths etc.
Capacity analysis with respect to passenger-car-equivalents of trucks
Adjust traffic count obtained by mechine
Structural design of highway pavements, bridge etc.
Classification counts should be conducted if:
the percentage of heavy trucks is high
vehicle mix at crash site is acontributing factor to the crash problem
Vehicle Miles of Travel (VMT) – measure of travel along a section of road

6. The importance of traffic volume study ......
For traffic planning, design & research.
To determine the efficiency of a traffic system.
To evaluate the quality of service of a transport facility.
To design roads – number of lanes & pavement thickness.
Volume study methods
Manual Count Methods
Automatic Count Methods

7. METHOD OF CONDUCTING VOLUME COUNTS
2 Basic method:
Manual method
involve 2 – 3 persons recording the number of vehicles using counter
applicable for vehicle volume studies at intersection
Automatic method
uses an automatic counter
those that require surface/subsurface laying counter detector. eg. pneumatic road tubes or magnatic counter
those do not require laying detector

8. Counting periods
The time and length that a specific location should be counted is also dependent upon the data desired and the application in which the data are to be used
24-hour counts (24-hour period between noon Monday and noon Friday).
16-hour counts from 6 a.m. to 10 p.m. This period contains most of the daily flow including evening traffic.
12-hour counts (from 7 a.m. to 7 p.m. to cover most daytime traffic movements, especially in commercial or business areas. Such counts made in shopping centers or districts where stores are open at night are usually extended until after 9 p.m).
Peak-period counts which vary depending upon size of metropolitan area, proximity to major generators (such as the CBD or industrial areas), and the type of the facility (gateway, radial arterial, etc.). Commonly used periods are 7 to 9 am and 4 to 6 p.m.

9. Counting periods
Special conditions should be avoided unless the purpose of the count is to obtain data concerning these unusual conditions. Examples of such conditions include:
Special events (holidays, sports, exhibitions, sales., etc).
Abnormal weather conditions which do not generally occur.
Temporary closure of streets effecting the volume pattern.
Transit or trucking strikes.

10. MANUAL COUNT Manual Count method ......
BFC3082 Traffic and Road Safety Engineering Lecturer: Mr. Basil David Daniel
MANUAL COUNT
Manual Count method
Applied when small sample of data is required.
For periods less than one (1) day.
Normal intervals are 5, 10 or 15 minutes.
Counts are not usually taken on Mondays, Fridays and weekends.
Can anyone explain why ?
Manual Count recording methods
Tally Sheets
Mechanical Counting Boards
Electronic Counting Boards

11. MANUAL COUNT Manual counting board Tally sheet
Electronic counting board

12. AUTOMATIC COUNT Automatic Count method ......
Applied when large sample of data is required.
For periods more than one (1) day.
Normal intervals are 1 hour for a 24 hour period.
Counts may extend to a week, month or year.
Automatic Count recording methods
Portable Counters
Permanent Counters
Videotape

13. AUTOMATIC COUNT PORTABLE COUNTERS
Traxmite Pneumatic Road Tube & Recorder
Hi-Star Portable Traffic Counter
PERMANENT COUNTERS
Loop Detector

14. SPOT SPEED STUDY

15. What is a Spot Speed Study?
Spot speed studies are used to determine the speed characteristics of a traffic stream at a specific location along the roadway.

16. Why Spot Speed Studies? Determine existing roadway speeds
Evaluate effectiveness of speed enforcement programs
Identify the speed impact of roadway geometry and roadway features
Determine impact on speed of traffic control devices
Provide evidence to support/refute excessive speed complaints

17. SPOT SPEED STUDY Spot speed study ......
A study of speed of traffic at one point or spot on a trafficway.
Consists of a series or sample of observations of individual speeds of vehicles approaching an intersection or passing a point at a non-intersection.
Used to estimate the speed distribution of an entire traffic stream at that location under prevailing traffic conditions.
Spot speed studies are carried out at
Trend locations – straight, level, open sections of rural highways, and midblock at urban streets.
Problem locations – accident blackspots, and locations where traffic signals and signs are contemplated.
Representative locations – for basic data surveys.
Locations of before-and-after studies.

18. Spot Speed Study Steps STEP 1 --- Organize Study Plan
STEP Select Data Collection Technology
STEP Select Appropriate Site and Collect Field Data
STEP Reduce and Analyze Data
STEP Interpret and Report Findings

19. STEP 1. Organize Study Plan
Reason for Study
Identify Problem
Plan Logistics
Select Date and Time
Select Location
Number of Vehicles to Observe

20. Time and Date Selection Recommended - Reflect normal driving conditions
Late spring or early autumn
Tuesday, Wednesday or Thursday
Not Recommended:
Unique events
Inclement weather
Holidays
Peak travel times

21. Location Selection - Reflect normal driving
Recommended:
Free flow conditions
Uniform roadway segments
Not Recommended:
Traffic signals and other junctions
Intersections
Curves
Work zones
Parking zones
Active crosswalks

22. STEP 2. Select Data Technology

23. STEP 2. Select Data Technology

24. Handheld Technologies
Handheld radar or LiDARmeters to identify vehicle speeds
Speeds are recorded manually on a data sheet
Minimum data requirements must be met to ensure quality of data
Efforts must be made to reduce bias

25. In-Road Technologies
Disruption of traffic flow during installation and maintenance
Safety concerns for operating in the road
Maintenance issues:
Snow removal, street sweepers, flood etc.
Heavy vehicle traffic
Typically well established technologies

26. Out-of-Road Technologies

27. STEP 3. Collect Field Data

28. STEP 3. Collect Field Data

29. Additional Safety Considerations

30. STEP 3. Collect Field Data

31. STEP 4. Reduce and Analyze Data

32. SPOT SPEED STUDY
STOPWATCH METHOD

33. SPOT SPEED STUDY
RADAR METER METHOD

34. SPOT SPEED STUDY PNEUMATIC ROAD TUBE METHOD Recorder
Pneumatic Road Tubes

35. ANALYSIS OF SPOT SPEED DATA
Spot speed data can be presented as:
frequency distribution table.
frequency and cumulative frequency distribution curve
common descriptive statistics
The mean speed
The median speed
The pace
the standard deviation
the 85th and 15th percentile speeds