1. Lec-8 Traffic Volume Counts and Road Accidents
Transportation Engineering - I
Lec-8 Traffic Volume Counts and Road Accidents

2. Definitions
Count – number of vehicles/travelers passing a highway spot in a counting period
Volume – number of vehicles/ travelers passing a highway spot per unit time
Capacity – maximum and repeatable volume of vehicles/travelers
Demand – volume not influenced by highway capacity

3. Definitions
Capacity
Demand
Traffic Intensity
Volume
Congestion
Time

4. Definitions
Volume
Traffic Intensity
Time

5. AADT vs. ADT AADT = Annual Average Daily Traffic (veh/day)
ADT = Average Daily Traffic (veh/day) represents periods other than a year
Weekly ADT, Monthly ADT

6. Seasonal Variability of Monthly ADT
128 %
Counts in August on a rural road have given August Monthly ADT = 10,000 veh/h
What is Annual ADT?
AADT = 10,000∙(1/1.28)
=10,000∙0.781
AADT = 7,810 veh/day
0.781 = Seasonal Factor (SF)

7. Weekly Variability of Daily Volumes
0.158
Thursday daily traffic on a suburban arterial =
30,000 veh/day
Weekly ADT = ?
= 30,000∙(1/0.158/7) =
= 30,000∙0.904 =
Weekly ADT = 27,100 veh/day
0.904 = Weekly Factor (WF)
Weekly ADT ≈ Monthly ADT

8. Seasonal and Weekly Variability of Daily Volumes
Counts in average weekday in March, recreational road, in Minnesota,
March
Weekday ADT =
20,000 veh/day
AADT=?
AADT = 20,000∙(1/0.80) = 20,000∙1.25
AADT = 25,000 veh/day
1.25 = WF∙SF

9. Daily Variability of Hourly Traffic
Vehicle counts on a local road on Wednesday between 4-7 PM gave total 2,350 vehicles
Wednesday ADT = ?
Counting Hour Percent of Daily Traffic
Total
Wednesday ADT =
2,350∙(1/0.251) = 2,350∙3.98
= 9,360 veh/h
3.98 = Daily Factor (DF)

10. AADT Estimation with Short Counts
AADT = V·DF·WF∙SF
where:
AADT = Annual Average Daily Traffic,
V = count in veh,
DF = Daily Factor,
WF = Weekly Factor,
SF = Seasonal Factor,
More than one day of counting (three days) and extended count periods each day are recommended

11. Day-to-day Variability of Daily Profile
95% of volumes

12. Within-Week Variability of Daily Flow Composition

13. AADT Estimation - Exercise
Vehicle counts have been conducted in mid March on Thursday between 3 and 5 PM.
Known:
Total count V=2,000 veh,
Volume between 3 and 4 PM equals 6 % of daily traffic
Volume between 4 and 5 PM equals 7 % of daily traffic
Thursday daily traffic equals 16 % of weekly traffic
March daily traffic equals 98 % of AADT
Calculate
Daily Factor DF
Weekly Factor WF
Seasonal Factor SF
AADT

14. AADT Estimation - ExerciseDF
DF = 1/(Proportion of Daily Traffic)
DF = 1/( ) = 7.69 WF
WF = 1/(Proportion of Weekly Traffic)/7
WF = 1/0.16/7 = 0.89 SF
SF = 1/(Proportion of AADT)
SF = 1/0.98 = 1.02
AADT
AADT = V·DF·WF∙SF
V = 2,000 vehicles
AADT = 2,000∙7.69·0.89·1.02 = 13,800 veh/day

15. Design Volume DefinitionK 30

16. Design Volume Estimation Using Factor K
DHV = AADT·K·D
AADT in the horizon year (veh/day)
K = proportion of AADT during the 30th rank hour (other ranks may be used too)
D = directional split (busier direction)

17. Design Volume Estimation Using Factor K

18. Alternative Estimation of Design Volume
Estimate AADT1 for the year with available vehicle counts, AADT1=V∙DF1∙WF1∙SF1
Predict AADT2 for the future year using a growth factor AADT2=AADT1∙GF
Select month, day of week, and hour in the future year when the volume is likely to be close to the design volume
Convert the predicted AADT2 to the hourly volume for the hour selected in step 3, DHV=AADT2/DF2/WF2/SF2
or DHV = V ∙ (DF1/DF2) ∙ (WF1/WF2) ∙ (SF1/SF2) ∙ GF

19. Short-Term Volume Variability
Traffic performance is checked for the worst 15 minutes of the design hour

20. Peak Hour Factor Estimation of PHF
PHF = Hourly Count/(4·Highest 15-min Count)
Use of PHF
Peak Volume Rate = DHV/PHF

21. Types of Volume Studies
Intersection counts (duration depends on the purpose, 15-minute intervals or shorter, turning volumes)
Pedestrian counts (duration depends on the purpose, 5-minute intervals or longer)
Cordon counts (one weekday + travelers’ survey)
Screen line counts (hourly counts for a weekday)
Area wide counts
Control counts (hourly counts with permanent stations)
Coverage counts (hourly counts for one or two days)

22. Counting Techniques Manual counting Machine counting
For one day or less
Turning volumes, pedestrians, test counts
Pencil and paper
Electronic manual recorders
Machine counting
For longer counting periods: one day or longer
Permanent stations (inductive loops, WIM)
Portable stations (pneumatic, inductive, magnetic, video, etc.)

23. Origin-Destination Studies
External (on the road)
Cordon studies
Roadside interviews
Postcard studies
License plate studies
Tag-on vehicle method
Lights-on studies
Transit passenger questionnaire

24. Origin-Destination Studies
Internal (off the road)
Dwelling unit interviews
Vehicle owner mail questionnaires
Interview at traffic generators (workplace, etc)
Truck and taxi surveys

26. Manual Traffic Count

28. Automatic Count Recording Methods
Automatic counts are recorded using one of three methods: portable counters, permanent counters, and videotape.
Portable counters serve the same purpose as manual counts but with automatic counting equipment.
The period of data collection using this method is usually longer than when using manual counts. The portable counter method is mainly used for 24-hour counts.
Pneumatic road tubes are used to conduct this method of automatic counts.
Permanent Counters
Permanent counters are used when long-term
counts are to be conducted.
The counts could be performed every day for a year or more.
Videotape
Observers can record count data by videotaping traffic. Traffic volumes can be counted by viewing videotapes recorded with a camera at a collection site

29. Automatic Count Study Preparation Checklist

30. Road Accidents

31. Disaster Webster’s Dictionary defines disaster as
a baleful or fatal event leading to ruin.
Family
Country
What’s more disastrous for someone than the death of a relative following a road traffic accident.

32. INTRODUCTION
Injuries account for 12% of the global burden of disease (1, 2)
Traffic accidents are costing countries between 1% to 2 % of their gross national product
Traffic accidents are a major preventable public health problem
About 1,2 millions persons were killed and 50 millions were injured, worldwide, in 2002.

33. DESCRIPTIVE EPIDEMIOLOGY
Figure 2 : Road traffic injury mortality rates in the different regions of the world (1)

34. DESCRIPTIVE EPIDEMIOLOGY
Worldwide
Road traffic injuries mortality rates :
* 1,2 millions persons killed every year
* 3242 persons killed every day
* Traffic accidents : 11th cause of death
* Developing countries:
- 2/3 of the world population
- 90% of deaths due to road crashes

35. DESCRIPTIVE EPIDEMIOLOGY
Worldwide
Road traffic injury mortality rates :
* Increase in the mortality rates of 10% between 1990 and 2002 (1)
* Differences between developped and developing countries
Figure 3 : Changes in road crashes mortality rates according to countries (1)

36. RISK FACTORS The risk depends on four elements :
A)   Exposure excess (need to travel)
B)   Risk of crash, given a particular exposure,
C)   Risk of injury, given a crash,
D)   Risk of death or severe consequences, given an injury.

37. PREVENTION Taffic accidents are preventable.
Taffic accidents are preventable.
The three targets of the road safety actions :
- the road users
- the vehicles
- the roads infrastructure as well as the traffic management.

38. B- The key organizations intervening in the prevention strategies :
Figure 7 : Organizations intervening
in road safety actions(1)

39. C- Prevention measures :
Prevention strategies are made of interventions which are aiming to :
diminish the exposure risk.
avoid road crashes, given a particular exposure.
reduce the severity of injuries caused by crashes
improve the medical care for victims.

40. Measures avoiding road crashes, given an exposure
Speed limitation
Measures against « alcohol and driving »
Measures avoiding the drivers fatigue :
Measures ensuring pedestrian and cyclists safety
Prevention of traffic accidents implying young drivers
The prohibition of the use of hand-held mobile telephones while driving
More road visibility

41. a – The use of seat-belts
Measures reducing the severity of injuries caused by crashes :
a – The use of seat-belts 
When used, the seat-belt reduce the risk of fatal or severe accident, between 40% and 65 % (1).
Making the wearing of safety belts compulsory improves their use rates.
b- Use of helmets 
c- Availability of air bags

42. Actions improving post-crash injury outcome 
- pre-hospital mesures :
* Bystanders : call for help, carry out simple acts to rescue victims, protect victims from an other accident
* Larger access to emergency services
* Better pre-hospital medical care
- actions in the hospital :

43. CONCLUSION
Traffic accidents constitute a huge public health problem: a man made disaster.
The situation is going to be worse unless prevention strategies are adopted.
There is a hope to avoid such losses of lives, of health and of money by setting road safety actions.
A scientific approach to the issue is essential in every country, so that road safety policies could be founded on reliable data, and meeting financial resources of each region.