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
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
Seasonal Variability of Monthly ADT
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)
128 %
WeeklyVariability
of Daily Volumes
Thursday daily traffic on a suburban arterial =
30,000 veh/day
Weekly ADT = ?
0.158
Weekly ADT ≈ Monthly ADT
= 30,000∙(1/0.158/7) == 30,000∙0.904 =Weekly ADT = 27,100 veh/day 0.904 = Weekly Factor (WF)
AADT = 20,000∙(1/0.80) = 20,000∙1.25
AADT = 25,000 veh/day
1.25 = WF∙SF
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=?
Vehicle counts on a local road on Wednesday between 4-7 PM gave total 2,350 vehicles
Wednesday ADT = ?
Daily Variability of Hourly Traffic
Counting Hour Percent of Daily Traffic4-5 8.55-6 10.66-7 6.0Total 25.1Wednesday ADT =2,350∙(1/0.251) = 2,350∙3.98= 9,360 veh/h3.98 = Daily Factor (DF)
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
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
AADT Estimation - Exercise• DF
DF = 1/(Proportion of Daily Traffic)DF = 1/(0.06+0.07) = 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∙
Design Volume Estimation Using Factor K
• 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)
DHV = AADT·K·D
Alternative Estimation of Design Volume
1. Estimate AADT1 for the year with available vehicle counts, AADT1=V∙DF1∙WF1∙SF1
2. Predict AADT2 for the future year using a growth factor AADT2=AADT1∙GF
3. Select month, day of week, and hour in the future year when the volume is likely to be close to the design volume
4. 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
Short-Term Volume
Variability
Traffic performance is checked for the worst 15 minutes of the design hour
Peak Hour Factor
Estimation of PHF
PHF = Hourly Count/(4·Highest 15-min Count)
Use of PHF
Peak Volume Rate = DHV/PHF
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)
Counting Techniques
• Manual 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.)
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
Origin-Destination Studies
• Internal (off the road)– Dwelling unit interviews– Vehicle owner mail questionnaires– Interview at traffic generators (workplace, etc)– Truck and taxi surveys
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-termcounts 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
DisasterDisaster
Webster’s Dictionary defines disaster Webster’s Dictionary defines disaster
as as
a baleful or fatal event leading to ruin.a baleful or fatal event leading to ruin.
•FamilyFamily
•CountryCountry
What’s more disastrous for someone What’s more disastrous for someone
than the death of a relative following a than the death of a relative following a
road traffic accident.road traffic accident.
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.
DESCRIPTIVE EPIDEMIOLOGY
Figure 2 : Road traffic injury mortality rates in the different regions of the world (1)
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
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)
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.
PREVENTION
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.
B- The key organizations intervening in the prevention
strategies :
Figure 7 : Organizations intervening in road safety actions(1)
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.
Measures avoiding road crashes, given an exposure
Speed limitationMeasures against « alcohol and driving »Measures avoiding the drivers fatigue :Measures ensuring pedestrian and cyclists
safetyPrevention of traffic accidents implying
young driversThe prohibition of the use of hand-held
mobile telephones while drivingMore road visibility
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
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 :
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.