Transcript Slide 1

Transportation Engineering - I
Lec-8 Traffic Volume Counts
and Road Accidents
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
Definitions
Traffic Intensity
Capacity
Demand
Volume
Congestion
Time
Definitions
Traffic Intensity
Volume
Time
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
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)
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
Counts in average
weekday in March,
recreational road,
in Minnesota,
March
Weekday ADT =
20,000 veh/day
AADT=?
Seasonal
and Weekly
Variability
of Daily
Volumes
AADT = 20,000∙(1/0.80) =
20,000∙1.25
AADT = 25,000 veh/day
1.25 = WF∙SF
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
4-5
8.5
5-6
10.6
6-7
6.0
Total
25.1
Wednesday ADT =
2,350∙(1/0.251) = 2,350∙3.98
= 9,360 veh/h
3.98 = 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
Day-to-day
Variability
of Daily
Profile
95% of
volumes
Within-Week
Variability of
Daily Flow
Composition
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 Definition
3
0
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)
Design Volume Estimation
Using Factor K
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
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–
–
–
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
Manual Traffic Count
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
Automatic Count Study Preparation
Checklist
Road Accidents
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.
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.
BThe 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 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
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.