Lec-8 Traffic Volume Counts and Road Accidents

Transportation Engineering - I

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

DemandCapacity

VolumeCongestion

Time

Tra

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Int

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Definitions

Volume

Time

Tra

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Int

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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

Day-to-day Variability of DailyProfile

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

30

K

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

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– 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-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

Automatic Count Study Preparation Checklist

Road Accidents

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.