Prof. Dr. Prof. Dr. PadmaPadma BahadurBahadur ShahiShahi

It is the process of estimating the number of vehicles ortravelers that will use a specific transportation facility inthe future.

A forecast estimates, for instance, the number of vehicleson a planned highway or bridge, the ridership on arailway line, the number of passengers patronizing anairport, or the number of ships calling on a seaport.

Traffic forecasting begins with the collection of data oncurrent traffic.Traffic forecasting begins with the collection of data oncurrent traffic.

Together with data on population, employment, triprates, travel costs, etc., traffic data are used to develop atraffic demand model.

Feeding data on future population, employment, etc.into the model results in output for future traffic,typically estimated for each segment of thetransportation infrastructure in question, e.g., eachroadway segment or each railway station.

ForecastingTechniques

QualitativeModels

Time SeriesMethods

DelphiMethod

Jury of ExecutiveOpinion

Sales ForceComposite

NaiveMovingAverage

WeightedMoving Average

CausalMethods

CompositeConsumer Market

SurveyExponentialSmoothing

Trend Analysis

SeasonalityAnalysisSimple

Regression

MultipleRegression

MultiplicativeDecomposition

Qualitative incorporatesjudgmental & subjective factors intoforecast.

Time-Series attempts to predict the Time-Series attempts to predict thefuture by using historical data.

Causal (contributory) incorporatesfactors that may influence thequantity being forecasted into themodel

Traffic forecasts are used for several key purposes intransportation policy, planning, and engineering: tocalculate the capacity of infrastructure, e.g., howmany lanes a bridge should have; to estimate thefinancial and social viability of projects, e.g., usingfinancial and social viability of projects, e.g., usingcost-benefit analysis and Social impact analysis; andto calculate environmental assessment, e.g., airpollution and noise.

Within the rational planning framework,transportation forecasts have traditionally followedthe sequential four-step model or urbantransportation planning (UTP) procedure.

Typically, forecasts are made for the region as a Typically, forecasts are made for the region as awhole, e.g., of population growth. Such forecastsprovide control totals for the local land use analysis.Typically, the region is divided into zones and bytrend or regression analysis, the population andemployment are determined for each

jiTrip generation

i jTrip Distribution

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Dr. P. B. Shahi 22

ji Modal Split

Tij auto

Tij transit

Traffic Assignment

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route network

Trip Generation: determines the frequency oforigins or destinations of trips in each zone by trippurpose, as a function of land uses and householddemographics, and other socio-economic factors.Trip distribution: matches origins withdestinations, often using a gravity model function.destinations, often using a gravity model function.Modal Split model: computes the proportion oftrips between each origin and destination that use aparticular transportation mode. This model is oftenof the logit form.Traffic Assignment models: allocates tripsbetween an origin and destination by a particularmode to a route.

Vehicle Classification

AADT & ADT

Manual: 24 hour count: classified count

Continuous count:

Automatic devices (sensors) Automatic devices (sensors)

Traffic counts carried out over a very short timeperiod can produce large errors because traffic flowshave large hourly, daily, weekly, monthly andseasonal variations.

Hourly Variation: Hourly Variation:

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12 hours count (6-18 hrs): 80% of days traffic

16 hours count (6-22 hours): 90% of days traffic

Week days & holidays trip rates are different

Always avoid holidays traffic count for data analysis

Whole week count may confirm the daily variation

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Traffic Count Survey

Result of Classified manual count

Date: 2067/1/12 Location:Near Lahan bazar (west 500m)

Road Link: EW Highway, at Lahan Station:

Name of Road: Belbari Chauharwa (B-C) Surveyed by: Manoj Prajapati

Seasonal Variation Factor: 0.85 Supervised by:Firoj Shrestha

Start Time

Motorized Vehicle Non Motorized

Total

Truck Bus

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a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b a b (a+b)

06:00 - 18:00 24 19 77 81 16 19 96 83 41 40 112 108 90 82 16 16 42 59 52 52 4 1 625 594 18 8 38 38 857 888 2108 2088 419618:00 - 06:00 41 40 46 39 10 3 103 60 12 5 16 13 17 21 8 5 6 7 31 31 3 0 87 134 11 2 7 9 187 169 585 538 1123Sub-Total 65 59 123 120 26 22 199 143 53 45 128 121 107 103 24 21 48 66 83 83 7 1 712 728 29 10 45 47 1044 1057 2693 2626 5321

Total (a+b) 124 243 48 342 98 249 210 45 114 166 8 1440 39 92 2101 5319

Composition, % 2.3 4.6 0.9 6.4 1.8 4.7 3.9 0.8 2.1 3.1 0.2 27.1 0.7 1.7 39.5 100

PCU Factors 4 3 1.5 3 2.5 1.5 1 1 0.75 1.5 1.5 1.5 8 1 0.5

PCU, ADT496 729 72 1026 245 374 210 45 86 249 12 2160 312 92 1051 7158

AADT, PCU 422 620 61 872 208 317 179 38 73 212 10 1836 265 78 893 6084

Nor carrying out Classified count

Not distinguishing two-way & One-way traffic data

Not distinguishing between directions in trafficcount

Incase of automatic count : axle count and vehicle Incase of automatic count : axle count and vehiclecount

Converting a partial-day counting to a full-day count

Essential for pavement design

Volume can be found by traffic count and Vehicleload is found by axle load survey.

It is carried out to determine the axle loaddistribution of heavy vehicles using road.distribution of heavy vehicles using road.

These data are then used to calculate the meannumber of equivalent axles for atypical vehicle class.

If flow is too high sampling will need to be selectedfor weighing.

All vehicles need not to be weighed. (less than 1.5tonnes.

Methods:

Fixed weigh bridge

Portable weigh pads

Weigh in Motion

New Expensive Technology less accuracy

Brief classified count must be carried out in advancethe axle load survey

At least 12 hours axle load survey covering 80%vehicles.

Sampling Sampling

Up to 60 heavy vehicles per hour: all

61 to 120 alternate vehicles

121 to 180 one in three

181 to 240 one in four

Road CONNECTIVITY SECTOR 1 PROJECT

Axle Load survey

Road: Location: Survey Period/Duration:Road: Location: Survey Period/Duration:

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Front Rear 1 Rear 2 Rear 3 Rear 4

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axle load analysis.xls

5.4

16.8

=

AxleloadEF

Rear axle dual wheel

16.8 Front axle single wheel

5.4

41.5

=

AxleloadEF

Standard axle load of 8.16 ton will have an EF=1

The axle load of 16.32 ton will have EF=22.6

This means doubling the axle load will not simplydouble the damaging effect but it will increase it byover 22 times.over 22 times.

Growth factor:

r is annual growth rate

n is number of design year

Total cumulative Equivalent Single Axle:

r

rGFn 1)1( +

=