Economic impact of traffic congestion- estimation and challenges

Abstract

Traffic congestion has become a critical concern when its detrimental effects are taken into account. Incremental delay, excessive fuel consumption and higher vehicle emission are thoughtful impacts of traffic congestion. These negative impacts cause substantial economic losses to the transport system. Hence, it is essential to enumerate these impacts in their monetary terms to provide a better economic growth and social welfare to the society. Thus, a comprehensive review on the impact of traffic congestion comprises traffic delay, fuel consumption and vehicle emission has carried out. Moreover, the paper reviews the economic quantification of this three impacts of traffic congestion. Systematic understanding and estimation are possible by the support of empirical data. Hence, this paper discusses the data requirements and data collection methods for the estimation of delay cost, fuel cost and emission cost. A new methodology has proposed to estimate delay cost for the link, intersection and corridor as separate facilities. This paper also focuses on the challenges to be confronted while quantifying the congestion impacts in monetary value and further research direction are proposed. © 2018 Institute for Transport Studies in the European Economic Integration. All Rights Reserved.

Full text

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European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
2
movements. Congestion adversely affects the economy and social well-being of the road
users by wastage of time, deterioration of the health, travel time delay, inability to
forecast travel time, increased fuel consumption which causes air pollution and gas
emission, wear and tear on vehicles, noise pollution and reduction in road safety.
When the transportation system collapses to the condition of traffic congestion from the
normal condition, the financial planning of the transport system increases because it has
to provide mitigation measures such as widening of roads and construction of fly overs
for the smooth flow of traffic. Congestion leads to an economic inflation, referred as an
inconvenience and incremental cost resulting from the interference among road users
(Litman, 2013). Traffic congestion costs constitute both internal and external parameters
in which internal or direct cost is induced by vehicle users while the congested
surroundings generate an external or social cost. Direct cost is borne by the non-
productive activity of road users and extraneous consumption of fuel. Likewise, the
social cost is brought about by external elements in transport system such as air and
noise pollution, accidents and risk from accidents and imposes society as
whole.(Thomson & Bull, 2002).
The review of literatures related to the above subjects reveals that many analyses have
been performed to establish the cost of traffic congestion. Many conventional works
deal with different types of congestion estimation methods such as total cost, marginal
cost and excess burden cost (OECD Transport Research Centre, 2007).Researchers also
recognized the agglomeration externalities to estimate the traffic congestion cost. The
agglomeration externalities concentrates on the estimation of economic activity in the
area and thus by providing different policies to mitigate traffic congestion.(Arnott,
2007).Though, various investigations have been carried out to examine the cost of
congestion, only limited number of studies were made to quantify the economic impact
of traffic congestion. However, this review proposes a framework for emphasizing the
three important impacts of traffic congestion and its economic estimation.
A challenge to transport investors and planners is to mitigate traffic congestion and thus
provide a better economic growth and social welfare to the society. For this, congestion
impacts have to be estimated on their monetary terms. Hence, a comprehensive review
concentrates on three important impacts of traffic congestion namely delay impact, fuel
consumption impact and emission impact. Furthermore, a systematic review of data
requirements and data collection methodology is addressed in this paper. A new
methodology has been proposed to estimate delay cost for the link, intersection and
corridor as separate facilities. The heterogeneity in vehicle and location characteristics
made the cost evaluation technique unique for various countries. Moreover, the
challenges to be addressed while quantifying the congestion impacts and further
research direction are presented in this paper.
2. Evaluation Of Congestion Impacts
The general methodology that has been followed in many studies for the congestion cost
estimation is depicted in the Fig.1. In view of this framework, the three main impacts
are considered. Primarily, the discussion of the congestion impact on traffic delay is
considered and delay cost is estimated by means of the value of travel time. A method

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European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
5
intersections. A major disadvantage of this method is the prolonged duration which
causes undue strain on the observers. In order to overcome that, video graphic method
can be used.
In video graphic method, high resolution video cameras are placed at two ends of the
section by synchronizing the time and record video to obtain the travel time. By
replaying the recorded video and noting down the time taken to the entry and exit time
of the vehicle in the section. This method has an advantage over the registration number
method because it can capture different vehicle type data accurately with less
manpower. In congested state vehicle occupies on the road fully, video graphic method
provides more accurate data than registration number method.
In floating car method, global positioning system (GPS) and distance measuring
instruments (DMI) can be fitted in the vehicle to obtain travel time and it will give
microscopic features of a travel time component. The manual method using stopwatches
in the floating car survey is also a tool for travel time data collection. For congestion
prevailing under homogeneous conditions floating car method gives the best results and
where as in heterogeneous conditions, several runs have to be taken for different vehicle
types to get accurate data.
Time is an economic commodity, and it helps to accomplish products and services as
valuable items. Generally, travellers prefer to choose the route of less travel time, even
at long distance and high running cost of the vehicle. Since travel time has a value, but
the value of travel time depends on many factors, each of varying importance depending
upon the traveller, the purpose of travel, the amount of time available, the reliability of
having the time to use etc. Hence, data collection should include the factors affecting
their travel journey of different rod users.
Wage rate approach and preference approach are the two distinct approaches in the
economic evaluation of travel time. The common and simple approach to ascertain the
passengers travel time cost is to evaluate the average wage rate of the road user and to
treat it as the time value of his travel. As the trip characteristics changes from work time
journey and leisure time journey, the value of travel time for trips also may vary. A
major disadvantage of the wage rate approach is that, it does not account the trip
characteristics of the passengers and is difficult to find the travel time value for
unemployed road users. Hence, preference survey helps to find the distinct behaviour
and value of travel time for different trips.
In preference survey approach, the travellers are asked to value the price they would pay
for reduced travel durations. The actual rating of travellers would depend upon their
wage rate, personal choice, trip characteristics and purpose of the trip. This include
revealed preference (RP) and stated preference approach (SP) and it is the most
scientific way to estimate the value of travel time .Value of travel time is defined as the
ratio of the marginal utility of travel time over the travel cost. It is done by studying the
choice of people and their preference to reduce travel time and travel cost (Beshears et
al 2008). The RP approach evaluate value of time which is best to explain actual
observed choices (Boter et al, 2005),. Since RP approach uses data collected on real life
choices, the choices as made by individual decision makers are bound by the real

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
6
constraints confronted by those same decision makers. Researchers have contributed
value of travel time through RP survey method(Román et al., 2014),(Fezzi et al,
2014).Revealed preference survey is not adequate in case where a new transport
invention is under considerations, which necessitates the use of hypothetical scenarios.
In Stated Preference approach, information about decision maker’s preferences is
elicited by using specifically designed hypothetical situation. In SP approach, all
passengers were capable to make choices about preferred travel options and also able to
provide justifications for their choices(Jiang &Morikawa, 2004). Moreover, it is
possible to control the choices offered to respondents and thereby ensure data of
sufficient quality. This method permits generation of multiple observations per
respondents and are also asked to consider a number of situations in a set of option to
maximize their utility in this choice of transport system. SP method is considered as a
better method for value of travel time estimation because the travellers themselves
evaluate different trade off possibilities between travel time and travel cost. Research
has contributed to value of travel time through SP survey(Tseng &Verhoef,
2008),(Calfee& Winston, 1998). The underlying principle behind the preference is that
the results will reflect the revealed and stated behaviour of the preference of the people,
which is therefore nearer to the reality.
3.2 Challenges and mitigation for delay cost data collection
Measuring traffic volume count for roadway sections under varying traffic, traditional
data collection techniques such as manual and mechanical method or advanced data
collection techniques using sensors can be used.
Even though, several methods are available for travel time data collection, suitable
method need to be selected for travel time data collection under congested conditions.
For homogeneous and lane based traffic conditions, travel time data has to be collected
for the same type of vehicle, for that any of the methods such as a registration number
method, video graphic method and floating car method can be used. But in
heterogeneous and non-lane based traffic conditions, vehicle has to perform stop and go
conditions with available space of road stretches, and travel time differs for different
types of vehicle. Hence, travel time estimation by video graphic method gives more
accurate data than floating car method and registration number method in terms of
manpower and several runs for floating car.
In computing the value of travel time from the field, the challenges to be confronted as
that questionnaire has to be designed in such a way that it includes the trip
characteristics, trip maker’s characteristics, and vehicle related characteristics and
transport service characteristics. Hence, a suitable measurement to be taken for the
information regarding the characteristics of the field while experiencing congestion. To
address that, a pilot traffic survey needs to be conducted to identify the period of
congestion and those temporal variations to be included while making questionnaire.
Even though, underlying uncertainties makes estimation of travel time value more
vulnerable to the transport planners, the temporal variation identification holds good
estimates for economic estimation of traffic congestion delay impact.

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
7
4. Delay cost estimation for various Facilities
The road transport network system consists of different facilities and their performance
is different from one another. The economic cost may vary from one facility to another
facility and as a whole. The congestion mitigation measures including widening of the
road and provision of an overpass and under pass to be provide at dis aggregate level for
links and nodes in the road. Hence, it must be essential to study the congestion cost for
different facility. A method is proposed to estimate the delay cost for link, intersection
and corridor as separate facilities.
4.1 Delay Cost Estimation at link
Delay estimation at link is assessed based on the link travel time data during peak and
off peak periods. Even though, several methods are used to find out the link travel time,
registration number method gives the better result (Cambridge Systematics et al.,
2008).But in the congested condition due to several vehicles, video graphic method
provides more accurate data. Volume count for link can be done by either manual, video
graphic survey or any advanced data collection techniques. The link delay cost
estimation formula is shown in the equation 2.
iab
n
iablink votvtd ,
1


(2)
Where,  is the delay cost at link,  is the travel time delay between points a and b
in the link, v is the traffic volume on the link, ,is the value of travel time for the
link and i is the vehicle type.
4.1.1 Challenges and mitigation for delay cost at link
A number of connected link form a route. As the link is very short in length, the number
of passengers choosing to travel within it is a part of their trip.. Hence, the sample of the
travelers who uses the link is very difficult to identify. Hence there is an uncertainty in
the estimation of value of travel time for the link travelers. In order to mitigate this
stated preference survey has to be adopted in the locality including the link
characteristics such as link length, specified link travel time and frequency of travel
through link.
4.2 Delay Cost Estimation at Intersection
Delay is the effective measure used for the performance evaluation of the intersection
and is estimated as the extra time consumed by the vehicles in traversing the
intersection. The intersection delay cost formula as shown in the equation 3. Video
graphic survey, manual method and registration number methods are commonly
adopted data collection technique of traffic volume and delay at an intersection.
mimi
mi
n
i
k
m
tioner votvdelayd ,,
,
11
secint 

(3)

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
8
Where delay is the delay of the vehicle, v is the traffic volume, vot is the value of travel
time, iis the vehicle type and m is the different approaches for an intersection.
4.2.1 Challenges and mitigation for delay cost at Intersection
The value of travel time of travelers varies on each approach and the surveying is to be
conducted for each approach travelers separately .When vehicles move in a mixed
traffic regime, the travel time value of travelers using different vehicle types is also to
be estimated. Due to different approaches in an intersection, an estimation of value of
travel time is a complex task. Hence, Value of travel time for intersection associated
with stop and go the process of the vehicle can be assessed using the survey at network
level because the field survey is difficult to acquire as the people is an urge to pass the
intersection.
4.3 Delay cost estimation at corridor
Delay estimation at corridor is conformed through traditional travel time measurements.
Floating car method gives the best measure of the delay and volume along the corridor.
Several studies has been conducted to find the delay cost at corridor level(Harford,
2006),(Errampalli et al, 2015), (Well et al, 2011),(Goodwin, 2004),(T. Khan & Mcips,
2013). The equation to find out the delay cost at corridor is shown in equation 4.
i
n
icorridorcorridor votvtd  
1
(4)
Where,  is the corridor travel time delay, v is the average volume on the
corridor,votis the value of travel time and i is the vehicle type.
4.4 Discussion
To summarize, the primary impact of traffic congestion, delay and its economic
evaluation are examined in the present study. Systematic methodology proposed for
estimation of delay cost at link, intersection and corridor. Even though, several
techniques are available for data collection, challenges and mitigations in data collection
process and under congested conditions are explained.
5. Fuel Impact
The rapid growth of vehicles in the roadway tends to use the same road section at the
same time subsequently leads to wastage of fuel in the vehicle. The fuel consumption of
vehicles increases in the operation stages of vehicles. Fuel is wasted due to
acceleration, deceleration and idling of the vehicles and it leads to air pollution. This
operation arises in the congested conditions and subsequently leads to wastage of fuel
and indicated as an impact of traffic congestion. It is dignified based on the journey time
and fuel consumption rate during the journey time of the vehicle. Excessive use of fuel
in congested condition increases the road user cost.
Fuel economy of an automobile is the ratio of distance travelled and the amount of fuel
consumed by the vehicles. Stop and go process of vehicle during the congested period

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European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
10
TABLE 1. Fuel cost study performed in different countries
Author & year Country Formulae and Notations Remarks
Shabbar et al
2014(Shabbar,)
Pakistan   ∑∗  ∗ 

 FCC→ fuel consumption cost,
FC→fuel consumption quantity Fp→ fuel price
µ →proportion of vehicle FT→ fuel type, m→ vehicle type
Representation of mixed traffic
condition.
T Khan et al 2013 Bangladesh ∑∗∗∗
 C →cost of fuel per day,n→no of vehicle
A →average run per day FE→fuel efficiency,EC→fuel cost
Applicable in mixed traffic conditions.
Average run per day considered.
Sarkar 2012(Sarkar,
2012)
India    ∗ ∗ ∗ FLC→fuel consumption cost
IFL→dling fuel consumption (ml/m),D→delay (min)
FL→fuel rate (Rs/ml),n→No of vehicles
Best suited for idling condition.
Znatak et al 2011(Of
et al., 2011) Egypt   .  . 
AFC →average fuel economy in congestion
APS→average peak period congested system speed
Based on the speed of the vehicle
Darry j et al
2010(“The Economic
Cost of Traffic
Congestio)
Florida   
 ∗∗AFC →annual fuel cost,FC→ fuel economy
FE→ fuel economy DVHD→ daily vehicle hours of delay
APS→average peak period congested system speed , WD →working days
Based on the speed of vehicle and daily
delay of vehicle
Ubillos B
2008(Bilbao-Ubillos,
2008)
Canada    
C →financial cost due to additional fuel consumption,
P→ average price of fuel consumed
D1→ length of urban roadway,D2 →length of proposed alternative route
G1 →average in town fuel consumption of vehicle
G2 →average out of town fuel consumption of vehicle
Empirical equation
Theoretical derivation
LUO et al
2007(LUO, JUAN,
SUN, & JIA, 2007)
China    
C→ fuel consumption by congestion
Ctf→fuel consumption by transport
Vc→average speed at congested conditions Vo→ average speed at normal condition
Compare with normal conditions

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
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Fuel consumption from vehicle influences on the road characteristics, vehicular
characteristics and driver characteristics(Ma, Xie et al, 2015),(Boriboonsomsin & Barth,
2010).Therefore, assessment of fuel consumption impact on these factors is
indispensable for better fuel economy and congestion mitigation policies. Hence, fuel
consumption estimation is executed based on these factors by indirect method.
Several empirical models have been developed for the fuel consumption measurements
that linked to operating conditions and road geometric conditions. Initially, research
contributes to fuel consumption model by means of data correlating traffic operation
characteristics (speed) and road geometric characteristics (gradient, rise, fall and
pavement conditions)(A. S. Khan & Clark, 2010).
Pavement quality also affects the fuel consumption rate. The rise and fall of the vehicles
in the roadway increase the fuel consumption. Table 2 depicts the fuel consumption
measurements by various factors and its influence on the fuel consumption rate of the
vehicle.
Afterwards, researchers developed the mechanistic model, which predicts fuel
consumption based on the efficiency of the engine in converting fuel to energy and the
force acting on the vehicles. Mechanistic models are considered as superior to empirical
models because it directly accounts for the individual vehicle characteristics and the
forces acting on the vehicle. But due to prolonged break, this will make an
exception.Mechanistic model mainly considers the vehicle characteristics does not
capture the performance evaluation of transportation system properly.
5.1.1Challenges and mitigation for estimation of data for fuel consumption
Fuel cost is estimated based on the types and number of vehicle experiencing
congestion. Fuel consumed in each vehicle varies depends upon the condition of vehicle
and types of fuel also have a variation such as petrol, diesel and compressed natural gas.
These parameters make an uncertainty in the valuation of fuel cost. Therefore, types of
vehicle and its fuel type has to be collected separately from the field while experiencing
congestion with the aid of manual method and video graphic method.
Fuel consumption depends on the aggressiveness of the driver. Aggressiveness of the
driver may vary from normal conditions to congested conditions; a separate study has to
be conducted to incorporate these conditions.
The fuel cost is highly sensitive to the cost of the fuel. As the fuel cost rise, fuel
consumption cost is also high. Hence, the fuel consumption cost may vary from time to
time depending upon the cost of fuel. Even though, the cost of fuel is fixed one for a
specific time period, types of vehicle and fuel used in the vehicle which embedded in
the congested condition has to be measured to predict the impact of congestion
accurately.

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
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TABLE 2. Fuel consumption empirical models
Author & year Formulas and Notations Remarks
Sierra
2016(Sierra,
2016)
   ∗ ∗

FC →Total fuel consumption of road fleet
VP→total vehicle population
VKT→average vehicle kilometer travelled
FE→ average fuel economy,i→vehicle type,J→fuel type
Based on fuel
economy. Vehicle
type and fuel type
are considered
Rakha et al
2011(Rakha,
Ahn)
 


FA → fuel consumption or emission rates for every speed
Acc→ acceleration
S →speed of the vehicle
Empirical model
considering the
speed of vehicles
H Wang et al
2008(Wang,
Fu, Zhou, & Li,
2008)
   ∗


FC→ Trip fuel consumption, I→ no of bins
i→ speed-VSP bin index, Ti → vehicle trip time speed
FR→ fuel consumption rate for speed-VSP bin
Mechanistic model
based on vehicle
specific power
Hall
1992(Hall,
1992)
  . . ..
F→ is fuel consumption at cruising speed (gallons/mile)
V→ is average speed (miles/hour).
Cursing speed
considered
Chensher and
Harrison
1987(Chesher
& Harrison,
1987)
     
FC→is the fuel consumption
S→ vehicle speed in km/h
IRI→ international roughness index
RISE→ rise of the road
FAL L → fall of the road in m/km,a0 to a5 are constants
Empirical model
considering vehicle
speed and pavement
characteristics
5.2 Discussion
The fuel impact and its economic evaluation are reviewed. Fuel consumption is
measured by direct and indirect method under prevailing conditions. Direct method
gives the fuel consumption rate of a vehicle directly for normal and congested
conditions. Moreover, while taking the measurements, the representation of the
aggressiveness of the driver and types of vehicles are to be incorporated. In the indirect
method, several empirical relations can be represented as an indicator of congestion
such as average speed of vehicles.
6. Emission Impact
Emission impacts are offseted by the increase of vehicle in the road and also vehciles
tend to use the same road at same time regularly,which leads to severe air
pollution.Vehicular emissions from the traffic are the primary source of air pollution in
the urban area. It consist of pollutants such as carbon monoxide, carbon dioxide, nitrous
oxides and particulate matter (Zhang et al, 2011) and cause health problem to the road
users. Prolonged carbon dioxide emission from the vehicle contributes to global
warming and also significantly affects the ambient air quality.The magnitude and

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
13
intensity of emission depend upon the tarffic activity, traffic performances in the
roadway,fuel consumption rate and emission control srtategy of vehicles.
Traffic Congestion has been indicated as the main contributor to air pollution by
vehicular emission. The negative effect of pollution depends not only on the quantity of
pollution produced, but also on the types of pollutants emitted as well as the conditions
into which they are released. The vehicle emits pollutants such as carbon monoxide,
carbon dioxide, nitrogen oxide and other particulate matters to the environments. Due to
the stop and go conditions during congested periods, vehicle emits more pollutant than
normal steady state conditions.
The emission impact of congestion was calculated based on the fuel consumed and
number of pollutants burned. Emission cost of an automobile is related to the distance
travelled by the vehicle, number of vehicle and emission factors of pollutant that emits
from the vehicle. Table 3 represents the work done in different countries to assess the
emission cost. Emission cost of a particular component derived from traffic is calculated
from the following equations 6.
ff
n
iit celve  
1
cos (6)
Where e cost is the emission cost of pollutant, v traffic volume, l is the length of the road
section,is the emission factors per unit weight of pollutant, is the value of the cost
of pollutant and i is the vehicle type.
Data requirements and data collection methodology for emission cost
The emission cost components comprise traffic volume, length of the road section, cost
of pollutant and emission factors. Traffic volume under various traffic flow are
measured any of the methods that explained above. Information about the cost of
pollutant is given by the locality under the survey.
The idea to measure emission factors can be done by two methods namely direct
method and indirect method. In direct method, pollutants emitted from the vehicle are
assessed based on the portable emission instruments which are fitted to the vehicles.On
board emission measurement can be done using instruments. The instrument carrying
vehicle run along the stretch of the road gives emitted particle directly.
PEMS (Portable Emission Measuring System) represents an advanced emission data
collection technology. GPS is enabled in vehicles and this system is made to run along
the study stretches which will bring out the emission data. PEMS provide emission data
from the field and used in many studies,(Wyatt et al, 2014),(Liu et al, 2010),(Tong et al,
2000).
The different factors that influences the vehicular emission are vehicular characteristics,
fuel characteristics, emission control strategy and operating condition of vehicle (Franco
et al., 2013). In indirect method, emission factors are derived using the factors which
affect congestion such as vehicle parameters, driving conditions and fuel consumption
rate.

European Transport \ Trasporti Europei (2018) Issue 68, Paper n° 5, ISSN 1825-3997
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TABLE 3. Emission cost study performed in different countries
Author
& year
Country Formulae and Notations Remarks
Alexan
der et al
2013
USA     , 

,→Unit cost of emission pollutant
→Emission rate of pollutant(Kg per vehicle mile)
P→ pollutant
Cost is based on
the vehicle mile
travel on the
vehicle and its
pollutant.
Sarkar
2012(S
arkar,
2012)
India    ∗  ∗ 
Pc →Pollution cost
Conc →concentration of pollutant
(total vehicle population * emission factor)
D →delay of vehicle
cost →* cost per kg of pollutant
Best for both
homogeneous
and
heterogeneous
traffic
conditions.
Znatak
et al
2011
Egypt  

→cost of carbon dioxide
→Weight of carbon dioxide
 →Unit cost of carbon dioxide
Only carbon
dioxide cost is
considered
The speed of a vehicle is the governing factors that control emissions of a pollutant
from vehicles. Several researches have been done to find instantaneous emission by
considering speed variation (Ahn et al, 2002), (M. Wang et al, 2011).Dynamometer test
is one of the traditional methods to find out the fuel consumption and emission factors
under laboratory conditions. It tests the operational condition of vehicles, namely speed
of the vehicle. It consists of driving cycle that contains stops, starts, and idling of
vehicles which provide the overall weighted average of speed. The limitation of this test
is that it does not account for actual driver and field conditions. The study has been
done to find the emission factors using dynamometer test,(Samuel et al., 2006).
An empirical model for emission was developed by Cappiello et al(2002) considerding
vehicle characteristics.They developed a model for engine out emission and tapline
emision model.The emission level during idling, acceleration and deceleration
conditions of the vehicle in the congested traffic were studied widely. Idling reduction
option for heavy duty vehicles trucks and diesel vehicle were studied by Gaines et
al(2009)(Gaines, Hartman, & Solomon, 2009).
Challenges and mitigation for emission cost data collection
The emission rate of pollutant from the vehicle is an important parameter in the
estimation of emission cost. In direct method, portable emission monitor is fixed in the
vehicles to get the emission rate of pollutant during normal and congested
conditions.Driver behavioral characteristics have a direct impact on the emission of
pollutant. Hence, during the operation of vehicle in the direct data collection technique
various driver behaviors have to be incorporated.
Even though, several methods are used in the indirect method for emission rate
calculation, congestion indicators such as speed and fuel consumption rate are to be

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15
accurately measured in the locality to provide an accurate database for emission
estimation.
Excessive emission occurs when the vehicle undergoes in the congested conditions. The
emission rate of pollutant from vehicle depends upon the vehicular characteristics such
as type of vehicle and emission control strategy of the vehicle .Depending upon the type
and condition of the vehicle the emission varies from vehicle and thus makes remarks in
the cost calculations. Hence, it is essential to provide advance emission control
strategies to every vehicle.
Discussion
The emission impact and its economic evaluation are reviewed. The emission factor of
each pollutant which is emitted from the vehicle is estimated by direct and indirect
method. In direct method, on board emission instrument which can fit on different
vehicle provides the pollutant and its emission rate directly from the field for both
normal and congested conditions. In indirect method, the factors which are influence on
the vehicular emission which is also a parameter of traffic congestion has taken into
account.
Challenges ahead and Research direction
The objective of studying the economic impact of traffic congestion is to propose a
realistic estimate of the economic value of traffic congestion, which is being used for
the evaluation of many highway improvement proposals such as congestion mitigation,
cost benefit analysis and carbon credit for the project. Detailed study and gap to be
addressed are summarized below.
Delay impact causes to travelers to wait in the queue for a period of time and thus by
losing their important time. Therefore, delay is an unwanted travel time for the road
users. Delay cost is estimated by the difference between the average travel time of both
normal and free flow conditions, traffic flow in the roadway and value of travel time for
travelers.
To combine engineering and economic perspective of delay, the value of travel time for
travelers plays a major role. A review has carried out to estimate value of travel time. As
traffic congestion has both spatial and temporal variation, delay cost estimation differs
with respect to these factors. The review stated that preference survey provides most
scientific method of estimating value of travel time at congested conditions. Different
stated conditions are to be added in the surveying process of the value of travel time for
different facilities because of the variation of the travelers’ trip length, travel time for
their trip and frequency of their trip along that route.
Even though, each facility contributes data to the estimation of value of travel time.Data
requirement and data collection of delay cost varies from facility to facility. This review
proposes different data collection techniques, and its advantages and dis advantages and
best data collection process.
More vehicles tend to use the road at the same time, fuel consumption rate of vehicle
increases and thus by increasing the operating cost of vehicles. Fuel cost in the

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congested condition is estimated by the extra fuel consumed during congested period,
number of vehicle and cost of fuel. The traffic regime consists of different vehicles and
having different vehicle characteristics. Hence, the complexity arises to calculate the
fuel cost of each vehicle in the road way. Therefore, the vehicle characteristics such as
type and make of vehicle are to be noted down while taking the data collection for the
fuel cost. The cost of fuel may vary for a period of time. Hence, cost of fuel variation
taken into account while forecasting fuel consumption cost.
Indirect method describes a different fuel consumption model based on the empirical
data set. This estimation considered the factors affecting fuel consumption such as
vehicle parameters, driving condition and pavement conditions. A challenges in the
quantification of the fuel consumption using empirical method is that whether it
represents the congestion adequately. A drawback for considering the average speed to
predict congestion is that, the same average speed result in both peaks and off peak
periods.
The different Pollutant emits form the vehicle causes air pollution in the area. Traffic
congestion causes the vehicle emission. The emission cost is estimated by the emission
factor of pollutant per unit weight, length of road section travelled and cost of pollutant.
Direct and indirect method gives the emission rate of pollutant from vehicle. While
taking the measurements from the direct method, the aggressiveness of the driver has to
be tackled since the roadway accommodates different drivers behaving in a different
manner.
In indirect method, by use of the indicators of congestion such as average speed, idling
of vehicles can take to find the emission factors of each pollutant. This may cause bias
estimates because it represents a vehicle emission and a driver behavior. In order to
overcome that research has also to be focused on the driver behavioral and vehicular
characteristics of emission while measuring through direct method to get accurate data
for congestion.
Conclusion
This study presents a review of the different traffic congestion component, their
economic evaluation, and the challenges associated with quantifying each component.
This review highlights the various methods proposed by different researchers.
Therefore, in order to assess the overall economic impact of traffic congestion, it is
essential to take into account of all the relevant components and their economic value.
Even though, there is a considerable uncertainty in quantifying the impact of congestion
in economic terms, this paper provides an insight to do that.
Acknowledgement
The authors sincerely thank the support received from the Centre for Transportation
Research, Department of Civil Engineering, National Institute of Technology Calicut, a
Centre of Excellence setup under FAST Scheme of MHRD, Govt. of India.

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