Feedback Approach for the Dynamic Interactions Between Urban
Transportation and Air pollution
Nam Hee, Choi Sun Kyoung, Kim Min Ki Hong
Dept. of Public Administration, Chongju Dept. of Urban Administration, Dept of Public Administration, Chongju
National College, University of Seoul National College,
367-701, Youngang-1i 3, Jeungpyoung- 135-010, Sungwoo Village 301, 367-701, Youngang-ri 3, Jeungpyoung-
eup, Chungbuk, Korea, 21-3 Nonhyun-dong, Kangnam-ku, — eup, Chungbuk, Korea,
Tel: 081-43-820-5294 Seoul, Korea, Tel: 081-43-820-5291
Fax: 081-43-820-5231 Tel: 081-2-3442-6086 Fax: 081-43-820-5231
E-mail: dmchoi@ cjcnet.chongjunc.ac.kr ~—_ E-mail: skkkim@netsgo.com E-mail:mkhong@ cjcnet.chongjunc.ac.kr
Abstract
To solve the policy problem between transportation and environment in trade-offs, above all, it is necessary to
understand the complicated relationship between transportation and environment clearly before selecting policy
alternatives. From this point of view, this study will propose the logic structure to examine the complex interaction of
transportation and environment and investigate theoretically what kinds of impact would appear by the air related
polices.
In this research, we used 'system-dynamics' which investigates the complexity through the flow of information
and materials and the interaction of elements, which constitutes systems. System Dynamics is an approach that the
variables to decide structural relationship in a system affect one another not in only-way but in inter-way and the
power of influence changes time by time.
This research is trying to examine the complex interaction of transportation and air pollution. For achieving this
purpose, causal maps in System Dynamics approach were used. The main issues are as follows; first, to investigate
the dynamic relationship between transportation and air pollution caused by exhaust emission gas. Second, to
structuralize the logic of simulation to experiment the impacts of policies to relieve air pollution.
Keyword: urban transportation, air pollution, feedback structure, fuel & vehicle
I. Introduction
Nowadays, local governments are trying to achieve two aims properly; one is that they should
activate economic conditions such as transportation and the other is that they should improve the quality
of environment to enhance citizen's life quality. But these are in trade-offs. So that it's not easy to meet
with the policies achieving two aims at the same time. The difficulties in responding this problem can be
explained with the inseparable relation of transportation and air environment. For example, the
investment to transport services may bring about a bad condition in the air by letting out more fumes
because of more traffic. And the opposite situation may lead to shrink of economic activity.
Local govemments have focused on making better their economic conditions by investing in
transportation system such as roads before the recognition of the atmospheric pollution is raised in cities.
This phenomenon can be seen in Seoul, which has invested 30% of its budget to the expansion and
improvement of road facilities every year. Seoul local government invested 5~7 trillion won, 30~40% of
the total budget including general and special accounts every year, in transportation facility from the year
1997.
But as o-zone warnings were appeared 40 cases in the year 2000, which were only 5 cases in 1995,
and are threatening people's life directly and more frequently, local governments and citizens recognized
the quality of atmospheric environment is not a less important factor to decide the quality of life than
economic conditions (convenience) just like harmonious traffics. A series of these changes proposed
policy problem to peruse the improvement of air environment and the expansion of city services
(facilities) simultaneously.
Thus, to solve the policy problem between transportation and environment in trade-offs, it is
necessary to understand the complicated relationship between transportation and environment clearly
before choosing policy alternatives. From this point of view, this study will propose the logic structure to
examine the complex interaction of transportation and environment, and will investigate theoretically
what kind of impacts the air related policies would have on the two through policy causal maps.
In this research, we used 'system-dynamics' which investigates the complexity through the flow of
information and materials and the interaction of factors, which constitutes systems. System Dynamics is
the approach that the variables to decide structural relationship in a system affect one another not in only-
way but in inter-way and the power of influence changes time by time.
This research is trying to examine the complex interaction of transportation and air pollution. For this,
causal loop diagrams in System Dynamics approach were used. The main issues are as follows; first, to
investigate the dynamic relationship between transportation and air pollution caused by exhaust gas.
Second, to structuralize the logic of simulation to experiment the impacts of policies to relieve air
pollution.
II. System thinking about relationship between urban transportation and
air pollution
1. Traditional approaches for transport and air pollution and their limits
There have been many researches to understand, analyze and solve the transportation and air pollution
problems. Former studies (Lee, S. W., 1996; Lee, S. H., 1998) assumed one-way cause-effect relationship
that as people's activity increases in the city traffic volume substantially increases then air condition
deteriorates and finally the quality of life is lowered.
Meanwhile, the main method of the above studies (Han, S. G., 1996; Gang, H. B., 1998 etc) is to
divide traffic condition and air pollution condition from the past to the present of one particular area, to
investigate them separately and to analyze them only numerically. This results in the fact that traffic
volume and air pollution increase continually and transportation is the main source of air pollution. So it's
enough to try solving the problem only around the transportation side. So the researches proposed
technical methods to lower air pollution mainly focused on problem-solution around transportation. But,
we think that these studies made three mistakes.
First, they supposed transportation-air pollution relationship as one-way. But this idea is so stagnant
because in reality transportation and air pollution affect each other in feedback.
Second, the means of analysis is so parametric. That is, they pulled out problems by comparing two
factors numerically. But, because sub-systems are changing, and there are lots of social phenomenon not
expressed in number and many kinds of situation appeared in non-linear relation, it's very hard to
understand various situations with this method comprehensively.
Third, there is simplicity in policies suggested in their studies. They focused on transportation
because transportation-air pollution relationship was assumed one-way, therefore suitable resolutions
were not proposed according to the dynamic situations.
2. Theoretical study of transportation-air pollution relationship through system thinking
1) System thinking approach for the transportation-air pollution relationship in urban system
System thinking is considered as a frame of new thinking, which overcomes existing one-way
thinking. Basic features of the complex human system are that there are so many cases in which causes
and effects are not directly combined in space-time, multi-factors get mingled one another and
fundamental differences between the changes for short-term and long-term exist. So the thinking may
incur serious errors to understand problems exactly and prescribe the policy properly; stagnant think that
independent variables affect dependents only in one-way, partial thinking that handles systems in part not
in whole.
So as to overcome the limits of the linear and unidirectional thinking, system thinking emphasizes
that primary factors are connected with one another in circular causal relations, their relative importance
can be changed so we should pay attention to overall change patterns for a long time and it's necessary to
harmonize analytical thinking with integrated one.
Urban transportation is not the self-end, but a means of satisfying demand derived by economic
development. Today urban demand for transportation is increasing abruptly and this affects environment
directly or indirectly. So traffic problems have been discussed linked with economic and environmental
aspects. The linkage among economic development, transportation and environment can be looked at the
following Figure 1.
motorisation
suburbanisation-
Ll income gown
[ease JES] Bee]
j<—— | weak
a we con ») =a
environmental loac
strict Ly
sbobanaat —
To ficient ty
|——alhaith compact [>faene tof
a tip length | >] in energy consumption
land use devetspmend’ Utielengih] [in energy coneumptios
Figure 1. Interactions among urban transportation, and economic development and environment
First, economic development increases production and traffic volume. This leads to worse
environmental condition due to inefficient energy consumption by traffic congestion.
Second, economic development increases urban income and this can be divided in two ways. One is
that increased urban income produces more vehicles. The other is that it makes people to use cars than
public ones and to expand traveling distance because of sub-urbanization. Consequently, traffic jam,
ineffective energy consumption and deterioration of air are getting worse.
Third, economic development promotes urbanization. Population and industry are concentrated and
traffic congestion occurs due to more traffic volume. In the end, the quality of environment gets worse.
The relationships among economic development, transportation and environment are shown in
<Figure 1>. Next we will explain the relationships between economic development & transportation and
transportation & environment, especially about the air pollution.
Economic development and transportation
Demand for transportations is derived by urbanization and urban sprawling, ie. urban growth and
development. Nowadays individual countries, especially developing countries are experiencing the
importance of transportation in metropolitans and therefore the problems are produced by more
dependency on land transportation due to urbanization. To resolve this problem, they have carried out the
policies to invest in transportation part mainly but couldn't afford to catch up with urban sprawling
because of growing population. Simultaneously sub-urbanization, especially sprawling sub-urbanization
accelerates motorization because unprepared public transport makes suburbanites depend on their own
cars. The negative feedback of sub-urbanization and motorization involves in negative synergy and incurs
the gradual increase of traffic energy consumption. Today inter-urban transportation problems occupy the
majority of transportation issues, so they are as seriously considered as internal-urban transport problems.
Transportation and air pollution in dynamic urban system
Transportation is the main eneryy-consumer and air-pollutant in cities from the producing phase of
vehicles, parking lots, roads and so on, to the operating phase of vehicles and to disposal phase of waste
tires and used cars.
Developing and developed countries have been experiencing serious air pollution by exhaust gas of
growing number of land transport as well as population concentration due to industrialization and
urbanization. That is to say, urbanization and motorization have brought about deterioration of the air in
cities. In a practical circumstance that the volume of vehicle's sale is increasing rapidly especially in
developing countries among OECD countries, one gallon of oil consumed by vehicles discharges 19
pounds of C02 to the air directly and NOX discharged by human activity occupies most of transportation
section. NOX is discharged as a combustible of fossil fuels during internal combustion in addition to
vehicle 1/3 - 1/2 of NOX discharge originates in transportation domestically(Gray Hag 1997).
There are various pollutants emitted by cars, among them CO, NOx, HC and PM are principal
pollutants, 82% of the air in Seoul. The main troublemaker related to exhaust is light oil-used vehicles,
which emit enormous pollutants. Large-sized buses and trucks, for instance, are observed to emit 5 to 20
or 30 times more pollutants than cars, according to emission quotient. By the way, the decrease of vehicle
speed because of traffic jam causes unnecessary energy consumption. For example, the gasoline oil-used
vehicles with 20km/h is efficient with 1 Yaimes more than ones with 10km/h and 40 to 70km/h is the
most energy-efficient.
City is a huge system. Cities have a cycle of growth, transition and decay changing dynamically and
urban growth is formed by interaction of economic, socio-cultural and environmental factors through
feedbacks. Transportation and air pollution as a sub-system of the dynamic urban system, also involves
complicated dynamics. Interacted circular causal relationship between these systems can be explained
like this;
To begin with, the growing number of urban population increases traffic volume. The traffic volume
makes traffic congestion, average traffic speed lowered and it brings out more serious air pollution. The
air deterioration stimulates the crisis for environment. So the necessity to regulate transportation part is
proposed and such policies are adopted as environmental tax-levy, affordable exhaust standard,
preferential treatment for small car, efficient energy use, etc. These policies decrease traffic volume and
as a result, air condition gets better. But on the contrary, when regulations get weakened, traffic volume
will be larger and the air will be worse because of more exhaust produced by vehicles. The circular causal
relationship will proceed repeatedly. Now the complex relationship between transportation and air
pollution should be investigated to solve dynamic inter-way feedback problems.
2) Basic feedback structure of interactive relationship between transportation and air pollution
As mentioned above, transportation and air pollution are in circulating cause-effect relationship of
feedback loop. The basic structure of this is shown in <Figure 2>. There are four feedback loops.
Environmental
regul ation( level)
Transportation Capacity
Traffic demand
Quality of
Transportation urban
Investmen
— envionment
an(ol
Traffic volume
Congestion(- travel
see a se
4 Amount of
Emission
Si (4) y
Figure 2. Basic Feedback structure between urban transportation and environment
First one is the negative feedback loop. Negative feedback loop is called self-restraining feedback or
stabilizing feedback and is indicated as a sign of minus, - sign at the center of a circle. For example,
negative feedback loop shows what mechanism is implied filling a cup with water to the desired line.
Once the desired line is decided, it begins to fill a cup in case it's empty. When the water is enough to
approach the line, it begins to slow and stops, finally achieving stabilization (Kim, D H. etc., 1999). In
the case the traffic volume and congestion, when traffic volume increases congestion increases as well,
but when traffic congestion increases traffic volume decreases because demand for transportation
decreases due to increasing gas consumption and cost by traveling time.
Second one is the positive feedback loop. Positive feedback loop is often called self-reinforcing
feedback and is indicated as the sign of plus, + sine at the center of a circle. An armament race between
countries is the example showing the positive circulating relationship. It's why the armament race is
increasing between country A and B; The arms of A threatens B and B expands her armaments in return
but this threatens A and A expands armaments as the results. The behavior between two countries repeats
the vicious circle (Kim, D H. etc., 1999).
As same as this feedback loop, when traffic volume increases, traffic congestion increases and for this,
investment in transport increases i.e. traffic capacity increases. But this finally incurs growing traffic
volume. The phenomenon circulates repeatedly. This is why traffic congestion is continually increasing
although Seoul has invested trillions of won in roads.
Above these two loops, we can suggest that because traffic congestion by increasing traffic volume
will be stabilized naturally as time goes on, imprudent supply-oriented traffic policies. Investment on
SOCs has been focused on road construction and the policies of supply-oriented transportation have been
implemented in Korea. But once roads are constructed, cars dominate most of them. So in fact the
concentrated investment in roads operates as the same action of supplying the subsidy to cars. This
distorts the desirable investment in SOCs in the end (Min, M. G., 2000) may only increase traffic volume
and offset the effects of environmental policies.
Third one shows negative feedback loop of traffic speed and environmental regulation. The increasing
demands for transportation exhaust more not only because traffic volume gets larger but also because the
traffic congestion due to shortage of road capacity lowers the traffic speed. Accordingly, regulating
policies get reinforced to reduce traffic volume and this relieves traffic congestion, finally traffic speed
increase.
Fourth one is the negative feedback loop of traffic volume and environmental regulation. When traffic
volume increases, exhaust gas is produced more lowering the quality of environment. This heightens the
crisis for environment and the necessity of environmental regulation suppresses the demand for
transportation. It lowers the exhaust gas and thanks to this, urban environment gets better. But if so, when
regulations get softer, the traffic volume will be larger again.
The fundamental feedback structure of transportation and environment can be summarized simply
like this: If air pollution produced by growing traffic volume gets worse, then environmental regulations
are carried out and this reduces the traffic volume.
Besides simple feedback structure, it is necessary to understand fully the complex relationship
between transportation and air pollution to structuralize the logic of policy simulations. So next, we'll
structuralize all factors' feedback loops and observe policy leverage.
III. Analysis of causal maps of dynamic relationship between transportation
and air pollution to search for policy alternatives
As a methodology of system dynamics, causal loop diagramming is a basic work to search for
appropriate policy alternatives by helping to understand the complex relationships between systems.
As mentioned above, transportation and air pollution are in the interactive feedback relationship. But
we can't suggest policy, which solve the problem of interrelated system simultaneously with only one
feedback loop. So we will first look at feedback structure of transportation problems through a causal
loops and then, we'll look at interactive causal loops of system factors.
Urban policy should be approached with the long, integrated sight and in this point, causal loops can
give a great help to policy-makers because they are aggregated level of models which show the circular
causal relationship of urban growth and feedback structure (Kim, D. H. etc., 1999)
1. Traffic demand and air pollution
The level of air pollution in the city is basically a function of traffic demand and traffic volume.
<Table 1> shows that Seoul had 2,300,000 cars in 1999 which had only 1,375,000 in 1991 according to
economic development and the increase of household income.
We can check traffic volume also increased depending of the increase of vehicles in <Table 2>.
Increasing rate of in-outflow of Seoul in 1990 to 1997 is three times more than the one of gross passing
volume. This means traveling distance and time get longer as home and work get divided due to new
towns. Accordingly, the exhaust gas of car increases.
Table 1. Trend of total registered motor vehicles
1981 1986 1991 1996 1999 _| Increase rate
Capital region) 291,121} 700,501} 218024] 448145) 931,90) 19.0
Seoul 221,644] 521,521] 1,374,67| _2,168,18) _2,227,90 155
Kyoung Ki 49,082 | 140,573| 610,168] 1,809,62)_2,133,38 26.2
Inchon 20,395 49,407 | 195,395] 503,645] 570,610 22.9
National™ 571,794] 1,309,43) 4,247,81| 9,553,09] _10,732,7 19.9
Ratio(%
atio(’s) 50.9 54.3 513 46.9 46.0
(a)/(b)
Table 2. Trend of total traffic demand of Seoul
(Unit: 1,000 trip)
1990 1997 Increase rate
Total traffic demand 2,404 2,720 10.4%
Tn-out Flow traffic demand 475, 613 29.1%
In-out Flow traffic demand ratio 19.3 22.5
So pollution by cars in the air had increased 83.8% in 1998 from 60.8% in 1992, and it's necessary to
understand basic interaction of the increase of traffic volume, traffic demand, and air pollution in order to
decrease the growing rate of air pollution by transportation.
Table 3. Trend of total air pollutants and It’s ratio by vehicles
(Unit: 1,000 ton)
2 %B 4 % 6 7 8
Air pollutants | 4868 | 4584/4526 | 4350 | 4425] 4305 | 3,768
National |"Air pollutants | 1,839] 1,664] 1,645/ L710[ 1,702] 1,795] 1,552
By vehicles (%) | (37.8) | (36.3) ) (36.3) | (39.3) | (38.5) | (41.1) | (41.2)
Air pollutants 70; 534] 455; 422] 306| 308] 334
Seoul | Air pollutants 462 383 351 341 326 331 280
By vehicles (%) | (60.8) | (71.6) ) (77.1) | (80.6) | (82.3) | (85.3) | (83.8)
The causal loops are shown below (Figure 3). It is the control of traffic demand that functions as a
policy leverage, playing an important role of linkage of transportation and air pollution.
‘Transportation
demand
i me Management \
) Traffic demand
Number of car
Needs for
vehicles _ + regulations
+
%
# Traffic volume {—
+ \e Air pollution
+
Amount of emission
(air pollutants)
Figure 3. Feedback structure between urban transportation demand and environment
2. Transportation mode and air pollution
One of the most important things in the interaction of transportation and air pollution is the
relationship among the type of vehicle, the volume of exhaust gas and the type of pollutants. When we
look at the pollutants discharged by cars, mostly CO and NOX contribute to the air pollution.
Passenger car
Perr PM Sox
Bus Truck
Figure 4. Air pollutants emission rate by vehicles
The relative importance of exhaust gas is different by a type of vehicle such as cars discharge more of CO,
NOX and HC, NOX and CO in case of bus and CO and NOX in truck. It is shown in Figure 4 that point out
CO and HC are discharged mainly by cars and NOX and PM are discharged mainly by large trucks.
Table 4. Vehicle type Dependency of emission factors
(Unit: ton/year)
Number of [Travel distance] co HC Nox | pM S0;
Vehicles (km) ;
Passenger | Gasoline | 1,634,588 36 56,546 | 8,996 | 8,996 | 214 34
Car LPG 74,682 177 28,819 | 3,464 | 3,897 0 0
Gasoline 27,410 33 2,063 | 166 | 475 3 0
Small
a Diesel 170,636 53 4,597 397 | 4,795 | 1,158 | 586
S Medium 3,184 44 100 42 81 33 14
Large 15,802 105 7,241 | 1,058 | 7,755 | 1,221 | 354
T Small 244,240 56 8,839 | 794 | 7,399 | 1,837 | 861
r
u Medium 32,097 57 1,322 557 | 1,067 | 436 285
: Large 45,928 70 16,651 | 2,188 }15,422| 2,422 | 904
Total 2,248,567 630 126,178 | 17,663 | 49,888 | 7,325 | 3,039
Therefore it is needed to focus on the relationship between transportation and air pollution by the type
of vehicle and to search for policy leverage to reflect the feedback. When we indicate the dynamics
between a type of vehicle & air pollution and the policy leverage (control of traffic demand by a type of
vehicle and pollutants), it is as follows (Figure 5). The Figure shows the policy proving is important
between a type of vehicle and air pollution.
Emission standards
Ke oS
Traffic demand ae _Erronmental
by vehicle type "apy At regulation evel
vehicle type :
fstner oe — , 4 Air pollution
Geliles by ‘Traffic volue(by level by
Rie type of vehicles) pollutants type
*
Ss ee J
Z Fuel &vehicle
type dependancy of
emission factors:
Figure 5. Feedback structure between transportation mode and environment
11
3. Travel speed and air pollution
The main factor of discharge increase in Korea is the increase of fuel consumption by the decrease of
average traffic speed caused by traffic congestion. Specially, CO is emitted heavily by traffic congestion
and the pollution degree is showed very high at an edge of downtown road where traffic jams are severe
(Han, W. G., p12). While the traffic speed of car was 22.9 /h(2.49 _/h decrease in contraction to 1999
year) in 2000 in Seoul, urban bus was 18.99 /h(0.22 /h decrease in contraction to 1999 year). In
addition, (Table 5) showed the relationship between traffic speed of car and exhaust gas volume.
Pollutant exhaust coefficient is varied according to average traffic speed regardless of a type of vehicle.
Table 5. Trend of Average travel speed of Seoul
(Unit: km/h)
Year ‘93 | ‘94 | ‘95 | ‘96 ‘97 | ‘98 | ‘99 | ‘00 | ‘99/00
Passenger car 23.53 | 23.18 | 21.96 | 20.90 | 21.06 | 25.41 | 25.41 | 22.92 | -9.8%
City Bus 17.02 | 18.42 | 18.79 | 18.35 | 18.69 | 20.07 | 19.21 | 18.99 -1.1%
Table 6. Speed Dependency of Emission Factors for Gasoline Passenger Cars
Pollutant type cc Speed range Emission Factor
10-60 260.788*V “{-0.910)
co all
60-130 14,653-0.220*V +0.001163*V “2
NOX 1.4<cc<2.0 10-130 1.484+0.013*v+0.000074*v72
Gasoline passenger 10-60 19.079*V ~0.693
Voc all
60-130 2.608-0.037*V +0.000179*V “2
10-60 606.1*V “{-0.667)
Fuel Consume | 1.4<cc<2.0
60-130 102.5-1,364*V +0.0086*V “2
So traffic speed is an important factor to probe the relationship between transportation and air
pollution too and a causal loop between transportation and air pollution should be searched for at the
level of policy leverage around these factors. The causal map is as following.
At the next Figure 6, the traffic volume decreases by a control of traffic demand is connected to
exhaust gas volume decrease but an investment in the environment capacity of road releases traffic
congestion and increases traffic speed. Consequently, this results in the increase of traffic volume and
finally ends in growing amount of exhaust gas.
12
a
Number of gt
Tr, fic dem
+
a— Needs for
vehicles
TDM + environmental
4 regul ation
+ +
a vol ume
Cod AO Air pollution
Travel Tsice e gyre!
“Pe of
emission
Investment for
environmental
capacity of road
Figure 6. Feedback structure between travel speed and environment
4. Fuel of vehicle and air pollution
In case of Seoul, the portion of light oil used vehicle in pollutant exhaust volume is 43.6% of total and
it also produces 98% of PM and 74% of NOX. Accordingly, the contamination level by light oil used
vehicle is very serious. Generally, the pollutant from a vehicle is varied with its engines and fuels. For
example, a vehicle using gasoline and LPG emits mainly CO and HC, a bus and truck using light oil
discharge NOX and smoke pollution abundantly (the ministry of environment, 1999).
Table 7. Emission rate of gasoline and diesel
Emission rate
Total Passenger car Diesel
(Gasoline) Total Bus and Truck
National 1,552 641(43.1%) 911(58.7%) 665(42.8%)
Seoul 280 158(56.4%) 122(43.6%) 83(29.6%)
Hence, it is important to grasp interacting loop on the interrelationship between fuels and pollutants
and to establish the logic of policy simulation according to this.
13
Traffic volume
of diesel
vehicle
(afte demand
Wiberar of diesel
Diesel Vehicle vehicle
Enforcement of Air pollution
Te 7 Clean Fuel Level
iaclupci (Gp eesti "
emission oy + +
standards a=
Emission by
~— wa Needs for
Gasoline price Regulation by t _ Regulation Pollutants
sorts of fuels ¥
Mather of + : Trafic volume of
Gasoline Traffic demand of Geschvelacle
Vehicle Gasoline vehicle
+
+
Figure 7. Feedback structure between Fuel and environment
IV. Policy simulation structure based on the dynamics of urban
transportation & air pollution interactions
In the above causal maps, we examined 4 causal loops to be considered seriously in the transportation
-air pollution interaction (Figure 3, 5, 6, 7). At this part, based on the above, the causal map of
transportation - air pollution will be reconstructed (Figure 8). In Figure 8, 4 air pollution reduction
policies are presented(environmental tax-levy, affordable exhaust standard, preferential treatment for
small car, efficient energy use policy)) These policies were selected from Seoul metropolitan air
environmental improvement planning in 2000 _, and it shows the process of these policies’ affecting the
dynamic transportation - air pollution relationship. Through this, simulation logic is constructed to search
for air pollution policies hereafter.
1, Environmental tax-levy and the dynamics of transportation & air pollution
According to the causal map of Figure 8, when the increase of total air pollution volume induce to
carry out environmental tax-levy, it decreases the allotment ratio of car traffic, daily traffic volume, and
total traffic volume. This increases the average traffic speed and decreases the total air pollution volume
lowing the discharge of CO especially. On the other hand, when environmental tax-levy is less strict due
to a decrease of total air pollution volume, it iterates previous process and in retum will increase the air
pollution volume. Namely, Figure 8 shows the mutual feedback dynamics of transportation & air
pollution through environmental tax variable.
14
2. Affordable exhaust standard and the dynamics of transportation & air pollution
In Figure 8, affordable exhaust standard is set up dividing regulating factors and level by the type of
vehicle. For example, gasoline used vehicles controlled with CO, HC, and overflow of air and light oil
used vehicles with smoke, the permitted limit of smoke is reinforced below 35% from 40% in case of
light oil used vehicles made in 1996 and below 30% in ones made in 1998(Seoul, 2000).
Technology development of exhaust gas reduction is carried out due to the increase of total air
pollution volume, and then it decreases total air pollution volume in the end by lowering the hourly
pollutant discharge. In retum, the decrease of total air pollution volume weakens the policies and
increases it in reverse repeating the previous process. Namely, Figure 8 is about the mutual feedback
dynamics of transportation & air pollution through affordable exhaust standard variable.
3. Preferential treatment for small car and the Dynamics of transportation-air pollution
When we look at Figure 8, preferential treatment for small car increases the ratio of it and helps to
reduce the total volume of air pollution. But the result, the decrease of the total volume of air pollution
weakens the policy and because of this, the total volume of air pollution increases again, repeating the
previous process. Namely, this shows the mutual feedback dynamics of transportation-air pollution
through the preferential treatment for small car variable.
4. Efficient energy use and the Dynamics of transportation-air pollution
When efficient energy use policy is carried out by the increase of the total volume of air pollution, the
ratio of clean-energy used, gasoline used and light-oil used vehicles varies. This changes the volume of
each air pollutant and accordingly the total volume of air pollution varies. The decrease of the total
volume of air pollution as the result, however, weakens the policy and the total volume of air pollution
increases again, repeating the previous process. Namely, this shows the mutual feedback dynamics of
transportation-air pollution through the efficient energy use policy variable.
The causal map for the construction of simulation logic, proposed above, can be looked at like this: If
the policies to lower the volume of air pollution are operated, then they interact with air pollution
variously. So its implication is that it's essential to consider situations long-sightedly and
comprehensively in policy implementation.
15
car onmership
home eats erperson person
Cearowerp crease ate
ee haterat .
Average cere Mrcome passer
oweserae +] bassenmecar
i population
ore averagetip tseou 4
\ ae, teen “a
Average tip
‘ime of tuck
total ip
tig of Truck
‘gasoline tax
volumeliay
vung of tuck
Small car
ratio
gasoline
vehicle ratio
TSP enrission
by vehicles
Figure 8. Causal Loop Diagram for Policy simulation
V. Conclusion
The urban transportation and air pollution has a trade-offs relationship. So it accompanies difficulty to
solve the problem. For this, above all, we need to understand the complex inter-relationship of
transportation-air pollution. Complying with this, we looked at the mutual feedback dynamics of
16
transportation-air pollution through the causal maps as a methodology of system dynamics in this study.
As the first step, we structuralized the causal maps to look at the dynamics of transportation-air
pollution, dividing it by traffic demand traffic volume, by means of transportation, by traffic speed and
by fuels of vehicles. Next, we restructuralized the overall causal map around policy variables to build
simulation logic for the evaluation of the effect of policies. We checked out the mutual feedback
dynamics of transportation- air pollution according to policy variables.
It will be able to scrutinize the inter-relationship of transportation-air pollution more substantially
through the analysis of the dynamics of the two. Also, it will be possible to search for policy alternatives
based on complex interaction system of all factors, not the simple cause-effect relationship.
Forward research, it is required study the simulation more elaborately to discover the dynamic
patterns using modeling of feedback loops based on the analysis of causal map.
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