Dynamics of Urban Structure in Bangkok Based on Employment Cluster and Commuting Pattern

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

DYNAMICS OF URBAN STRUCTURE IN BANGKOK BASED ON EMPLOYMENT CLUSTER AND COMMUTING PATTERN

Varameth VICHIENSAN Lecturer Faculty of Engineering Kasetsart University Phahonyothin Rd, Ladyao, Jatujak Bangkok 10900 Thailand Tel: +66-2-942-8555 ext 1359 Fax: +66-2-579-4575 E-mail: [email protected]

Abstract: Many large cities in the world including Bangkok are now moving toward multi-centric structure in order to tackle with urban problems such as car dependency, traffic congestion, suburbanization, environmental degradation, etc. However, they have achieved at different stage at different pace. Exploring the city structure and its dynamics provides insight on how to go from now. The present paper presents an analysis of urban structure dynamics of Bangkok Metropolitan by considering employment clustering and commuting pattern in the city based on an analytical framework. It is found that Bangkok is in the early stage of polycentric development. However, some locations have high potential to form employment centers, either urban or suburban sub-centers. In addition, classical transportation indicators show that area with good public transport service will be stimulated in forming sub-center by shorter travel time and distance.

Keywords: Employment, Sub-Center, Cluster Analysis, Bangkok

1. INTRODUCTION The rapid population increase, suburbanization, rapid economic growth, motorization, and increase in car dependency are the common urban problems found in the growing cities around the world. However the situation is becoming more severe and difficult to solve in the developing countries where there are several factors that are not controllable, such as disordered development, unstable political climates, etc. Bangkok, the capital of Thailand, is presently facing suburbanization, traffic congestion, and air pollution, which are originated by the poor urban configuration. The objective of this study is to explore the non mono-centric structure of Bangkok based on an analytical framework aiming at understanding the clustering pattern of employment, the relying residential location choice, and the commuting characteristics. The result of the study will imply future land use and transport policy that encourages efficient and sustainable growth of the city. The rest of this paper is structured as follows. It briefly describes the study area in this section and the existing plans and visions in relation toward the multi-centric urban structure in Section 2. The paper then presents an analysis of employment cluster, residence/employment preference, and the employment accessibility in Section 3. Then the influence of change in the urban activities on commuting behavior is presented in Section 4. Finally, Section 5 concludes the paper.

1.1 Urban Development in Bangkok Bangkok Metropolitan Region (BMR) area comprises the central area called Bangkok

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

Metropolitan Area (BMA) and its five adjacent provinces. BMR covers 7,758 sq km. The total population of BMR in 2005 is 10,661,047 or 16.8% of the total population of Thailand. The central area of BMR is centered to almost all urban activities: business district, high to medium density residential areas, as well as industrial area. In 2005, BMR produced a GDP of about 3,139,084 Million Baht, which accounts for about 44.2% of the country's GDP. Since 1960 BMR has been undergoing rapid urbanization and industrialization. The increase in population is due to the development of infrastructures such as road networks as well as real estates. From 1987 to 2000, the number of population has been decreasing in the inner area, but increasing in the middle area. That is, the population density in the inner area decreased from 15.27 to 11.09 thousand/sq km (that is 3.25 to 2.36 million). The outer area has increase in the population density from 0.77 to 1.28 thousand/sq km (which is 0.67 to 1.12 million). Major of travels in Bangkok are made by means of road transport. In 2005, share of private mode is 53% while that of public mode is only 44%. Road and expressway network have played important roles in accommodating the travel demand since they provide convenient service to the destinations. Meanwhile, the public transport service is inadequate. It does not comprehensively cover the whole urban area. People living in sub-urban areas then prefer traveling by private car than using bus. This produces large amount of traffic volume on road and causes traffic congestion. In 2000, there were 4,076 kilometers of road length, which accounts to 58.45 square kilometers. The present expressway length is 175.9 kilometers. Expressways are still being constructed for further 82.3 kilometers, and planned to build 64.1 kilometers after 2009. In terms of public transport, bus is the main mode. Presently there are 404 bus routes in services. In addition, some sub-urban people are commuting to the central Bangkok by using sub-urban railway; a service provided by State Railway of Thailand (SRT). Recently, urban rail transit or metro systems were introduced. In December 1999, an elevated 'Skytrain' metro system (officially called BTS, stands for Bangkok Transit System) was opened. Currently, BTS has two routes, Sukhumvit Line (Green 1) and Silom Line (Green 2). Approximately, BTS carries over 400,000 passengers per day. Five years after BTS opened, a new MRT subway system was opened in July 2004. It connects SRT’s northern long-distance train station, Bang Sue, to its central station, Hua Lamphong. It connects to BTS system at three transfer stations: Mo Chit, Asoke, and Sala Daeng. Although the expressway network together with BTS, MRT, and SRT railway lines have eased the problem a little, much more needs to be developed for the betterment of city living.

2. POLICIES ENCOURAGING EMPLOYMENT POLYCENTRISM The heavy concentration of population in Bangkok Metropolitan Region has made it one of the most populated cities and one of the most active economic centers in South East Asian Region. In the past, suburbanization as well as ad-hoc land development has led Bangkok grown disorderly. The unplanned urban sprawl currently in progress causes not only traffic congestion, but various problems relating to the urban living environment. These include mix of conflicting use of residential and industrial, insufficient provision of public services, and the environmental deterioration. The concerned agency has put large efforts to devise both land use and transportation instruments to tackle such problems, including the metropolitan spatial planning to be described next.

2.1 Metropolitan Spatial Plan Previous studies such as Rujopakarn (2003) indicated that traffic problems in Bangkok were

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007 originated from inefficient master plan, inefficient planning and design standards, ineffective land-use control, unstructured hierarchy of road network, as well as inefficient public transport system. In a bigger picture, Thailand has become automobile-dependent during the past transportation plans and policies. Road-based transports had obtained top priority, taking almost all of the budgets available for transport infrastructure development. However, less attention is given to land use regulation or land use control to structure the city in accordance with the master plan. The first revision of Bangkok City Planning, or so-called the Comprehensive Plan, was devised in 1999. Recently, the plan was revised by adding changes in the circumstances since the first revision. Now, its second revision is now effective; so called the Ministerial Regulation on Bangkok Comprehensive Plan BE 2006 which regulates the use of land in the Bangkok.

Figure 1 Land use designation in Bangkok metropolitan plan 2006 Comparing with the previous plan, land designation was changed in some parts of the city; reflecting increased development. Many of the changes are due to transportation development. Transportation demand is forecasted from 2002 to the next 20 years. Congestion in the inner area, i.e., the area surrounded by Ratchadapisek middle ring road, is reportedly becoming more severe. The average speed reduces from 18 km/hr in 2002 to 14 km/hr in 2009, and 12 km/hr in 2022. Although roads are becoming more congested, people still prefer traveling by private cars. Share of public transport reduces from 45% in 2002 to 40% in 2009, and 38% in 2022. It is, therefore obvious that Bangkok needs a proper set of countermeasures to alleviate the traffic congestion problems. Land use regulation and the related measures must be carefully considered and applied. The measure may be to provide transport infrastructure such as urban rail transit. In this case, understanding its impact to urban development will provide good information for other policy measures.

2.2 Visions on Employment Center Taking into consideration the present urban structure of the BMR area, which takes a so-called “ribbon urbanization pattern” sprawling along major arterial roads, Thailand may

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007 be positioned somewhere in between the first and the second groups with the cost of trips around 10 percent of GDP. In terms of private account, the statistics in Table 1 shows that households are spending more on transportation, i.e., from 12.8% of income in 1995 to 21.7% in 2005. Table 1 Average household expenditure Items 1995 2004 Housing 22.4% 20.4% Transportation and Communication 12.8% 21.7% Other 64.8% 57.9% Source: National Statistical Office

In order to reform the BMR urban area towards a more low-cost structure particularly in the situation where oil price is constantly hiking, the urban sprawl should be put an end and a rail-based polycentric structure should be created so that public transport by rail should be the dominant mode of transport networking multiple polycentric sub-centers with the lower cost of trips for the BMR community as a whole. The urbanization of individuals and ad-hoc land development causes pertinent congestion and deteriorates the living environment in Bangkok Metropolis. Therefore, the realignment of the urban structure and the development of sub-center in the suburbs must be an urgent issue for the well-ordered growth of Bangkok metropolis, and the transportation plan of the sub-center development should be discussed with authorities related to the city planning sector (BMA and DPT) and transportation sector (OTP and SRT) because a close linkage of railways and road networks is a primal step to secure the accessibility to the sub-center area.

2.3 Example of Planned Urban Sub-centers

2.3.1 Urban Sub-centers New urban sub-centers are expected to be developed within 10 km radius in the proximity of MRT stations, Office of Transport and Traffic. Policy and Planning (2006). Urban sub-centers function to assume reassigned urban functions within Expanded CBD by absorbing new demand for “producer services” and creating new urbanity accessible to amenities and urban lifestyles. Potential candidate locations are Bang Bamru, BSTC, Chatu Chak, and Makkasan. It is of the strategic importance to develop urban sub-centers in Bang Bumru and Chom Thong in the west bank of Chao Phraya River in order to reduce the cross-river traffic demand that requires more river crossings.

2.3.2 Suburban Sub-centers New suburban sub-centers are also expected to be developed within the commutable distance of 10-30 km radius in the proximity of MRT stations, Office of Transport and Traffic. Policy and Planning (2006). Suburban sub-centers function chiefly as dormitory towns to: massive provision of residential complex; provision of self-sufficient livelihood infrastructure and facilities including schools, parks, sports and recreation centers, etc.; Convenient rail transit system for commuting to CBD or urban sub-centers; Station-front plaza development conveniently transferable to local transport modes and accessible to livelihood functions such as shopping center and malls, banks, amusement facilities, etc.; and Introduction of selected compatible urban functions such as “back offices”, “communication factories”, etc. to enable

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007 the proximity between working and living places. Potential candidate locations are as follows: Phuttha Monthon, Nonthaburi, Rat Burana, Phra Khanong, Bang Kapi, Bang Khae, Bang Bon, Samrong, Don Muang (Chaeng Watthana Government Center), Taling Chan, and Lat Krabang – Suvarnabhumi Aerotropolis.

3. DYNAMICS OF EMPLOYMENT CONCENTRATION To examine the urban configuration in terms of employment concentration, there are techniques to determine the employment location based on the city development pattern. Recently, the discrete choice modeling approach have obtained interest in the location analysis setting such as Miyamoto et al. (2004), which is to determine with consideration of land use and transportation interaction explicitly. In this study, in order to determine how the employment concentration is related with the work trip pattern, the cluster analysis framework is employed, which follows the approach described in Alpkokin et al. (2005b).

3.1 The Dataset The employment data used in this study is the same dataset used by the Office of Transportation Policy, Office of the Commission for the Management of Land Traffic (2000). The socioeconomic data is the same input to the official transportation model for Bangkok, so-called e-BUM, which is based on the proprietary software, named CUBE, and has been employed in the real transport planning for several years, Office of the Commission for the Management of Road Traffic (1997). The multimodal transportation network data is consisted of intensive highway network, railway network, ferry links, and non-motorized mode. Table 2 summarizes the data used in this study. The population total is decreased from 1995 substantially. This may be due to the overestimation of the latent population in 1995, so the data was adjusted accordingly in the revision. In addition, in the revision, many areas having rapid growth of the economic activities or travel demand were also refined into smaller zones; resulting in the larger number of traffic analysis zones in the 2005 dataset. Table 2 Data summary 1995 2005 Total population 11,452,000 10,661,047 Total employment 6,349,705 5,979,722 Traffic analysis zones (internal) 505 584 Size of study area (km2) 7,732 7,732 At a glance, Bangkok metropolitan has been centered at the middle of the study area, where population and employment are densely located. In the past decade, suburbanization can be observed as shown by spreading out of population and employment density in Figure 2 and Figure 3 respectively.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

(a) 1995 (b) 2005

Population Density 1995 0.00 to 325.00 (68) 325.00 to 900.00 (76) 900.00 to 3147.00 (88) Population Density 2005 3147.00 to 9020.00 (107) 0.0000 to 410.0000 (68) 410.0000 to 1240.0000 (73) 9020.00 to 19400.00 (109) 1240.0000 to 4000.0000 (93) 19400.00 to 1000000.00 (136) 4000.0000 to 7084.0000 (95) 081624 7084.0000 to 15570.0000 (126) Ki l ometers 15570.0000 to 100000.0000 (129) 04812 Miles Figure 2 Population density

(a) 1995 (b) 2005

Employment Density 1995 0.00 to 135.50 (71) 135.50 to 390.00 (77) 390.00 to 1550.00 (94) Employment Density 2005 1550.00 to 4700.00 (107) 0.0000 to 123.8000 (70) 4700.00 to 13000.00 (126) 123.8000 to 380.0000 (79) 13000.00 to 1000000.00 (109) 380.0000 to 1462.4000 (95) 081624 1462.4000 to 6240.0000 (138) 6240.0000 to 20000.0000 (130) Kilometers 20000.0000 to 1000000.0000 (72) 04812 Figure 3 Employment density Miles

3.2 Employment Clusters In order to determine the employment cluster in the study area, the logarithmic employment density is plotted against the rank size; the gross employment density is on the vertical axis and the rank is on the horizontal axis, Alpkokin et al. (2005a). To identify cluster range, there is a tendency for grouping the zones into four clusters, or tiers, but the actual number will arise from the data depending on the size of the city; this study also use four-cluster classification. To do this, the graph is visually inspected and divided into parts indicated by obvious breaks. In case of Bangkok in 2005, as shown in Figure 4, roughly the first employment cluster is considered for zones with high employment density locating in the old core of the city; while the fourth cluster is cut at the slope change at the lower end of the graph. The second and the third clusters are obtained by dividing the middle graph approximately by half. To be exact three cut points for four-cluster classification are the logarithmic value of the zonal employment density of 9.5, 7.0, and 5.0 respectively.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

12 Cluster 1 10 Density) Cluster 2 8

6 Cluster 3 (Employment 4 ln Cluster 4 2

‐ 1 151 301 451 Rank of Zones

Figure 4 Classification of Bangkok employment centers in 2005 In addition, the change in employment location patterns as well as the emergence of new sub-centers may be examined by plotting the graph of different time points. In this case, the rank size of employment density in 1995 and 2005 are plot as shown in Figure 5. It is obvious that there is small increment in the previously dense area in the city center but large increment in the outer zones where the previous employment was not dense. This may be recognized that Bangkok Metropolitan has been decentralizing. Such interpretation is intuitive as there are huge developments spread out the city, both commercial and residential.

12 1995

10 2005 8

ln (Employment Density) 2

0 1 151 301 451 Rank of Zones Figure 5 Comparison of rank size distribution of Bangkok employment zones The cluster maps of employment in the two years are shown in Figure 6. Due to the decreased employment total in the city, some zones previously classified as Cluster 1 are changed to lower density Cluster 2 in the later year. It is, however, obvious that Bangkok Metropolitan has generally a monocentric structure, which has big core in the middle and is surrounds by lower density area. The 2005 map indicates that there are clearly certain high density employment centers (Cluster 1) spreading across the large middle core area. These are surrounded by lower density employment zones (Cluster 2 and 3), implying that they have potential to form employment subcenter.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

(a) 1995

CLUSTER 1995 1 (105) 2 (264) 3 (135) 4 (80) 081624 Kilometers (b) 2005

CLUSTER05 1 (110) 2 (260) 3 (126) 4 (88) 04812 Miles Figure 6 Employment clusters in 1995 and 2005 Comparing the change of statistics between 1995 and 2005 data, shown in Table 3, despite of the given decreased employment total, the city is again considered being sprawled out from the previously dense area. Share of the number of zones in Cluster 1 is decreased while that of Cluster 2 is increased. Those zones in Cluster 2 are located in the medium-dense area within the inner ring road of Bangkok. Next, in order to explore the spatial extent of the commuting trips attracted to each employment center in the city, it is well known to consider the classical transportation indexes such as Vehicle Kilometer or Mile Travel (VKT or VMT), Mode Share, or Trip Length Frequencies at some representative zones picked up from each cluster at different locations over the study area. However, it is also wise to examine the employment specific preference function and will be presented next.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

Table 3 Change of Employment in Each Cluster 1995 2005 Change Total Employment 6,349,705 5,962,497 -6.1% Cluster 1 Employment 1,764,846 1,585,323 -10.2% Share over total 27.8% 26.6% Number of zones 105 110 5 Cluster 2 Employment 3,102,130 2,978,931 -4.0% Share over total 48.9% 50.0% Number of zones 264 260 -4 Cluster 3 Employment 1,124,646 1,013,341 -9.9% Share over total 17.7% 17.0% Number of zones 135 126 -9 Cluster 4 Employment 358,083 384,902 7.5% Share over total 5.6% 6.5% Number of zones 80 88 8

3.3 Employment Preference Functions A more analytical way of grasping the residential location preferences for a given employment center is to plot the destination-specific employment preference function, based on a form of the intervening opportunity model, Black et al. (1993). The estimation of the shape of the zonal preference functions requires information about: the zonal number of resident workers, the zonal number of job opportunities, the destination-origin pattern of traffic, and the inter-zonal transport impedance. Estimation of the raw preference function for each employment zone can be summarized, Alpkokin et al. (2005b), as follows: • Residential worker (destination) zones are ranked in order of increasing distance from the employment zone (origin zone). • The cumulative numbers of labor-force workers are calculated at increasing distance from the employment zone and these are expressed as a proportion of metropolitan total. • From the D/O data, the number workers residing with destinations at increasing distance from the employment zone is set out. • The D/O flows are expressed as a proportion by residential worker (destination) of the zonal trips attractions to the employment zone. • The proportions are plotted as a graph. • Finally, a quadratic function (Y=aX2+bX+c) is estimated for curve fitting. Other function form may also be employed. For each employment zone, residential zones are ranked according to increasing distance, or better, transportation travel time, by either car or public transportation, or a weighted combination of the two away from that zone. The number of residential workers living in each zone is a proxy for housing opportunities. By plotting the cumulative distribution of residential workers reached, a “housing” opportunity surface around that employment zone is constructed. Steep gradients imply a nearby choice of residential location; shallow gradients around a sub-center imply a broader, metropolitan-wide, spatial labor market. Figure 7 shows the raw preference function obtained by plotting the data of zone 129 Sathon. It is located in the central area, so the graph is relatively flat.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

Plot of Employment Location Specific Preference Function for Zone 129 Sathon 1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2 Y [Cum. Pro. of Workforce Captured] Workforce of Pro. [Cum. Y

0.1

0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 X [Cumulative Proportion of Workforce Reached]

Figure 7 Employment preference function obtained from the raw data Among 584 internal traffic analysis zones in Bangkok, 27 different zones in the four clusters are selected to examine their location specific employment preference function, shown in Figure 8. Zones in the central area have high density employment, i.e., Cluster 1, and attract many workers from across the metropolitan area, resulting in flat preference function. These zones include Bang Rak, Sathon, Klong Toei, etc. Similarly, zones in the inner dense area of Bangkok, which are also in Cluster 1, but attract nearer people, so resulting in steeper graph. These include Phaya Thai, Phra Nakhon, Huai Kwang, etc. In addition, there are many zones that are emerging sub-centers where the graph is relatively steep and they are classified in Cluster 1. These include Chatu Chak, Don Muang, Pra Pradaeng, etc. On the other hand, there are zones having lower density, i.e., Cluster 4, but the preference graph is relatively steep. These are the zones of the satellite town such as Muang Nakorn Pathom, Muang Samut Sakorn, etc.

Cluster IV Satellite Centers

Cluster II, III Emerging Urban & Suburban Subcenters

Cluster I City-Wide Center

Cluster I CBD

Figure 8 Employment preference functions in 2005

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

In terms of changes over time, five locations are selected to observe the change of employment preference between 1995 and 2005, and the functions are estimated in quadratic form, as shown in Figure 9. The dotted lines are the 1995 data and the full lines are 2005. For Sathon and Bang Rak, which are the city centers, the 2005 and 1995 lines are relatively parallel; implying that the central area is still growing and attracting people living farther away. However, for Don Muang, Minburi, and Chatu Chak, the 2005 graphs are relatively steeper than 1995; implying that their workers are living nearer to their workplace. Moreover, this is also obvious for a remote town such as Muang Nakornpathom where its center is growing and attracting workers from the nearer residents.

1 Sathon 95 Sathon 05 0.8 Bang Rak 95 Captured

Bang Rak 05 0.6 Don Muang 95 Workforce

Don Muang 05 of 0.4 Minburi 95 Pro. Minburi 05

Cum. 0.2 Muang Nakornpathom 05 Muang Nakornpathom 05 0 Chatu Chak 95 0 0.2 0.4 0.6 0.8 1 Chatu Chak 05

Cumulative Proportion of Workforce Reached

Figure 9 Dynamic of employment preference at some locations

3.4 Employment Accessibility Accessibility is generally defined as some aggregate measure of the size and closeness of activity opportunities of a given type to a particular location. In case of employment opportunity, a common measure is expressed as

Aij=×∑ E f() impedance ij j

where Ai is the employment accessibility of zone i , E j is the number of employment or workforce available in zone j . In this study the impedance function between zone pair is defined as the distance-decay function of generalized travel cost between zones on a particular mode, i.e., f =−exp(costij ) .

Figure 10 and Figure 11 show the employment accessibility in Bangkok Metropolitan on private (car) and public (bus, taxi, rail, ferry) transport modes in year 1995 and 2005 respectively. Generally it is obvious that employment accessibility increases for both modes particularly along the major road corridors to the north and the east. Of particular interest is the large increase of accessibility in the area along the urban railway lines: BTS skytrain and MRT subway, which gives rise to the potential to form urban sub-centers. Similarly, the outer area such as Minburi, which was in cluster 4 as discussed earlier, has much increase in the job accessibility and has good prospect to form as a sub-urban sub-center.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

1995 2005

CAR95 CAR05 0.00 to 0.20 (84) 0.00 to 0.03 (83) 0.20 to 4.54 (82) 0.03 to 0.93 (83) 4.54 to 28.00 (84) 0.93 to 8.00 (84) 28.00 to 77.00 (83) 8.00 to 35.50 (83) 77.00 to 170.00 (84) 35.50 to 97.80 (84) 170.00 to 310.00 (83) 97.80 to 232.00 (83) 310.00 to 10000.00 (84) 232.00 to 10000.00 (84) Road Network Road Network Minor Road Minor Road Maj or Road Maj or Road Expressway Expressway 0246 0246 Miles Miles Figure 10 Employment accessibility by private transport in 1995 and 2005 1995 2005

PUB95 PUB05 0.00 to 0.01 (206) 0.00 to 0.01 (141) 0.01 to 0.14 (53) 0.01 to 0.03 (30) 0.14 to 2.70 (65) 0.03 to 1.30 (79) 2.70 to 16.20 (65) 1.30 to 74.00 (83) 16.20 to 67.90 (65) 74.00 to 410.00 (84) 67.90 to 280.00 (65) 410.00 to 1480.00 (83) 280.00 to 10000.00 (65) 1480.00 to 100000.00 (84) Road Network Road Network Minor Road Minor Road Maj or Road Maj or Road Expressway Expressway 0246 0246 Miles Miles Figure 11 Employment accessibility by public transport in 1995 and 2005

4. INFLUENCES TO COMMUTING BEHAVIOR Although the finding presented in the previous section shows that the city is more or less growing into polycentric structure, Bangkok in the present day is still in the early stage of development. These can be seen by the fact that the city is continuously sprawling out; suburbanization. There are large development both in terms of public infrastructure and private establishment. This resulted in the severe traffic congestion due to the huge amount of cross-town travel in the peak hour. This section examines to what extent the change in city structure affects the change in the travel pattern, especially the journey to work.

4.1 Travel Time of Work Trip Due to the recovery of Thai economy with rapid growth, there are a lot of developments over the metropolitan area, which have unavoidably generated large amount of travel demand and traffic volume on road network. Moreover, many people are moving out to live in the suburb, where new and better housings are available, and traveling to work for longer distance, either by car or bus on the road network. However, the resulting congestion again gives rise to the travel time. Table 4 shows that the metropolitan-wide average travel time to work has increased substantially from 36.4 minutes in 1995 to 42.7 minutes in 2005; implying that people may live farther away and may drive in more congested road.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

Table 4 Change of the metropolitan average commuting time Average Travel Time to Work (minutes) 1995 36.4 2005 42.7

In addition, it is worthwhile to examine the travel time frequency distribution change between 1995 and 2005, in Figure 12. Statistically, the mean travel time is larger and the graph is shifted to the right; showing that most people are spending longer time in traveling to work and the travel time has more variation among the travelers.

50%

1995 40% 2005

30%

20%

Percentage of Trip (%) 10%

Time Intervals (min)

Figure 12 Travel time frequency distribution of work trips Next, the three employment zones in Figure 9 are selected for further examination by looking at the travel time frequency distribution of work trips specifically at these locations, shown in Figure 13.

25%

Chatu Chak 20% Minburi Bangrak 15%

10%

5% PercentageTotalof Trip (%) 0%

Trip Time (Minutes)

Figure 13 Trip length frequency distribution of work trips attracted to three sub-centers

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

The graph is connected to be continuous for the ease of presentation. Let consider Chatu Chak (Cluster 2), an employment center locating 10 kilometer north to the old core CBD. The employment preference analysis has showed earlier that Chatu Chak is emerging to be an urban sub-center of Bangkok. It is shown here that most of workers in Chatu Chak travel to work for about 30 minutes with relatively low variation. On the other hand, Bangrak (Cluster 1), which is the city center, has larger travel time variation; implying that workers are coming from across the city and passing through the congested roads. However, Minburi (Cluster 4), a potential suburban sub-center locating 25 kilometers east to the city center, is attracting people coming to work by traveling quite long; over 60 minutes with the lowest deviation among the three locations. In the other words, workers may prefer to live far away and commute to work in less congested traffic in the suburban area even taking longer time.

4.2 Modal Share of Public Transport In addition to the journey-to-work travel time, this section examines how the change of urban structure toward a polycentric city has influence on public transport usage. The modal share of public transport at some employment zones are calculated and shown in Table 5. Table 5 Change of public transport share and employment cluster at some locations Zone Name % Public 95 % Public 05 Cluster 95 Cluster 05 4 Phra Nakhon 35.9% 39.2% 1 1 79 Bang Rak 38.1% 40.0% 1 1 176 Bang Kapi 44.1% 35.7% 1 1 345 Phra Pradaeng 38.6% 39.2% 1 1 154 Chatu Chak 34.8% 45.9% 2 2 159 Don Muang 27.2% 30.2% 2 2 205 Phra Khanong 37.5% 42.1% 2 2 216 Suan Luang 52.3% 42.0% 2 2 356 Muang Samut Prakarn 38.3% 35.1% 2 2 162 Don Muang 36.9% 44.0% 3 3 302 Bang Khun Thian 36.1% 32.0% 3 3 389 Muang Nonthaburi 37.3% 38.1% 3 3 428 Muang Pathum Thani 33.4% 34.9% 3 3 257 Latkrabang 42.2% 32.0% 4 3 250 Minburi 30.5% 36.6% 4 4 442 Lam Luk Ka 33.3% 30.2% 4 4 447 Khlong Luang 32.7% 28.9% 4 4

Although the metropolitan-wide average travel time is increased, the public transport modal share is increased in some locations. For Cluster 1 zones, Phra Nakhon and Bang Rak, which are the inner zones, has substantial increase in public mode share possibly due to the improved bus service in the inner area while Bang Kapi and Phra Padaeng, which are the outer zones, have lower share of public transport in the later year 2005. This is due to the rapid increase in employment sector but the public transport is not well provided, so this has induced more use of car. Similarly, public transport mode share in 2005 is larger than in 1995 for Don Muang and Minburi, which have potential for sub-center formation. In addition, it is more interesting to see Chatu Chak, discussed previously. Mode share for work trip is increased from 34.8% to 45.9% in 10 years, similar to Bang Rak. These two zones are the end terminal of the urban railway line, named BTS Skytrain. This shows that employment centers having better choice of travel will eventually attract more workers to come to work in. As the number of attracted people is increased and moved closer to the workplace, the polycentric structure will become more realized.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.6, 2007

5. CONCLUDING REMARKS

This paper has presented an empirical study of dynamics of employment location in Bangkok Metropolitan within an analytical framework by considering the employment clusters, the location-specific employment preferences, and the employment accessibility. It is found that Bangkok is presently in its early stage of polycentric development, in the other word; the city is currently rather monocentric. However, some certain locations have high potential to form employment centers, either in the inner or in the outer area; i.e., they will become the urban and suburban sub-centers at their mature age. In addition, the classical transportation indicators such as travel time frequency distribution and public transport modal share are examined and presented. It is found that the area with good public transport service, either by bus or rail services, will be more attractive to both employer and employee, which will stimulate formation of employment center rapidly. Lastly, similar some Asian cities such as Hanoi or Jakarta, Bangkok have been developing in its changing era; from road-based to railway-based development. Previously the travel within the cities was solely based on road transport, making the city sprawl out and making a large amount of cross-town traveling, especially in rush hours. Care must be taken to develop those high potential areas to shift people from road to rail transport because they tend to stay and work in a convenient place to travel to/from work. This will be the key to the success of polycentric development, which will finally lead to a sustainability development where energy consumption is less, air pollution is alleviated, and eventually the quality of life of people is improved. This is likely to be the same situation for those Asian cities.

ACKNOWLEDGEMENTS This study is a part of the International Cooperative Research Activity (ICRA) Project entitled Dynamics of Poly- centric Employment Formation in East and Southeast Asian Cities under the Eastern Asia Society for Transportation Studies (EASTS). The author wishes to express his sincere gratitude to all project members for their great contribution to the success of the study especially to Professor Dr. Yoshitsugu Hayashi (Nagoya University), Professor Dr. John Black (University of Sydney), and Dr.Pelin Alpkokin (Nagoya University).

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