Published in: Proceeding of 9th SENVAR / 2nd ISESEE, Shah Alam, Malaysia, December 2008

Transcription

1 Evaluation on Lighting Condition and Visual Legibility of Road Surfaces and Traffic Signs in Bandung City Mangkuto, R.A.; Soelami, F.X.N.; Soegijanto, R.M. Published in: Proceeding of 9th SENVAR / 2nd ISESEE, Shah Alam, Malaysia, December 2008 Published: 01/01/2008 Document Version Accepted manuscript including changes made at the peer-review stage Please check the document version of this publication: A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. The final author version and the galley proof are versions of the publication after peer review. The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication Citation for published version (APA): Mangkuto, R. A., Soelami, F. X. N., & Soegijanto, R. M. (2008). Evaluation on Lighting Condition and Visual Legibility of Road Surfaces and Traffic Signs in Bandung City. In Proceeding of 9th SENVAR / 2nd ISESEE, Shah Alam, Malaysia, December 2008 (pp. 1-7). Shah Alam, Malaysia. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 13. Jan. 2019

2 EVALUATION ON LIGHTING CONDITION AND VISUAL LEGIBILITY OF ROAD SURFACES AND TRAFFIC SIGNS IN BANDUNG CITY Rizki Armanto 1, F.X. Nugroho Soelami 2 and R.M. Soegijanto 3 1, 2,,3 Department of Engineering Physics, Institut Teknologi Bandung, Bandung, INDONESIA 1 armanto@tf.itb.ac.id, 2 nugroho@tf.itb.ac.id, 3 soegi@tf.itb.ac.id ABSTRACT: As the capital city of West Java Province, Bandung has been growing fast nowadays, which increases the number of road users, during day and nighttime. In order to assure road users can drive safely at nighttime, good visual condition of the road surfaces and their traffic signs is required. The main objective of this research is to evaluate lighting condition and visual legibility in some roadways in Bandung, by determining average luminance, overall uniformity, longitudinal uniformity, and luminance coefficient of road surfaces and traffic signs, and comparing with the minimum criteria. Software was used to simulate the lighting condition of the roadways and to optimize the lighting parameters. Laboratory experiments were conducted to investigate visual legibility of some common traffic signs, based on luminance contrast of the traffic signs material. Generally, lighting parameters of the observed roadways had not fulfilled the minimum standard recommended by the Illuminating Engineering Society of North America. Concrete surface was also found more reflective (average luminance coefficient of 0.05 cd/m 2 /lux) than asphalt one (0.04 cd/m 2 /lux). Laboratory results show that most traffic signs in Bandung were made of advertising grade material, whose average luminance contrast values ranged from 2.33 to 2.85, which were still below the American Association of State Highway and Transportation Officials M standard which states traffic signs at least must be made of engineering grade material. Keywords: roadway lighting, road surface, visual legibility, traffic signs 1. INTRODUCTION As the capital city of West Java Province, Bandung has been growing fast nowadays, which increases the number of road users throughout the day. In order to assure road users can drive their vehicles safely at nighttime, good visual condition of the road surfaces and their traffic signs is required. Human eyes tend to be attracted with bright objects in visual field. The legibility of an object does not only depends on variation of condition and physical appearance of the object, but also depends on the environment where the object is located. The distance between the object and observers (vehicle drivers), is also need to be considered. Visual performance of road surface is determined by evaluating its average surface luminance L av (light intensity from a specific surface per projected surface area viewed from a certain angle, in cd/m 2 ), overall uniformity U 0 (minimum luminance per average luminance), longitudinal uniformity U 1 (minimum luminance per maximum luminance over a specific line) [Simons, 2000], and luminance coefficient q (luminance per illuminance at a specific point, in cd/m 2 /lux). Those parameters are influenced by many factors, particularly the surface material type and distribution of light coming from the road luminaires. For the case of traffic signs, legibility is determined by evaluating luminance contrast between the object and its background, and also field luminance where the object is actually located. The main objective of this research is to evaluate lighting condition and visual legibility at nighttime in some roadways in Bandung, i.e. Ir. H. Juanda, Pasir Kaliki, Wastu Kencana, and BKR Streets, by determining the above mentioned parameters of the road surfaces and traffic signs, and comparing with the minimum criteria. Laboratory experiments were conducted to investigate visual legibility of some common traffic signs material, i.e. advertising grade, engineering grade, high intensity grade, and diamond grade, based on luminance contrast of the traffic signs materials. Field measurements were conducted as well to determine luminance contrast of some traffic signs which exist in some locations in Bandung.

3 2. EVALUATION ON LIGHTING CONDITION OF ROAD SURFACES 2.1 Measurement Prior to measure luminance of road surface, measuring points must be determined first on the surface. The calculation grid is adapted from the International Commission of Illumination (CIE) [Bommel, 1980], as illustrated in Figure 1: Figure 1: Calculation grid plan for surface luminance measurement In Figure 1, s is distance between adjacent road luminaire poles, w is lane (one way traffic flow) width, and d is distance between adjacent columns in the calculation grid. For s 50 m, d is chosen so that there are 10 columns in the grid. For s > 50 m, the number of columns must be chosen so that d 5 m. Space between adjacent points in a column is w/6. The observer point is positioned 60 m from the nearest column, w/4 from the nearest roadside, and at height of 1.5 m [Bommel, 1980]. In-situ measurements were conducted for each measuring points by using luminance-meter which was attached with a FOV1 telescope to limit the viewing angle to about 6 [Armanto, 2006]. Illuminance at each points were also measured to determine the luminance coefficient, which is the ratio of luminance to illuminance at a specific point on the road surface [Bama, 2007]. Measurements were conducted at nighttime in Ir. H. Juanda Street (two lanes, entire surface made of asphalt), Pasir Kaliki Street (two lanes, asphalt), Wastu Kencana Street (one lane, asphalt), and BKR Street (two lanes, each has asphalt and concrete surface). The results are tabulated in Table 1. Table 1: Measurement results of the road surfaces Roadways L av (cd/m 2 ) U 0 U 1 q av (cd/m 2 /lx) Ir. H. Juanda (lane 1) Ir. H. Juanda (lane 2) Pasir Kaliki (lane 1) Pasir Kaliki (lane 2) Wastu Kencana BKR (lane 1, asphalt) BKR (lane 1, concrete) 0.04 BKR (lane 2, asphalt) BKR (lane 2, concrete) 0.05 Measurement results show that most of the lighting parameters of the observed roadways had not fulfilled the minimum criteria recommended by the Illuminating Engineering Society of North America (IESNA), which are tabulated in Table 2 [IESNA, 2000]. Average luminance coefficient values were found

4 greater for concrete surface (q av = 0.05 cd/m 2 /lux), compared with that for asphalt one (q av = 0.04 cd/m 2 /lux). It is concluded that concrete surface are slightly more reflective than asphalt one, thus gives higher surface luminance at night. Table 2: IESNA minimum criteria for road lighting parameters Roadway Classification Major Collector Area Classification L av (cd/m 2 ) U 0 U 1 Commercial Intermediate Residential Commercial Intermediate Residential Source: (IESNA, 2000) 2.2 Simulation and Optimization DIALux 4.1 software was used to model the existing lighting condition and to optimize the parameters. Ir. H. Juanda and Pasir Kaliki Streets are both classified as major roadways at intermediate area, Wastu Kencana Street is classified as collector roadway at commercial area, while BKR Street is collector roadway at intermediate area. Different approaches were used in the simulation to optimize the parameters. For Ir. H. Juanda Street, the distance between adjacent luminaire poles was decreased from 44 m (existing) to 27 m, while the luminaire poles were kept positioned on street median. For Pasir Kaliki Street, the distance between adjacent luminaire poles was decreased from 43 m to 28 m, and luminaire poles were added on side of lane 2 to become opposite configuration. For Wastu Kencana Street, the distance between adjacent luminaire poles was decreased from 36 m to 27 m, while the poles configuration was kept staggered. For BKR Street, luminance coefficient were increased by paving the entire surface with concrete, as well as decreasing distance between adjacent luminaire poles from 49 m to 33 m. The optimized parameters are tabulated in Table 3. Table 3: Optimized parameters by simulation of the road surfaces L av Roadway (cd/m 2 ) U 0 U 1 Ir. H. Juanda (lane 1) Ir. H. Juanda (lane 2) Pasir Kaliki (lane 1) Pasir Kaliki (lane 2) Wastu Kencana BKR (lane 1) BKR (lane 2) It is found that average surface luminance may be enhanced by simply using lamps with higher light output, or by changing the surface material with more reflective one. However, luminaire poles spacing and configuration is the most significant factor which determines uniformity, since a shorter distance between adjacent poles will create more uniform illuminance distribution on the surface, thus give a better overall and longitudinal uniformity. 3. EVALUATION ON VISUAL LEGIBILITY OF TRAFFIC SIGNS Experiments to investigate the visual legibility of traffic signs were conducted in two methods, i.e. laboratory and field measurements. In both methods, luminance contrasts of the traffic signs coating

5 material were evaluated. It is desired to have a relatively high luminance of the traffic signs, compared to the surrounding background. In other words, high value of luminance contrast might give high quality of visual legibility. 3.1 Laboratory Measurement Laboratory measurements were conducted for five types of traffic signs material, i.e. diamond grade (one sample), high intensity grade (one sample), engineering grade (two samples), advertising grade (two samples), and a sample which was mixture of engineering and advertising grade. The traffic sign was positioned in a dark room and was illuminated by a single 150 watts halogen lamp. To determine luminance contrast, five points (center, upper, lower, right, and left corner) on the traffic signs surface were viewed using FOV1 telescope, while the luminance values L o (in cd/m 2 ) were collected. Adjacent background luminance L b (in cd/m 2 ) was measured as well. Light intensity produced by the lamp was also varied by setting the power to 1/8, 1/4, 1/2, and full output [Pradana, 2007]. Figure 2: Equipment setup for laboratory measurement The entire measurement data were averaged and analyzed to determine the luminance contrast of the traffic sign, which can be defined as the ratio of difference between (L o and L b ) to L b. The range will be between 1 and 0 if the objects are darker than their background, and will be between 0 and if the objects are brighter than their background [Cuvalci, 2000]. The results are tabulated in Table 4. Table 4: Laboratory measurement results Material type Average Luminance Contrast Diamond grade 9.00 High intensity grade 6.69 Engineering grade (sample 1) 4.26 Engineering grade (sample 2) 3.76 Advertising grade (sample 1) 2.85 Advertising grade (sample 2) 2.33 Mixture of engineering and advertising grade 3.00 The measurement results clearly show that the diamond grade material had the highest luminance contrast, while advertising grade had the lowest one. According to the American Association of State Highway and Transportation Officials (AASHTO) M standard, which is adapted by Indonesian Department of Transportation, material for traffic signs should at least be made of engineering grade coating [Dephub RI, 2007].

6 3.2 Field Measurement Field measurements were conducted in some roadways in Bandung, i.e. Jend. A. Yani and Jend. Gatot Soebroto Streets. Types of the traffic signs material were unknown, so the luminance contrast values from the field measurement were compared to those from the laboratory one. The measurement setup is shown in Figure 3. Figure 3: Equipment setup for field measurement However, relatively low background luminance is needed to reach similar condition with the experiment in dark room. This was unfortunately difficult, since there were a lot of bright billboards and light from the surrounding area, which distracted the focus of sight and greatly reduce the traffic signs legibility. In some cases, background luminance values were even greater than the object ones, thus resulted in negative contrast values. Table 5 shows the measurement results. Table 5: Field measurement results L o L b Traffic sign (cd/m 2 ) (cd/m 2 ) C Note No turn right for trucks Billboard near sign No turn left Billboard near sign No trespassing Billboard near sign No turn right for cars No billboards near sign No turn right for cars No billboards near sign Based on measurement data without billboards, the no turn right for cars sign s material could be classified as advertising grade, since the contrast luminance values were quite near the ones that were obtained from the laboratory experiment. Also, since the no turn right for cars sign s material is typically used in Bandung, it may be assumed that most traffic signs in the city are made of advertising grade material, which is below the AASHTO standard requirement. It is obvious that in order to achieve good legibility of traffic signs, surrounding billboards and any light source whose luminance are significantly greater than the traffic signs luminance, should be removed. Good understanding and cooperation between the city government, police, and advertisement bureaus are required to avoid the visual pollution, thus could give better and safer visual environment in the city. 4. CONCLUSION Generally, lighting parameters of the observed roadways have not fulfilled minimum standard recommended by the Illuminating Engineering Society of North America. From the software simulation, it was found that the parameters, particularly the uniformity, could be improved by decreasing distance

7 between adjacent luminaire poles. Concrete surface was also found more reflective (q av = 0.05 cd/m 2 /lux) than asphalt one (q av = 0.04 cd/m 2 /lux). Laboratory experiments results show that diamond grade material had the highest value (C = 9.00), while advertising grade material had the lowest one (C = 2.33~2.85). Field measurements were also conducted, whose results showed that most traffic signs in Bandung were made of advertising grade type, which were still below AASHTO M standard which requires traffic signs at least must be made of engineering grade material. However, installment of billboards near traffic signs in roadways should be avoided, for it may create visual pollution which greatly reduces the visual legibility of the traffic signs. REFERENCES Armanto, R., Soelami, F.X.N. and Soegijanto, R.M. (2006) Evaluation on Luminaire Spacing Effect on Lighting Condition in Some Roadways in Bandung City. Bandung: Department of Engineering Physics ITB. Bama, H., Soegijanto, R.M. and Soelami, F.X.N. (2007) Evaluation on Lighting Condition in Concrete and Asphalt Surfaced Roadways in Bandung Case Study: BKR Street. Bandung: Department of Engineering Physics ITB. Bommel, W.J.M. and de Boer, J.B. (1980) Road Lighting. Deventer: Philips Technical Library. Cuvalci, O. and Ertas, B. (2000) Roadway Lighting Design Methodology and Evaluation. Journal of Integrated Design and Process Science, Vol. 4, No. 1, March Department of Transportation of Republic of Indonesia. (2007) Guideline for Traffic Facilities in National Roadways. Directorate-General of Land Transportation, No. AJ.409/1/1/DRJD/2007. Pradana, A., Soelami, F.X.N. and Soegijanto, R.M. (2007) Evaluation on Visual Legibility of Traffic Signs in Roadways at Nighttime. Bandung: Department of Engineering Physics ITB. Rea, M. S. (ed.) (2000) IESNA Lighting Handbook: Reference and Application, 9th Edition. New York: Illuminating Engineering Society of North America. Simons, R.H. and Bean, A.R. (2000) Lighting Engineering: Applied Calculation. Oxford: Architectural Press.