Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2023.41.0058 Acta Polytechnica CTU Proceedings 41:58–65, 2023 © 2023 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague THE INFLUENCE OF MODERN HEADLAMPS ON THE RECOGNITION OF PORTABLE TRAFFIC SIGNS AND WARNING TRIANGLES Martin Rak∗, Tereza Tmejová, Tomáš Bilík, David Jelínek, Albert Bradáč Brno University of Technology, Institute of Forensic Engineering, Purkyňova 464/118, 612 00 Brno – Královo Pole, Czech Republic ∗ corresponding author: Martin.Rak@vut.cz Abstract. This article focuses on the issue of portable traffic signs and their visibility using different light sources such as halogen, Xenon, or LED. The measured values of luminance and retroreflection for each object are used to distinguish the individual results. The results show the differences between the various light sources on the visibility of the measured objects. Furthermore, from these results it is possible to evaluate portable traffic signs regarding degradation due to mechanical wear or aging. Keywords: Retroreflection, portable traffic signs, light sources, luminance, mechanical wear. 1. Introduction This paper expands on the authors’ previous publi- cation presented at the JuFoS conference and uses parts of the text from it [1]. Portable traffic signs have a significant impact on road safety in non-standard situations such as road repairs, detours, or traffic acci- dents. According to accident statistics, approximately 350 accidents in the Czech Republic are related to traf- fic signs every year. For this study, the term ‘portable traffic signs’ includes traffic devices and warning tri- angles since these are used in similar non-standard situations. One of the motives of this study was the existence of several variations of light sources in mod- ern vehicles such as halogen, Xenon, LED, or Laser diode, which are mentioned by [2–4]. The goal was to determine the visibility of portable traffic signs re- garding different light sources from different distances, considering factors such as proper placement of the sign or its degradation due to mechanical wear or aging. To achieve this, retroreflection and luminance measurements were carried out on selected samples of portable traffic signs, particularly 20 pairs of portable traffic signs and 5 different types of warning triangles. This project did not address the effects of adaptive technologies of modern headlamps, such as AFL or ADB, whose effects on visibility have been addressed by [5]. Based on the results and experience with the first static measurement, a second static measure- ment was carried out. The second static measurement compared halogen reflector headlamps and halogen projector headlamps. To reduce measurement inac- curacies, only new traffic signs and devices that are expected to meet the legislative requirements were used and new bulbs were fitted to both types of head- lamps. The measurement procedures and evaluation methodologies were identical to the first static mea- surement. 1.1. Current state There is a methodology for the placement of traffic signs in the Czech Republic set by technical stan- dards [6, 7]. Based on these standards, we recognize the following portable traffic signs and traffic devices. Portable traffic sign is vertical traffic sign placed on a red and white striped column and active surface of the sign must be retroreflective according to EN 12899-1. Traffic devices are mainly devices for traffic manage- ment. These include traffic cones, direction signs, or guide signs. Retroreflective materials should be used for sign faces according to EN 12899-1. The white stripes of traffic cones should be retroreflective accord- ing to EN 13422 [8, 9]. Retroreflection is a feature that allows the light cast by a vehicle’s headlights to be reflected back to the driver. This feature allows the driver to see the traffic sign in time and react to it during the day and in the dark [10]. There are three classes of retro-reflectivity – RA1, RA2, and RA3. The higher the class of the sheeting, the bet- ter the visibility of the sign or device at night. The methodology of measuring retroreflection, according to the mentioned standards, consists only the labora- tory measurement and does not consider the actual visibility by the driver in the real world. 2. Method 2.1. Methodology for measuring retroreflection Retroreflection values were measured on the entire set of portable traffic signs, traffic devices and warning tri- angles. For this purpose, signs and devices that were commonly used on roads were selected. The aim of the measurement was to verify whether the selected sings and devices meet the requirements of EN 12899-1 and EN 13422 in the case of traffic cones and ECE 27-04 58 https://doi.org/10.14311/APP.2023.41.0058 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 41/2023 The influence of modern headlamps Figure 1. Retroreflection measuring using Zehntner ZRS 6060 EN [1]. in case of the warning triangles [8, 9, 11]. A Zehnt- ner ZRS 6060.EN retroreflectometer was used for the measurements (see Figure 1 for example of measur- ing process). This is a device designed to measure the retroreflection coefficient RA of vertical traffic signs or other similar materials. This device is in- tended for measuring the retroreflection coefficient in the field. Before the actual measurement, it was necessary to clean each sign and to let the measuring device stabilize outside of the transport package for at least 5 minutes before the actual measurement. The measurement of vertical traffic signs (including traffic devices) is carried out at three randomly selected mea- suring points of the same-colored area. The device itself then averages these values and displays the re- sulting values of the retroreflection coefficient. These values can be compared with the values specified in the relevant standards EN 12899-1 and EN 13422. 2.2. Methodology for measuring luminance Luminance was measured using the LumiDISP. This device is luminance distribution analyzer that uses the analysis of luminance ratios with the help of digital photography to photometrically measure luminance and its distribution. The output of this device are luminance maps from which it is possible to determine the luminance value of individual traffic signs at any point in the captured digital image. Both portable traffic sign measurements were taken at a location where there was minimal light pollution. The first static measurement took place when the moon was new, and it was clear to partly cloudy. Three types of headlights were used for this measurement – halogen reflector, Bixenon and LED, all on Škoda vehicles. The second static measurement took place when the moon was nearly full, and the sky was clear. For this measurement, Škoda vehicles equipped with halogen reflector headlamps and halogen projector headlamps were used. The device was placed in front of the ve- hicle to avoid any disturbance of the windscreens of Figure 2. Placement of measuring device LumiDISP in front of the vehicle [1]. each vehicle, as shown in Figure 2. For each type of headlamp, measurements were collected for low beam and high beam settings. All the measurements were at an airstrip with a tarmac surface and a minimum gradient. The measured objects were each positioned 0.5m from the right side of the road and the center- line of the vehicle with the respective headlamps was 1.75m from the right side of the road. The first dis- tance measured was 80m, which is approximately the distance needed for the vehicle to stop from a speed of 9 kmh−1 including the driver’s reaction time of 1.0 s and applying the minimum required braking decelera- tion of 5.8m s−2 for passenger vehicles. The second distance was 350m, which was the maximum possible distance that could be achieved on the site. Averages of the luminance values of individual pixels for the marker area were used to evaluate and quantify the marker luminance. Therefore, comparisons can also be made between various traffic signs in different sizes. For the evaluation of the brightness of the triangles, a similar method as for the traffic signs was used. In the case of triangles, only the values of the physical parts of the triangles without background were used. The average luminance of each triangle included the internal non-reflective parts if the triangle had them. 2.3. Test measurements To determine the influence of the environment, tilt, or change of position of the measured sign, a test measurement was performed. The test measurement showed that the error of the measured values due to the influence of weather conditions was below 10%. A change of position (up to 10 cm) and a rotation of the sign (up to 5°) did not have any significant effect and were insignificant compared to the influence of the environment. 2.4. Headlamp adjustment and intensity measurement Prior to the second static measurement, both types of halogen headlamps were adjusted, including replace- 59 M. Rak, T. Tmejová, T. Bilík et al. Acta Polytechnica CTU Proceedings ment of halogen bulbs and adjustment. H4 and H7 halogen bulbs were used in the measurements for halo- gen reflector and projector headlamps respectively. The headlamps were then adjusted, and the illumi- nance measured. These operations were carried out using a Tecnolux 12799/LX2/P regloscope. This is a diagnostic device designed to check and adjust all types of headlamps. ’It is an optical-mechanical de- vice working on the principle of direct projection of the image of the light emitted by the headlamp and enabling the inspection and adjustment of headlamps of motor vehicles whose height above the ground is at least 200–1300mm [12]. 2.5. Traffic signs selection For the retroreflection measurements, both new signs and pairs of signs that were already in use were mea- sured. The measured values were compared with the respective norms to determine the state of degrada- tion of the signs. The measurements indicated that the retroreflection values can be used to determine to a certain extent the wear of the signs that cannot be determined otherwise (e.g., the absence of a manufac- turing label or details of eventual refurbishment). In the case of the second static measurement, only new traffic signs and devices were selected. 3. Results 3.1. The first static measurement For the first static measurement, similar Škoda vehi- cles equipped with different types of headlights were chosen. Specifically, the vehicles were a Škoda Octavia III (2018) with halogen reflector headlamps, a Škoda Superb III (2015) with Bixenon projector headlamps and a Škoda Superb III fl. (2022) with full LED Matrix headlamps. 3.1.1. Distance 80 m Low-beam mode Measurements with the LumiDISP device at 80m in low beam mode resulted in the highest values for Halogen headlights for all measured objects. For the remaining types of headlamps, the following patterns were apparent (see Figure 3): • Objects that were mostly below 150 cm height from the road surface displayed higher luminance values for full LED headlamps in comparison to Bixenon headlamps, • the remaining objects, which had the bottom edge at a height of 150 cm, displayed higher values for Bixenon headlamps in comparison to full LED head- lamps. High-beam mode At 80m in high beam mode, the highest luminance values were achieved when using the full LED head- lamps. In all cases, the Halogen headlamps performed better than the Bixenon headlamps. Curiously, for the warning triangles, Halogen headlamps came out better in high beam mode, although full LED head- lamps were better for the cones and other signs. The full LED headlamps performed the best with the signs with a border that used the RA3 sheeting, as expected. For the Halogen and Bixenon headlights, these signs showed similar values to the white signs using RA2 sheeting. Figure 4 provides a representation of the average luminance values measured for each portable traffic sign. Differences due to degradation can be seen for each pair. Figure 5 shows a series of LumiDISP outputs in the form of luminance maps demonstrating the differences between the headlamps for the same traffic sign. 3.1.2. Distance 350 m Low-beam mode For the measurements at 350m, five pairs of traffic signs were selected, which were similar in size and at the same time featured identical colors on different backgrounds, and one warning triangle. Again, in the low beam setting, the Halogen headlamps gave the best values for all measured objects, while the Bixenon headlamps performed the worst. The results for the warning triangle were in the same manner. High-beam mode For measurements at 350m in high beam setting, the full LED headlamps performed best, and the Bixenon headlamps again performed worst. As was the case at 80m, the Halogen headlamps performed best in the high beam setting. Figure 6 shows com- parison of different types of headlamps and beam modes. 3.2. The second static measurement For the second static measurement, two similar Škoda vehicles equipped with halogen headlamps were cho- sen. Specifically, the vehicles were a Škoda Fabia II (2004) with halogen reflector headlamps and a Škoda Roomster (2007) with halogen projector headlamps. Only new traffic signs were used for this measurement and new halogen bulbs were fitted in the vehicles to avoid any possible interference with the measure- ment. When measuring the illuminance, even when new bulbs were used, the projector headlamps of the Škoda Roomster were found to have a low intensity value, where the right headlamp did not meet the minimum intensity value required for vehicle opera- tion. In order to be able to compare the results, this fact was considered by recalculating the measured luminance ratios using the measured intensity values of the individual headlamps. For the second static measurement at 80m, the position of the sign above the road level was changed. According to TP 65 it is recommended to place the lower edge at a height of at least 60 cm above the road level [6]. In the case of this static measurement, the bottom edge of the sign was placed at a height of 105 cm and 150 cm on the post. The measurements also used traffic devices 60 vol. 41/2023 The influence of modern headlamps Figure 3. Luminance values (cdm−2) at 80m using a low beam headlamp setting [1]. Figure 4. Luminance values (cdm−2) at 80m using a high beam headlamp setting [1]. Figure 5. Comparison of traffic signs in terms of luminance, from left in order Halogen, full LED, Bixenon [1]. 61 M. Rak, T. Tmejová, T. Bilík et al. Acta Polytechnica CTU Proceedings Figure 6. Comparison of luminance values at 350m using a headlamp setting (Low-beam on the left, high-beam on the right) [1]. Figure 7. Comparison of luminance values at 80m using a Low-beam headlamp setting (height 150 cm on the left, height 105 cm on the right). whose design does not allow them to be placed at different heights. For this reason, they were placed at only one height as specified by the design. 3.2.1. Distance 80 m Low-beam mode Measurements with the LumiDISP at 80m in low- beam mode showed the highest values for the halogen reflector headlamps for all measured objects. After correcting the results in relation to the intensity of the headlamps used (“Projector +” in Figure 7), the halogen headlamps with projectors showed better re- sults in all cases. In the case of a lowering the height of the traffic sign from 150 cm to 105 cm, there was a slight increase in the brightness values for both the halogen reflector headlamps and halogen projector headlamps. As expected, for both headlamps, all the RA1 class signs came out worst. The signs with the larger white and red areas showed the best average luminance values. High-beam mode Measurements at the 80m distance in high-beam mode were also made for two different traffic sign heights. The results show that the halogen projector headlamp performed better for the signs placed with the lower edge at a height of 150 cm, even before recalculation to compare the light intensities. This is due to the alignment of the headlamps, where the main beam halogen projector was aligned higher than the main beam halogen reflector. Both headlamps were adjusted to the correct tolerance. For markers at 105 cm lower edge height, the halogen headlamp 62 vol. 41/2023 The influence of modern headlamps Figure 8. Comparison of luminance values at 350m using a different headlamp setting (Low-beam on the left, High-beam on the right). reflector came out better, and after conversion to the same luminous intensities, the halogen projector came out better, as it did for the low-beam mode headlamps. 3.2.2. Distance 350 m Low-beam mode The 350m measurement was conducted with the same traffic signs as the 80m measurement. The Lu- miDISP measurements at 350m in low-beam mode showed the highest values for the halogen reflector headlamp for all measured objects. Again, the results were corrected for the intensity of the headlamps used (“Projector +” in Figure 8). Again, in all cases the halogen projector headlamps showed better results. Also, at 350m, all traffic signs of class RA1 came out worst for both types of headlamps. The markers with the larger white and red areas showed the best average luminance values. High-beam mode From the lumi- nance measurements at 350m in high-beam mode, the halogen reflector headlamps again performed better. Compared to the halogen projector headlamps, the differences were not significant as with the low-beam headlamps. After correcting the results in relation to the intensity of the headlamps used, the halogen headlamps with projectors performed better in all cases. High-beam mode For measurements at 350m in high beam setting, the full LED headlamps performed best, and the Bixenon headlamps again performed worst. As was the case at 80m, the Halogen headlamps performed best in the high beam setting. Figure 6 shows com- parison of different types of headlamps and beam modes. 3.3. Warning triangles Within the individual static measurements, interesting observations were made concerning the warning trian- gles. After comparing the first and second measure- ments, it was found that there were some similarities between the measurements. Of the two measurements, the best results were obtained for the third warning triangle measured and the worst results for the fourth warning triangle. It can therefore be concluded that, in the case of warning triangles, it is not only the type of headlamps used to illuminate the warning triangles that matters but also, and above all, the construction and material properties of the particular triangles. Furthermore, it has been found that the reflective properties of individual warning triangles vary quite considerably, and these facts may have an impact on their possible use in real traffic (see Figure 9). Regarding the possibility of influencing the average luminance values of individual pixels, as mentioned in Section 1, also shown in Figure 10, which shows a series of LumiDISP outputs in the form of luminance maps demonstrating the different warning tringles for the halogen headlight with reflector. 4. Discussion The minimum luminance for recognizability of a traf- fic sign at night out in the rural area ranges from 35 to 340 cdm−2 according to [13]. According to AASHTO in the range of 20 to 180 cdm−2 [14]. Ac- cording to Elstad et al. [15] in the range of 35 to 70 cdm−2. According to Bullough et al. [16] ranging up to 280 cdm−2. According to Fletcher et al. [17] in the range of 20 cdm−2. According to Freyssinier et al. [18] in the range of 40 cdm−2. All types of headlamps in a high beam setting met these condi- tions at 80m. In a low beam setting, signs with RA1 63 M. Rak, T. Tmejová, T. Bilík et al. Acta Polytechnica CTU Proceedings Figure 9. Comparison of luminance values for warning tringles at 80m using a Low-beam headlamp setting (The first static measurement on the left, the second static measurement on the right). Figure 10. Comparison of luminance values for different warning triangles at 80m for halogen headlight with reflector using a Low-beam headlamp setting. background, predominantly amber or blue color, did not meet these values. 5. Conclusions In this study, average luminance values were measured for selected portable traffic signs as a whole or their sections (e.g., individual colors). These values were determined for the purpose of the first static measure- ment for different types of headlamps (halogen, full LED, Bixenon) in low beam and high beam modes at distances of 80 and 350m from the object to be mea- sured. The retroreflection values were compared with the values set by the standards and with the values measured by the LumiDISP device. By comparing the measured values from the two devices with each other, it was observed that in 2/3 of the cases the values showed similar patterns, which could be used to determine the loss of retroreflection for degraded signs. The second static measurement was designed to further understand the design characteristics of the halogen headlamps, and therefore measurements were made on the new portable traffic signs and using only new halogen bulbs, with the intention of eliminating measurement deviations. It was found that although halogen reflector headlamps showed higher measured luminance values, after correcting the results in re- lation to the intensity of the headlamps used, the halogen projector headlamps would perform better in all cases. In the light of the findings, the interpretation of the results of the first static measurement can be re- vised so that projector headlamps should show better brightness values than reflector headlamps. Thus, it can be concluded that the Bixenon headlamps used in the first static measurement must have had an overall lower illuminance which was not, however, related to the design characteristics. The aim of the measure- ments was to determine how the type of headlamp and the different design and material properties af- fect the visibility of the warning triangles. For the measurements, warning triangles already in use, as well as new triangles purchased for the purpose of the measurements, were used. After evaluating the results from both measurements, it was found that the visibility of the triangles is significantly influenced by their construction and material. In addition, the use of different types of headlamps also affects the results. 64 vol. 41/2023 The influence of modern headlamps All warning triangles met the minimum brightness limit for visibility set by [14]. Further measurements on a larger scale would be necessary to achieve more accurate results. These measurements served as a ba- sis for the implementation of measurements in regular traffic, where drivers’ reactions to portable road signs will be verified using eye-tracking. 6. Acknowledgements The authors would like to express appreciation for the support of: Transport Research Centre (CDV) (https://www.cdv.cz/), LumiDISP (https: //lumidisp.eu/), CTU in Prague Faculty of Trans- portation Sciences Department of Forensic Experts in Transportation (https://www.fd.cvut.cz/), and Michal Křižák, Brno University of Technology (https: //www.vut.cz/). This article was produced with the use of measurement equipment with the financial sup- port of the Ministry of Transport within the program of long-term conceptual development of research or- ganizations. This study was part of the project Qual- ity internal grants of BUT (KInG BUT); reg. num- ber: CZ.02.2.69/0.0/0.0/19_073/0016948. References [1] M. Rak, T. Tmejová, T. Bilík, D. Jelínek. Vliv moderních světlometů na viditelnost přenosného dopravní značení a výstražných trojúhelníků. In Sborník příspěvků konference Junior Forensic Science Brno 2022, pp. 47–51. 2022. [2] M. H. Rehan. Analysis of BMW and Audi headlights’ technology: International standards and road-safety in Pakistan, 2020. https://doi.org/10.13140/RG.2.2.28133.63208 [3] K. Sokanský. Světelná technika. České vysoké učení technické v Praze, 2011. [4] F. Vlk. Elektrická zařízení motorových vozidel. F. Vlk, 2005. [5] J. D. Bullough, N. P. Skinner, T. T. Plummer, et al. Adaptive driving beam headlights: visibility, glare and measurement considerations. Tech. rep., Rensselaer Polytechnic Institute. Lighting Research Center, 2016. [6] TP 65. Zásady pro dopravní značení na pozemních komunikacích, 2013. [7] TP 66. Zásady pro označování pracovních míst na pozemních komunikacích, 2015. [8] ČSN EN 12899-3. Stálé svislé dopravní značení – Část 3: Směrové sloupky a odrazky, 2008. [9] ČSN EN 13422. Svislé dopravní značení – Přenosná deformovatelná varovná zařízení – Kužely a válce, 2021. [10] PPK-FOL. Identifikace a možnosti použití retroreflexní folie pro svislé dopravní značky, dopravní zařízení a signalizační vozíky na dálnicích a silnicích ve správě Ředitelství silnic a dálnic, 2015. [11] ECE 27-04. Uniform provisions concerning the approval of advance-warning triangles, 2014. [12] Příloha č. 7 k vyhlášce č. 2011/2018 Sb. Vyhláška o technických prohlídkách vozidel. Základní charakteristiky přístrojů používaných k technickým prohlídkám vozidel, 2018. [13] T. M. Allen, F. Dyer, G. Smith, M. Janson. Luminance requirements for illuminated signs. Highway Research Record 179:16–37, 1967. [14] A. A. of State Highway, T. Officials. Roadway Lighting Design Guide. American Association of State Highway and Transportation Officials, 2005. [15] J. Elstad, J. Fitzpatrick, H. Woltman, et al. Requisite luminance characteristics for reflective signs. Highway Research Board Bulletin 336:51–60, 1962. [16] J. D. Bullough, N. P. Skinner. Luminance criteria and measurement considerations for light-emitting diode billboards. Tech. rep., 2011. [17] K. Fletcher, S. Sutherland, K. Nugent. Identification of text and symbols on a liquid crystal display part II: Contrast and luminance settings to optimise legibility. Tech. rep., 2009. [2022-09-25], https://apps.dtic.mil/sti/pdfs/ADA499459.pdf. [18] J. P. Freyssinier, N. Narendran, J. D. Bullough. Luminance requirements for lighted signage. In Sixth International Conference on Solid State Lighting, vol. 6337, pp. 357–364. SPIE, 2006. https://doi.org/10.1117/12.681422 65 https://www.cdv.cz/ https://lumidisp.eu/ https://lumidisp.eu/ https://www.fd.cvut.cz/ https://www.vut.cz/ https://www.vut.cz/ https://doi.org/10.13140/RG.2.2.28133.63208 https://apps.dtic.mil/sti/pdfs/ADA499459.pdf https://doi.org/10.1117/12.681422 Acta Polytechnica CTU Proceedings 41:58–65, 2023 1 Introduction 1.1 Current state 2 Method 2.1 Methodology for measuring retroreflection 2.2 Methodology for measuring luminance 2.3 Test measurements 2.4 Headlamp adjustment and intensity measurement 2.5 Traffic signs selection 3 Results 3.1 The first static measurement 3.1.1 Distance 80m 3.1.2 Distance 350m 3.2 The second static measurement 3.2.1 Distance 80m 3.2.2 Distance 350m 3.3 Warning triangles 4 Discussion 5 Conclusions 6 Acknowledgements References