Proceedings of the Institution of Civil Engineers Transport 157 November 2004 Issue TR4 Pages 252–254 Paper 2312795 Paper published Proc. Instn Civ. Engrs Transport, 2003, 156, Feb., 17–28 Discussion: Segmentation algorithms for road marking digital image analysis M. P. N. Burrow, H. T. Evdorides and M. S. Snaith S. Xavier, Highways Agency, Traffic Signs Team, Dorking Office, UK 1. Congratulations to the authors! This is a very useful exercise as it uses the mathematical technique of algorithms to study the body of road markings against the contrast of bituminous road surface. It is able to identify to what extent the material present is worn out. This is very useful for high speed inspection purposes as a walk about inspection with the involvement of traffic management is not only resource intensive but also disrupts traffic flow and causes delay to road users. 2. Practising civil engineers approach this aspect of the inspection of road markings in a different way as set out in BS 3262 which is now superseded by BS EN 1824. 1,2 The former used a wire grid to place over the road marking. In that method a panel of inspectors formed a view of how much of the road marking remained within each grid square in a formal road trial and summed it over the test area and applied a simple calculation to determine the wear index. In the BS EN 1824 there is a ‘faster’ method that permits a coloured photograph to be taken on site and analysed back in the office. Instead of this somewhat cumbersome operation, an alternative permitted in the BS EN 1824 is to measure the property known as minimum luminance coefficient in diffuse illumination ( Q d ) using a portable instrument. This does not, however, tell us anything about how much of the line is worn out but nevertheless measures reflection under daylight or street lighting. This helps to form a view about threshold values for pre-view time of the road users. Incidentally, there is a useful European report and software for this which unfortunately does not take into consideration the presence of road studs. 3 I believe the BS ENs are reliable as there are years of tried and tested engineering methods behind them but they are costly and disruptive to traffic as the authors themselves have found. 3. In this context, the authors proposal is very attractive if photographic or video images can be taken from a high speed monitor and they are speedily analysed for useful results for decision making to replace a badly eroded line. Some pioneering work in this area was carried out at TRL between 1992 and 1995. Both Mr B. W. Ferne and I refer to it in our earlier discussion contribution. 4 Moving on from there, there are two monitors used by industry for a different measurement at high speed. They are known as the Ecodyn and Laserlux. Both measure the property of retroreflection (R L ) which is important for visibility at night. The latter system also has an option to take video images and a GPS facility. 4. Having taken snap shots at high speed, which may be considered as equivalent to taking walk about inspection photographs to BS EN 1824, the next step is analyse them in minute form for engineering decision making processes. 5. The authors have taken the trouble to study seven photographs. Simple visual inspection is described but I wonder what would be the corresponding assessment using the BS 3262 grid method and BS EN 1824 method albeit the photographs may be in black and white. It may be Q d measurements were not taken on site at that time or samples may not have been taken for closer examination in the laboratory. 6. The Highways Agency maintenance standard TD 26 pre- publication draft 5 gives guidance on measurement on wear index or Q d by inspectors under traffic management conditions permitting. The use of high speed monitors for the measurement of R L is also permitted subject to correlation with static measurement instruments. 7. Perhaps the authors could comment on whether the algorithmic methodology could be easily devised to form a view of how much of the road markings were remaining per square metre in each of the seven photographs and if so what the results are and how they compare with BS 3262 and BS EN 1824 methods. Do they have a view on how long they need to develop their methodology before road making industry partners who are already operating Edcodyn 6 and Laserlux 7 may begin to consider them as useful bolt-on devices to their systems? REFERENCES 1. BS EN 3262-2: Hot-applied thermoplastic road marking materials – Specification for road performance. British Standards Institution, London, 1999. 2. BS EN 1824: Road marking materials – Road trials. British Standards Institution, London, 1999. 3. European Commission 1999, Directorate General Transport, Co-operation in the Field of Scientific and Technical Research, COST 331 – Requirements for Horizontal Road Markings – Final Report of the Action. Transport 157 Issue TR4 252 Discussion Downloaded by [] on [22/05/20]. Copyright © ICE Publishing, all rights reserved.