Traffic Signs Manual Chapter 4 Warning Signs
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- 1.5.1 ). 1.14.2.
| 1.14 Maintenance
1.14.1. Over a period of years, signs gradually become faded and their retroreflective properties diminish. This will reduce both conspicuity and legibility, by day and by night. Excessively discoloured or faded signs (e.g. white backgrounds which have become grey or brown, or red borders faded to pink) and signs where the legend or graphic is peeling cannot be fully effective and need to be replaced. Guidance can be found in TD 25, in Volume 8 of DMRB (see 1.5.1 ). 1.14.2. Signs should be cleaned at intervals appropriate to the site conditions. Signs located where they are subject to heavy soiling from passing traffic, or algae growth (a common problem for signs beneath tree canopies) will need more frequent cleaning. Neglect reduces the external contrast between the sign and its surroundings, making it less likely to be noticed by drivers. It also reduces the internal contrast between legend and sign background, making the sign more difficult to read. Moreover, it seriously reduces light transmission through the retroreflective medium. Dirty signs are far less effective at night. Older drivers are particularly disadvantaged; the ageing process of the eye means that progressively more light is required to maintain the same legibility performance. Dimmer signs take longer to recognise and to read, reducing the time available for drivers to take appropriate action. INTRODUCTION 13 1.14.3. The importance of maintaining the necessary clear visibility distance is emphasised in tải về 2.25 Mb. Chia sẻ với bạn bè của bạn:
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