At night-time the situation is something else: the performance of our eyes decreases to 5 % of the daytime performance. That is to say many objects relevant for navigation cannot be perceived in darkness. All the more good visibility of road markings is essential as these "simple lines on the floor" indicate the course of the road.
If we cannot see the white lines well, we start to feel insecure and focus our whole attention on them which would also be important for other things: dangerous situations could be detected too late. Good visibility of road furniture, mainly good visibility of road markings is therefore not a question of prestige or luxury; it is a crucial factor in ensuring traffic safety.
Good road markings are designed to reflect the light of a vehicle's headlamps in the driver's direction; this is called retro-reflection. It can be achieved for example by embedding small glass beads in the marking material.
Measuring principle RL
However, in a similar way as the road surface itself, the markings suffer considerable wear and tear through the constant overrunning by vehicles. Gradually, the glass beads will be detached and the retro-reflection meaning the night visibility will deteriorate more and more. Therefore, it is recommended to check the quality of road markings road-wide at regular time intervals.
This can be achieved by using a retroreflectometer: an optical measuring device which measures the night visibility of the road marking from the driver's perspective: The marking is illuminated with a light source similar to a vehicle's headlamps; an optical sensor stands in for the driver's eyes. A reproducible objective measuring value can be taken within seconds.
Handheld retroreflectometer ZRM 6013+
Minimum requirements for the performance of road markings are standardized in national and international standards and local regulations, making an objective assessment of the marking easy: with the help of the measuring value it can be decided whether the marking still meets the requirements and can be seen well by road users.
Even higher requirements apply for wet road surfaces: a regular marking is often not enough in these situations to guarantee good visibility. If a marking is to be seen in all weather conditions, the use of special markings with enhanced visibility in wet conditions is recommended.
This can be achieved by special profiles which aid the draining of water. The higher parts of the marking protrude over the waterline and are functional. Another solution can be the use of reflective beads with different optical properties to achieve good visibility both in dry and wet conditions.
The performance of the marking in wet conditions can be checked with the retroreflectometer, too: the road is sprinkled with water and the measurement can be taken after one minute. Comfortable innovative handheld retroreflectometers offer the possibility of timed measurement so the operator doesn't have to use a stopwatch for wet measurements.
Also other important properties of the marking and its surroundings can be measured with the new retroreflectometer models: the road levelling is important for the draining properties of the marking and an integrated camera can take on-the spot pictures of the marking from the perspective of the measuring geometry, delivering valuable information on glass bead distribution, soiling, abrasion and other factors.
Handheld retroreflectometer ZRM 6014 with wet timer and integrated camera
Long distance can be measured fast and reliably with mobile measuring systems, dynamic retroreflectometers. The vehicles travel in the traffic flow at speeds of up to 120 km/h without impeding traffic. Measuring values are recorded constantly and can be evaluated later easily on a PC or laptop on a digital map or on a spreadsheet complete with a photographic record.
This area-wide analysis method offers the advantage of a great overview of the marking condition and enables the systematic and intelligent application of maintenance management methods. The budget will only be used in areas where it is necessary and the quality of the marking – and with it also traffic safety - can be improved in the long run without spending more money.
A variety of retroreflectometers, from simple handhelds up to comfortable and far-reaching dynamic measuring systems suitable for every user's needs and budget are available from the Swiss manufacturer of precision instruments Zehntner GmbH Testing Instruments.
