Sheetings used in disciplinary & informatory signs
Classification of retroreflective sheetings as per ASTM D4956 Standard
7year Engineer Grade Sheetings(EGS)
10year High Intensity Sheetings (HI)
Diamond Grade (DI)
Comparison of Engineer Grade & High Intensity Grade Sheetings
The main & most specific part of the sign is its retroreflective sheetings. Since some of the trips
are made during dark hours, signs must be lighted to be visible by the drivers.
External lighting is expensive & sometimes impossible. Our sheetings are as per ASTM D4956
Standard for which the minimum reflection values are given later in detail.
Retroreflective sheetings are a sheet of PVC in which glass beads (spherical) are placed in a
certain order. The light of the head lamps of the vehicle enter these beads which is reflected back to the
driver’s eye thereby enabling him to read & see the wording or message on the sign.
Retroreflective sheetings are classified as per the level of the reflected light. The value of the
reflected light is given by the manufacturer & also measurable by a reflectometer.
White colour has the highest value & brown the lowest value & black has no reflection at all.
As per ASTM D4956 standard, 9 classes of retroreflective sheetings exist (for more information,
refer to our website in English). Three of these have a more common consumption, namely:
1 – 7 year Engineer Grade (EGS)
2 – 10 year High Intensity Grade (HI)
3 – Diamond Grade (DI)
At present, sheeting’s manufactured by 3M, Avery,Kiwalite & Nikalite are as per ASTM & accepted by
the ministry of road & transportion.
These sheetings are widely used in disciplinary &
informatory signs. Minimum reflection value of white sheets are 70 candelas at start & maximum usable life is 7 years. In other words white sheetings have less them 35 candelas reflection when their usable life is finished & this statistically happens in year seven but it should be noted that in areas with high occurrence of sand storms this life decreases, sometimes up to a half. Most of the existing signs in Iran and other countries have used this type of sheetings.
These sheetings are used in route informatory signs. Minimum reflection value is 250 candela for start & minimum useful life is ten years. Most of route informatory signs & also signs used in arterial roads, use this type of sheeting in spite of their higher prices. Studies have proved that their longer life & efficiency causes signs to end up 30% cheaper in comparison with Engineer Grade material. In other words, for side & overhead signs in which the angle of observation from drivers eyes is large, this type of sheetings have a very desirable reflection. Therefore the use of this type of sheeting is of priority in route informatory signs.
This type of sheeting is used in route informatory signs & road works signs & in special circumstances. Its minimum reflection value at start is 800 candela with a minimum useful life of 10 years. Internal structure of this type of sheeting is different from the other two types & is composed of glass prisms. Due to potential hazards at roadwork sites (such as asphalt, drillings, excavations, bridge construction, etc.), this type of sheeting is used to warn the drivers. Base price of signs with this type of sheeting is around 3 times more then the Engineer Grade.These sheets have excellent reflections which are much higher than the other two types.
This Type of sheeting is made of a composition of prisms in the High Intensity Grade along with fluorescent paints. This paint absorbs the low wavelength ultraviolet radiation of the sun (which is invisible) & reflects them with high wavelength visible rays. This causes the sign to be more clearly visible in limited lights (such as cloudy weather & start & end of the day). This also makes the sign visible from longer distances & the drivers have more time to react to the sign message. These sheetings are High Intensity fluorescent with minimum useful life of 10 years & minimum reflection value as per ASTM D4956 is defined for yellow color. The acceptable types are 3, 4, 7 & 8.
The picture below belongs to 3M research division. The difference of 70 candela & 250 candela of the two types is clearly visible in the picture. After 7 years, the reflection value of Engineer Grade material decreases sharply but the reflection value of the High Intensity Grade after 10 years is even more than the reflection value of the Engineer Grade at start.
The conclusion is that using High Intensity Grade material is much better & more economical. It was mentioned earlier that these sheetings are composed of glass spheres. This is true for engineering & High Intensity Grade material but Diamond Gradeis composed of glass prisms.
One of the differences between the engineering & High Intensity Grade material is that in the High Intensity Grade, glass spheres are confined in a multi – sided holder which causes less damage to the focal length & the back mirror, thereby increasing the life time of these sheetings.
This is an instrument which measurers the reflection value of retrorflective sheetings & used to verify the correct condition of sheets.
The instrument has a diaphragm which is placed on the sheet surface & then the trigger button is pushed thereby emitting a light ray with an entrance angle of 0.2 degrees is sent to the surface & the reflection measured at – 4 degrees angle.This instrument is used for the following applications:
1- Inclusion of GPS. For road safety inspection, a GPS is very useful.
2- Accuracy of reflection measurement by one or a few buttons.
The models which measure all the colours by one button & have the intelligence to differentiate
between the colours, are simpler for use.
3- Memory space for recording the measurements.
4- Capability to be connected to a computer for data transmission.
5- Battery consumption & weight of the instrument.
•Monitoring the reflection of existing signs on the road to determine those which need replacement
(road safety inspection).
•Monitoring the reflection of sheetings after manufacturing which shows suitability of the reflection,
but for later years, other parameters must also be considered.