Retroreflective materials are designed to reflect light back towards its source with minimal scattering. A retroreflectometer is a device used to measure exactly how much light is being returned to the source, or in other words, how reflective a material is. Local authorities and/or road maintenance contractors can use retroreflectometers to ensure that road signs meet the minimum reflectivity standards, thus ensuring they are performing as required and keeping drivers safe at night.

In this blog we look at the why, how and when for measuring the retroreflectivity of road signs, as well as some considerations that should be made ahead of purchasing a retroreflectometer.

What do reflection and retroreflection have to do with safe driving conditions?

First of all, let’s cover off the whole reflection vs retroreflection bit. Oftentimes people use the word reflective, when they actually mean retroreflective. If you’re interested in the technical difference between the two, see our blog What is a Retroreflective Material & How Does it Contribute to Road Safety? but, for the purposes of this blog (and the nice people at Google – Hiya!), let’s stick with the more commonly used term, reflective.

So, back to the link between the reflectivity of road signs and road safety. Although only about 25% of road journeys take place at night, the US Federal Highways Administration suggests that about 55% of fatal accidents also occur at night. They also report that inadequate and poorly maintained road signs and markings are often cited as the contributing factor to these night time accidents.

Safe traffic conditions depend on adequately performing traffic signs and road markings. At night on dark roads, the reflection created by traffic signs is essential to communicate important safety rules and messages to both drivers and pedestrians, maintaining order and reducing accidents.

During wet and rainy weather, even high-performing traffic signs present a challenge, as water droplets scatter the light, reducing the efficiency on the reflectivity. For more on this, see our blog The Ultimate Guide to Dew-Resistant Overlay Film >.

In short, reflectivity of road signs is a crucial parameter in keeping people safe on the roads at night.

How to measure the reflectivity of road signs

A retroreflectometer is the only way to objectively (and accurately) determine whether a road sign provides the minimum standard of reflection required.

After extensive testing we selected the RetroSign GRX from Delta as our preferred device as it is one of the most advanced retroreflectometers available on the market. It is built in accordance with existing standards to allow for retroreflection measurement of various colours and all types of reflective materials, including fluorescents. It has a rugged design and is built for long-lasting field work, as well as laboratory use. Perhaps most importantly of all, it’s also versatile and very easy to use.

As the UK distributor for the RetroSign GRX you can find more detailed information on the options available here, and if you’re interested in purchasing a RetroSign GRX, please get in touch with our friendly team today.

Preparations before arriving at site

1. Identify the road signs whose values are to be measured.
2. Consider the environment, will an extension pole and/or a ladder be required?
3. Pack appropriate health and safety PPE for those attending site.
4. Charge the GRX.
5. Bring cloths, water, and a mild detergent in case the road signs need to be cleaned ahead of measurement.

Preparations at a location

1. Decide if it is safe to get to the road sign even when using an extension pole and/or a ladder.
2. Clean the road sign (if required) and allow time for it to dry.
3. Note the type of road sign and the colours of the background and the legends.
4. Turn the GRX on, check the calibration and recalibrate, if necessary.
5. Check that the GNSS signal is received (if used).
6. If the extension pole is needed, mount the GRX on the extension pole and prepare the remote display.

Taking the measurements

1. Measure the values of each retroreflective colour of the sign at a small number of locations while positioning the GRX vertically and ensuring full contact.
2. Check if the values of each of the retroreflective colours are realistic and reasonably uniform and repeat measurements if necessary.

The results

Once the measurements are taken, the results are immediately displayed on the 5-inch WVGA colour touch display, clearly visible even in bright sunshine. In addition to the numerical readings captured, the GRX also displays a green thumbs up for signs which have met the required level of retroreflection, or a red thumbs down for signs which have not.

In addition to the on-screen readings, the data collected by the GRX can be transferred to PC via USB memory stick or transferred to another media via WiFi. The data can then be viewed in generally available software like Excel or displayed on Google Earth. The built-in digital camera also makes it possible to take photos of signs, which can also be attached to the data presentation in Google Earth as shown below.

How often should the reflectivity of road signs be measured?

National Highways CS 125 inspection of traffic signs is a UK standard which sets out the requirements for the inspection of all permanent traffic signs. Our blog A guide to ‘National Highways CS 125 Inspection of Traffic Signs provides lots of information about the requirements but in short…

All permanent traffic signs must be visually inspected every two years. If the individual suspects that the reflective properties of the sign are underperforming, then the reflectivity of the sign should be measured using a retroreflectometer.

In addition to the above, the reflectivity of all RA1 class road signs should be measured seven years after installation, and the reflectivity of all RA2, R2, R3B-UK & R3C-UK class road signs should be measured ten years after installation.

Learn more about the reflective material classes with our blog What is Class R3C? An Overview of Class R3C Traffic Sign Materials >

Other considerations when purchasing a retroreflectometer

Will your needs change over time?

If you’re going to invest in a high-tech piece of kit such as a retroreflectometer, it’s probably wise to go for something that offers flexibility and some degree of futureproofing.

The RetroSign GRX comes with all features preloaded, but just those paid for are made available. If a new requirement arises, the user can upgrade the device there are then by scanning a QR code with the GRX’s built-in camera.

Will you need to take measurements for different observation angles?

The most common observation angle (0.2°) shows the retroreflection as observed by the driver in a passenger car. However, it may also be necessary to test the retroreflectivity of road signs at additional observation angles, such as the retroreflection as seen by a driver in larger vehicles like SUVs, lorries and buses.

The RetroSign GRX is therefore offered in three base models where the figure indicates the number of observation angles the device is capable of measuring.

1. GRX-1 (1 entrance and 1 main observation angle)
2. GRX-3 (1 entrance and 3 observation angles)
3. GRX-7 (1 entrance and 7 observation angles)

Choosing the right retroreflectometer with Lakeside Group

If you would like to know more about the RetroSign GRX and whether it’s the right bit of kit for your project, please get in touch with us today. Our in-house technical support can talk through your requirements and make recommendations over the phone, as well as provide in person training for any individuals who will need to use the equipment in the field.