Celebrating 50 years of transportation safety leadership and innovation, RoadVista has set the standard in retroreflectometer accuracy, reliability, and usability. RoadVista is committed to making roads visibly safer with a complete selection of instruments and laboratory testing services for roadways visibility. RoadVista offers accurate, easy, safe, and cost-effective testing solutions for traffic signs, pavement markings, sign sheeting and high visibility clothing both for humans and CAVs

RoadVista

What would you do if you were driving down the road and you could not see any of the lines? How would you stay in your lane? How would you know where to go? This situation is the reality on many roads in the United States and around the world. This is made even more challenging in inclement weather conditions. The problem is so prevalent, the American Society of Civil Engineers recently rated U.S. roads with a grade of “D+.”¹

The problem is compounded when autonomous vehicles (self-driving cars) are included. If the human drivers can’t see the lines, the computer-driving vehicles will not either. It is the general consensus in the AV industry (though lesser known to auto manufacturers and the general public) that improving road markings is a top obstacle to be overcome before Level 3 classification (conditionally automated AV) can be realized. At a failed demonstration of self-driving car technology at the 2015 Los Angeles Auto Show, Volvo’s North American CEO, Lex Kerssemakers, exclaimed, “It can't find the lane markings! You need to paint the bloody roads here!”

The Autonomous Vehicle industry and developers stand to be hit hard by delays caused by limitations of current road marking infrastructure. By the year 2030, AV’s are projected to comprise 25% of traffic and are expected to be an $87B industry². Delays caused by road marking infrastructure will heavily impact early investors and developers as the expected market growth is reduced and competitors are allowed more time to get in the game.

To most people, the stripes painted on the road are taken for granted. It's just a line painted on the ground. What's the big deal, right? In fact, there is quite a bit of engineering involved with applying the line to the pavement. Road stripes are critical safety features of the road with minimum standards recommended by local agencies, and the US Federal government very close to publishing minimum requirements³. Worldwide, it was estimated that in 2016, there were 1,366.2 kilo tons of coatings (paints, thermoplastics, preformed tapes, epoxies, etc) applied to the roads to help ensure good visibility4. This shows that the industry is very large and vital to ensuring safety of motorists.

In addition to the different types of paints and thermoplastics used to create highly durable lines that can withstand the rigors of traffic driving over the top of them, night-time visibility is enhanced by embedding small glass spheres in the paint or thermoplastic material used to create markings. These beads act as retroreflectors, returning light from a car’s headlamps to the driver’s eyes. However, there are several process variables, including sphere diameter, sphere placement density, and the depth to which the beads are embedded, which affect the precise level of marking retroreflectivity, and therefore visibility, at night. As you might imagine, because of the minimum visibility requirements and ongoing safety research, there are tools that can help ensure road lines are clearly visible to both human and computer drivers.

Gamma Scientific’s RoadVista division has been at the forefront of road stripe measurements for more than 40 years, having developed the first commercially available pavement marking retroreflectometer for 3M Company in the 1970’s. Now, RoadVista products are used extensively all over the world for managing road signs, road stripes, and reflective pavement markers. More recently, RoadVista has developed laser-based technology which can perform highly accurate visibility measurements of pavement markings while driving down the road with the speed of traffic and evaluating the performance of every line on the road. The system, called the Laserlux G7 (LLG7), incorporates one, two, or three diode lasers, with output at red, green, blue, and infrared wavelengths. Within the instrument, the laser beams are projected onto an oscillating mirror to create a horizontal laser line that projects out onto the road surface. The scan lines are projected out on to the roadway and the return signal is measured. Real-time analysis of the data gives the line’s visibility, both in terms of brightness of the line and contrast with the pavement, along with the line’s perceived width, color, and location. This allows the operator to quickly evaluate the performance of the lines, and locate problem areas that should be re-striped, both for human drivers and autonomous vehicle sensors.

The key to making the system user-friendly was to make it easily deployed. To help with that, the engineers at RoadVista turned to Hollywood. External vehicle mounted cameras are commonplace in movies and TV where car chase scenes are prevalent. RoadVista saw that those mounting systems could easily be modified to accept mounting the LLG7. The mounting system utilizes high-strength vacuum cups that stick to any smooth vehicle surface and holds 20 times the weight of the LLG7, ensuring the system is completely secured to the vehicle. The LLG7 is powered by a 12VDC accessory outlet in the vehicle and is operated wirelessly via any tablet, smartphone, or laptop computer.

The ease of use and data quality of the LLG7 goes a long way towards enabling wide scale measurement of the visibility and performance of pavement markings. Really all the operator does is attach it to the car, turn it on, and then drive around. The system automatically acquires the data, along with GPS coordinates, and stores this on a flash drive. Plus, the use of red, green, and blue lasers enables marking color measurement to ensure white is white and yellow is yellow. Alternatively, the utilization of an infrared laser enables measurements of the road the way many self-driving cars will see it.

So, the next time you're driving down the road, take a look at those lines you're following. It’s more than just a strip of paint on the ground. Countless hours have been put in researching and formulating that stripe. RoadVista has played a key part in making sure that line is visible for not just you, but for the self-driving car that will be sharing the road with you very soon.

Eric Nelson | RoadVista Product Line Manager

1. “Infrastructure Report Card,” American Society of Civil Engineers, https://www.infrastructurereportcard.org/ (2017).

2. “Self-driving Cars an $87 Billion Opportunity in 2030, Though None Reach Full Autonomy,” Lux Research, http://www.luxresearchinc.com/news-and-events/press-releases/read/self-driving-cars-87-billion-opportunity-2030-though-none-reach (May 20, 2014).

3. “Summary of the MUTCD Pavement Marking Retroreflectivity Standard,” Federal Highway Administration, Publication No. FHWA-SA-10-015, https://safety.fhwa.dot.gov/roadway_dept/night_visib/fhwasa10015/ (April 2010).

4. “Traffic Road Marking Coatings Market Analysis By Product (Paint, Thermoplastic, Preformed Polymer Tape, Epoxy), Growth Prospects, Value Chain Analysis, And Segment Forecasts, 2014 – 2025,” Grand View Research, http://www.grandviewresearch.com/industry-analysis/traffic-road-marking-coatings-market (June 2017).

What is a handheld retroreflectometer?

For pavement markings, the retroreflectometer is an instrument that mimics the driver geometry with a light source acting as the vehicle headlight and a detector photopically corrected to match how human eyes perceive light acting as the human eye. The international standard geometry of the instrument is the CEN 30 Meter Geometry, to which all required retroreflectivity values are referenced. The CEN 30 Meter Geometry uses what is called a “standard vehicle” with typical height for the headlights above the ground and typical height of the driver’s eyes above the ground with the driver looking 30 meters (~100 feet) in front of the vehicle.

This retroreflectometer is placed on top of the pavement marking and a measurement is taken following the manufacturer’s instructions for instrument operation. The typical measurement area of a retroreflectometer is a rectangle approximately 2 to 2.5 inches wide and about 8 inches long.

Practical Use

As stated above, the retroreflectometer is taking a measurement of a very small area of the pavement marking. This single measurement may or may not be indicative of how the pavement marking is performing overall. Drivers are not looking at small 8 inch long sections of the pavement marking 30 meters in front of the vehicle. Drivers are looking at the line continuously and getting an overall view of how the pavement marking is performing. Pavement markings themselves inherently have a lot of variability, with 20% differences in retroreflectivity of flat markings being quite common just a few inches away from each other. This is before adding additional uncertainty of measurements being made in the field when roads are not flat and there can be rocks and other debris that can make positioning the retroreflectometer on the marking a bit more difficult. What’s important to remember is you want the retroreflectometer to feel solidly placed on the ground. You do not want the retroreflectometer to be level, you want it to be flat on the ground. Being flat on the ground will ensure the most accurately aligned position for the measurement.

Retroreflectometer Uncertainty and Reproducibility

ASTM has published Precision data for handheld pavement marking measurements in their standard document E1710 titled Standard Test Method for Measurement of Retroreflective Pavement Marking Materials with CEN-Prescribed Geometry Using a Portable Retroreflectometer (https://www.astm.org/e1710-18.html). The data is shown in Table 1 of the Standard. Reproducibility on a single measurement using a handheld retroreflectometer can vary between 11% and 28%. This means you can expect up to a 28% difference between measurements made two different retroreflectometers. If you limit your data collection to a single retroreflectometer, the Repeatability of a single measurement varies between 3% and 9%. That’s better, but it can still be improved upon. But how?

Handheld Retroreflectometer Data Collection Procedures

The way to improve the uncertainty of the measurements is to average together multiple measurements. Think of it this way: if you roll a pair of dice, on average, you will roll a 7. For any one given roll, you’ll get a number between 2 and 12. You could roll a 7, but you could also roll a 12 or roll a 2. That’s a big range of numbers. But the more you roll the dice, the closer and closer the average value will come to 7. So, if you want to ensure the average value of your rolls is 7, keep rolling. The same thing applies to pavement marking retroreflectivity measurements. The more measurements you take, the closer your average value will be to the performance value of the line. If you spread out your measurements over a distance, you also have the added benefit of seeing how well that line performs along its entire length.

But how do you know how many measurements you need to take? Luckily, the smart folks at ASTM have figured this out for you and published a procedure titled Standard Practice for Evaluating Retroreflective Pavement Markings Using Portable Hand-Operated Instruments. It is standard number D7585/D7585M. (https://www.astm.org/d7585_d7585m-10r22.html).

The Standard indicates that for sections of roads less than 3km long, a 125m section of roadway should be identified and it is recommended that 16 measurements be made over the 125m section and averaged together as a single value. For road sections from 3km to 1 km long, at least three separate 125m sections should be measured, and for road sections longer than 16km, more than three separate 125m sections should be measured, as determined by the agency with jurisdiction. This works out to be 1 measurement every 6m on continuous lines. For skip lines, you want to measure each skip at 2 different locations over 20 skip lines. If you are measuring structured or profile markings, you may need to average together multiple measurements at the same location, moving the instrument forward by a few inches, depending on the periodicity of the profile. That group of measurements would be considered a single measurement following the D7585/D7585M procedure.

At this point, you’re probably thinking you’re not excited about having to make so many handheld measurements. The good news is you don’t always have to. For example, let’s say you’re testing to make sure your retroreflectivity values are above 100 mcd/m²/lux. If your first 3 or 4 measurements are all in the 500-600 mcd/m²/lux range, then just stop right there. Your average value will have a higher uncertainty if it’s an average of only 3 or 4 measurements, but since they are all significantly higher than the minimum value, even with the higher uncertainty you can deem that section of road to be meeting the minimum requirements. But if your first few measures values are in the 100-150 mcd/m²/lux range, then you should perform all 16 measurements in that section.

In Summary

Start with a high quality, well maintained, calibrated retroreflectometer.

When performing a measurement, position your retroreflectometer so it is solidly placed on the pavement marking. Don’t use bubble levels or any other leveling tools. You want the instrument to be flat against the ground, not level with the earth. Use tools that will ensure your instrument is flat against the ground.

Do not rely on a single measurement to determine the performance of a pavement marking. Drivers are not looking at a small spot on the line, so you need to take a number of measurements down the length of the marking. Additionally, profiled markings may require multiple measurements in the same location to achieve a good result.

Plan on doing 16 measurements over a 400 foot (120m) section of road for every 2 miles of roadway you need to measure. If your markings are in good shape and measuring well above the minimum required value, you can reduce the number of measurements you need to take based on the statistical analysis shown in ASTM D7585/D7585M.

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The Laserlux G7 Mobile Retroreflectometer quickly and securely mounts to almost any vehicle with the Squid Mount™ vacuum mount system providing easy adaptability into existing resources without significant extra costs, both stand-alone as a single device, or in tandem with two instruments mounted to either side of the vehicle for full lane measurements. Assessment of retroreflectivity in both the visible and infrared spectrum create safer roads for both human and machine vision for autonomous vehicles.

Laserlux G7 Mobile Retroreflector

Portable vehicle mounted retroreflectometer

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