Pavement markings fit for ADAS

Against a backdrop of evolving minimum road marking standards, a new mobile retroreflectometer has emerged that allows a full road lane to be surveyed in a single pass

Words | Joe Turley, Reflective Measurement Systems Ltd, Ireland

Vehicle manufacturers and their advanced driver assistance systems (ADAS) suppliers are achieving rapid advances in automation, making their vehicles safer to operate on the public road network. Completely safe automated operation of vehicles will require significant assistance from road stakeholders through the adoption of worldwide uniform road markings and signs.

In this highly evolving and competitive market, information is slowly emerging from ADAS manufacturers in relation to what “good-quality” pavement markings look like. What is required of road markings in day/night, wet/dry and/or sunny conditions for ADAS to work effectively?

Up until now, it has been reasonable to assume that ADAS OEM manufacturers will not wait for road network stakeholders to get their roads ready for automated driving systems. The speed of ADAS innovation is just too fast. Systems such as machine vision and Lidar are being designed and developed with knowledge of the problems of current roads infrastructure.

Similarly, it is reasonable to assume that road stakeholders, road authorities and DOTs won’t invest until they have a clear definition of what grade road and pavement markings need to be to make their roads safe for both humans and ADAS. As more automation is incorporated into vehicles, and as these vehicles move from Level 1 to Level 3 and above, a more harmonized approach will be needed for the assessment and regulation of ADAS vehicle safety technologies.

Lack of uniformity

Exacerbating the problem is the lack of uniformity of pavement markings and signs across the world. This is changing, however. Based on emerging research supported by road/pavement trade bodies such as the European Road Federation (ERF) and American Traffic Safety Services Association (ATSSA), authorities are making moves at government level to harmonize road-marking quality and set minimum performance levels.

In October 2018, the Federal Highway Administration in the USA announced its intention to release a 2020 update of the Manual on Uniform Traffic Control Devices (MUTCD). This announcement coincided with the release of the US DOT’s latest policy statement on automated vehicle technologies: Preparing for the Future of Transportation – Automated Vehicles 3.0. This states that the MUTCD update, “will take into consideration these new [ADS] technologies introducing minimum pavement marking performance standards.”

The ATSSA has published recommendations that benefit human vision and ADAS (automation Level 1-2):

  • Minimum pavement marking retroreflectivity levels.
  • Longitudinal markings (edge lines, center lines, and lane lines) shall be six-inch wide on roads with a posted speed ≥ 40 mph (~65 km/h).
  • Lane line markings shall be 15 feet (~4.5m) in length with a gap of 25 feet (~7.6m).
  • Dotted edge line extensions shall be marked along exit and entrance ramps on roads with a posted speed ≥ 40 mph (~65 km/h). Crosshatch (Chevron) markings shall be included in gore areas on roads with a posted speed ≥ 40 mph (~65 km/h).
  • Non-reflective Botts Dots should be eliminated or only used to supplement pavement markings.
  • Contrast striping should be required on concrete roadways with a posted speed ≥ 40 mph (~65 km/h).

In Europe, the European Commission published its third Mobility Package, including a first set of technical recommendations that facilitate the recognition of road markings by human and vehicle vision systems. In February 2019, negotiations between the European Parliament and the European Council on a new Road Infrastructure Safety Directive achieved a milestone with the agreement that “high-quality road markings and road signs are crucial to support drivers and connected and automated vehicles”.

Once these new minimum and uniform pavement marking and sign regulations are in place over the next few years, road authorities and DOTs will have a legal and safety requirement to ensure their roads are compliant.

Measuring the visibility of road markings is essential for the safety of advance driver-assisted systems

Visibility and contrast

Until the advent of driving-assistance systems in cars, road markings and the standards that govern them were geared towards human drivers (Level 0). ADAS functions such as Level 1 features – lane departure warnings, for example – need to ‘see’ lane markings to determine if the vehicle has departed the lane. If the lane markings can’t be seen properly, the alert will not be triggered. For a vision system to image and recognize lane markings and other road safety features, there needs to be sufficient contrast to make the feature visible.

For instance, Toyota’s Lane Trace Assist technology depends greatly on the quality of longitudinal road markings, warning that “depending on the road conditions… the system may not work normally” and stating that the technology is “designed to read visible lane markers.”

Contrast, the difference in luminance or colour that makes an object – or its representation in an image or display – distinguishable. The higher the contrast value, the more distinguishable an object is and by extension the more visible. At night, lane markings that have very good retroreflectivity are visible because of their high contrast.

Good night-time contrast does not necessarily translate to the same during daylight hours. Achieving good lane marking contrast in a broad range of daylight conditions is critical to eventual rollout of automation Level 3 and beyond. Vision systems will play a central part in this rollout, a point of view put across forcibly by some vehicle manufacturers.

ADAS systems are sourced from multiple suppliers. While they may have similar functionality with similar performance, all will be programmed differently and with different machine vision algorithms. How are these systems baselined under different lighting conditions day or night? How is a measure of lane marking visibility scored? Coupled with the standardization efforts in the US and Europe and the existing marking standards (EN 1436 and ASTM E1710), validation of ADAS ability to use today’s roads requires a mobile, reliable, accurate and traceable lane marking inspection system.

A third-generation is here

RetroTek is the first in a new generation of mobile retroreflectometers that allows a full road lane to be surveyed in a single pass, in comparison with the industry’s previous generation of single-sided systems.

Using RetroTek, retroreflective measurements of left and right road lines, left and right road studs, median markers and central road markings are made in a single pass at normal road speeds by a single operator. The benefits of measuring the retroreflective performance of road marking material are many – good line visibility saves lives and significantly, as we move into the era of self-driving vehicles, ensures the road network is suitable for ADAS and autonomous vehicles.

RetroTek deploys technology that locates and inspects road markings using methods similar to those employed by ADAS in vehicles. Retrotek can help the pavement markings industry meet the challenges presented by ADAS with 100% lane coverage (from edge to center lines) in one pass – a 50% saving in travel distance and time with increased safety for the operator compared to traditional side-mounted, single- line retroreflectometers.

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