road marking scanned by dual line retroreflectometer RetroTek-M

Future-proofing road markings

With the advent of autonomous and semi-autonomous vehicles, efficiently surveying and maintaining the quality of road markings has never been more important when it comes to safety.

Autonomous and semi-autonomous vehicles are now being driven and tested on our roads. Improving road safety is a key factor in these developments. Today’s production cars already have automated navigation, lane-keeping and parking functions. These vehicles rely on a suite of sensors to provide real-time feedback of road conditions, allowing onboard computers to make safe decisions. One such sensor will be a multicamera vision system looking at road markings, lines and road signs. It is not possible to crowd source retroreflectivity measurements, as the lights and cameras in current vehicles are not calibrated and do not have an accurate CEN 30 geometry.

Why are road markings necessary?

The essential purpose of road markings is to guide and control traffic, supplementing the function of traffic signs. Markings also serve to signify the segregation of traffic lanes and clearance from hazards. In an autonomous vehicle future, road markings will augment lane detection and will also continue to provide the vehicle (and its user) with a clear lane delineation.

What quality of road markings in day and night conditions will autonomous vehicles require to operate efficiently and safely for all road users? That is the burning question that global road authorities and road maintenance companies are asking manufacturers of autonomous cars. Many cars today have lane departure warning systems that use the line markings, for example, Tesla Motors incorporates lane line detection in its cars fitted with an autopilot system and many other car manufacturers are following its example.

Fading lines

All these autonomous vehicle systems assume that line markings exist, are clear and, more importantly, are visibly distinct. However, the US Department of Transportation estimates that 65% of its roads are in poor condition, meaning that autonomous vehicles will have considerable difficulty driving on them.

Industry executives say that inadequate infrastructure has become a roadblock to the development of self-driving cars, vexing engineers and adding time and cost to installations. Poor markings and uneven signage on the three million miles of paved roads in the USA are forcing automakers to develop more sophisticated sensors and maps to compensate. According to the European Transport Safety Council, EU rules on road infrastructure safety should also be revised to meet the needs of such vehicles, for example to mandate clear markings on all roadways.

Road authorities strive continuously to maintain safe and efficient road networks, but struggle with limited funding. Consistent quality control with regular monitoring ensures that funding helps improve road safety and will not be not wasted on under-performing maintenance work.

What are ‘visibly distinct’ markings?

Vehicle manufacturers may consider that existing road-marking, reflective pavement markings (RPMs) / road studs and sign standards are all that is needed for autonomous vehicles to perform safely and efficiently, provided the minimum standards are enforced. The standards CEN EN1436 and ASTM E 1710 were created to assess the night-time visibility of road markings. Road markings that adhere to these standards are visibly distinct in daytime and night-time driving. Certified retroreflectometers are necessary to check the retroreflectivity of road markings.

Markings, like everything on a road surface, are subject to wear and tear caused by traffic and environmental conditions. The constantly changing condition means it is often difficult and time-consuming to monitor their quality. To maintain accurate maps of road-marking quality will require road authorities and road maintenance companies to perform regular periodic surveys, perhaps several times a year. When autonomous vehicle manufacturers finally decide upon the quality and visibility of road markings necessary for safe passage, these road-marking maps will have to be maintained (this will probably be mandated by the regulating authority).

Road authorities and road maintenance companies will require systems to continually access and monitor the retroreflectivity of road markings, to ensure they are safe, economically and environmentally friendly and legible at all traffic speeds, causing no interference to traffic flows.

RetroTek-M hardware can be mounted on almost any vehicle

Introducing the RetroTek-M

Unlike existing dynamic single-line side-mounted retroreflectometers, the RetroTek-M from Reflective Measurement Systems (RMS) has the capability to survey simultaneously six streams of road asset data in a single pass, i.e. the retroreflectivity of longitudinal road markings, transverse markings, object markings and special markings in the center of the lane, as well as the presence or absence of reflective pavement markings (RPMs)/road studs and barrier reflectors. Furthermore, because both sides of a lane and full lane width are inspected simultaneously, travel and survey times are reduced by 50% or more.

The RetroTek-M retroreflectometer is attached to the front of a testing vehicle. It contains cameras that can image the full lane width, which is illuminated by a projected light source in a geometry that conforms to EN 1436, ASTM E1710 and EN 1463.

Sophisticated machine vision software is used to locate road markings, reflective pavement markings (RPMs) / road studs and barrier reflectors in the field of view. This data is then combined with GPS to accurately locate each measurement made. Precision driving in close proximity to road markings is not required. The repeatability and reproducibility of RetroTek-M inspection results forms a key pillar of RMS’s research and development process.

Road assets identified: 1 & 2 = lines/ markings; 3 & 4 = reflective pavement markings (RPMs) / road studs; 5 = barrier reflectors; 6 = center road markings/symbols

Certified accuracy

In July 2015, certification company StrAus-Zert confirmed the RetroTek-M as a suitable mobile pavement retroreflectometer for measuring the coefficient of retroreflected luminance of road markings. The RetroTek-M is the first ‘dual-line’ dynamic traffic-speed vehicle-transferable retroreflectometer system to be certified to CEN EN1436.

With its ability to simultaneously measure the lines on both sides of a lane to CEN EN1436, including road studs, the RetroTek-M is the most efficient and versatile mobile retroreflectometer system on the market.

Dr Hans-Hubert Meseberg of StrAus-Zert noted in his assessment report that the RetroTek-M showed nearly identical readings to the handheld LTL-XL. Meseberg also observed that the performance of the RetroTek-M was not affected by the velocity at which the measurements were taken.

Real-world application

In March 2016, using the RetroTek-M technology and in collaboration with RMS, Northern Road Markings (NRM) secured a contract from Transport Infrastructure Ireland to survey over 12 weeks the retroreflectivity of the primary and secondary road infrastructure (some 5,000km long, made up of motorways, dual carriageways and single-lane roads; 1,187km of it motorway).

“The flexibility of the RetroTek-M has allowed Northern Road Markings to meet and exceed the stringent requirements set by Transport Infrastructure Ireland,” says Mark Kelly, CEO of NRM. “Its ease of setup, its ability to measure line retroreflectivity, barrier reflectors and reflective pavement markings (RPMs) / road studs on both sides of a lane, as well as providing a platform to capture junction condition, makes the RetroTek-M a competitive choice.”

This article was written by Joe Turley and published in the Intertraffic World Annual Showcase 2017

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