Everything State and Local DOTs need to know to comply with Mandatory Minimum Retroreflectivity Standards for Pavement Markings on US public roads.
This final rule applies to State and local DOTs in the execution of their highway programs, specifically with respect to the retroreflectivity of pavement markings. In addition, pavement marking improvement is elligible for up to 100 percent Federal-aid funding. This also applies to local jurisdictions and Tribal governments, pursuant to 23 U.S.C. 120(c).
The Federal Highway Administration’s decision to set standards on the minimum levels of retroreflectivity for pavement markings to all roads open to public travel in the United States has given road authorities 4 years to comply with the new standard. In this article we answer the frequently asked questions that Departments of Transport may have about compliance with the new standard.
Why has this new standard been introduced?
This latest update to the Manual on Uniform Traffic Control Devices (MUTCD) has been introduced to reduce fatalities and serious injuries on the US road network. The quality of pavement markings has been proven to have a significant impact in reducing road accidents and particularly in low light conditions and nighttime driving. Minimum standards for retroreflectivity of longitudinal pavement markings will ensure that road users will have clearer delineation on the road to provide safer journeys. The ruling will also help to support the operation of Autonomous Driver Assisted Systems (ADAS), such as Lane Departure Warning and Lane Keep Assist that are increasingly dependent on high quality pavement markings to operate correctly.
What are the new standards for retroreflectivity?
- The minimum retroreflectivity of longitudinal pavement markings is 50 mcd/m2/lux on roads with speed limits of 35 mph or greater, where average annual daily traffic is 6,000 vehicles per day.
- The minimum retroreflectivity of longitudinal pavement markings is 100 mcd/m2/lux on roads with speed limits of 70 mph or greater.
The FHWA has decided that this standard does not apply to other pavement markings such as center symbols, arrows, chevrons or words and that crosshatch markings, transverse markings and crosswalks are excluded from the minimum standard.
What is retroreflectivity?
Retroreflectivity is a measure of the ability of a surface to return light to its source. Retroreflectivity enhances the visibility of pavement markings and center road markings, warnings and symbols in low-light and night-time conditions. A driver’s awareness of lanes and road edges is improved when the vehicle lights are reflected off the pavement markings.
How is retroreflectivity achieved in pavement markings?
Road Striping contractors apply a distribution of glass beads when applying the pavement marking material. It is the glass beads sitting on the surface of the pavement marking that provides the reflective surface for light that hits it from vehicle headlights. As a result, it is critically important that glass beads are applied correctly during the pavement marking process. If they sit too high on the pavement marking material they are likely to be knocked off by tire friction. If they are buried too deep in the pavement marking material they will not provide any reflectivity at all.
Why would retroreflectivity levels change on pavement markings?
The effectiveness of retroreflective materials tends to deteriorate over time, so regular checking and maintenance of pavement markings is important. Pavement markings degrade as a result of corrosion caused by exhaust fumes, industrial pollution, friction from vehicle tyres, sun exposure, dirt, rain, ice and wind. Regular inspection and measurement ensure that minimum acceptable standards are maintained.
How are retroreflectivity levels measured?
Retroreflectivity of pavement markings can be accurately measured with a retroreflectometer. These measuring systems are designed to shine a light on the pavement marking, effectively mimicking the behavior of vehicle headlights and measuring the light reflected back from the surface of the pavement marking to the driver.
There are three types of retroreflectometers available –
- Handheld retroreflectometers enable spot measurements to be taken manually, but these obviously require traffic management and lane closures to ensure the safety of survey workers.
- Mobile retroreflectometers units (MRU) are attached to survey vehicles and these can take continuous measurements of pavement markings with the same level of accuracy as handheld units at normal traffic speeds and without the need for traffic management and lane closures. Data is collected by a computer in the survey vehicle, enabling road networks to survey more efficiently.
- There two types of MRU systems available
- Side mounted MRU. These are attached to the side of a vehicle and can only assess the edge or center line at same time.
- Front Mounted MRU. This is the latest innovation in mobile retroreflectometers and front mounted on a vehicle and records pavement markings across the full lane width including right (edge) longitudinal marking, left (center) longitudinal marking, center markings/symbols and absence & presence of RPMs.
Methods to Maintain Pavement Marking Standards.
The methods for maintaining pavement markings are detailed in FHWA-SA-14-017 Methods for Maintaining Pavement Marking Retroreflectivity.
These include –
- Visual inspections
- Measured retroreflectivity
- Expected service life replacement
- Blanket replacement
While three of these methods do not involve any measurements being taken, road authorities need to consider the litigation risk in the event of injuries or fatalities occurring where pavement marking visibility fell below the minimum standard and the authority failed to take any real data measurements or corrective action.
What should Road Agencies consider when buying a mobile retroreflectometer?
In buying a mobile retroreflectometer there are several factors to consider to be fully informed on the buying decision.
Mobile retroreflectometers Units (MRU) should meet the ASTM Standards conforming to 30-meter geometry.
- ASTM E1710-18. Standard Test Method for Measurement of Retroreflective Pavement Marking Materials with CEN-Prescribed Geometry Using a Portable Retroreflectometer
- ASTM E3320-21. Standard Test Method for Measurement of Retroreflective Pavement Marking Materials Using a Mobile Retroreflectometer Unit (MRU)
Accuracy and repeatability
The accuracy and repeatability of the system is important. Not only do you want to be confident that the system measures retroreflectivity accurately you want to be confident that if you repeated the survey over the same stretch of road on the same day or night in the same conditions that you would get the same results within an acceptable tolerance range when compared to a hand-held retroreflectometers, (Hand-held are the benchmark).
Ease of fitting to vehicle and security
Some Side-Mounted systems available require the mobile retroreflectometer to be fitted and integrated into the survey vehicle. This can obviously introduce additional costs and lengthy delays & restricts the use of the MRU to one vehicle. Other single line systems attach to the side of the vehicle using a complex network of bars, suction cups and strappings. A front mounted mobile retroreflectometer attaches securely to a standard 2” square center mount front tow hitch bar and can be raised to increase road clearance when not in use. It can also be quickly removed & refitted on additional vehicles & operational in minutes.
While mobile retroreflectometers are technically sophisticated measuring devices you should aim to choose a system that survey operators find easy to fit and operate. Some systems require operators to continually interact with the computer to mark changes of pavement marking type e.g., Single continuous line, dashed or double line, color while front mounted systems automatically detect line changes enable the operator focus on the road ahead.
There are typically two different formats of mobile retroreflectometer (MRU) – side mounted systems and front mounted systems.
- Side mounted systems (Single-Line) are typically positioned behind the driver or passenger door. As a result, they inevitably get dirt and debris from the road sprayed from the front wheels onto the lens of the retroreflectometer which will affect the retroreflectivity readings. Survey operators may need to regularly stop and check the lens and clean when required. On a busy section of road this can be dangerous for survey operators. Front mounted systems clearly avoid this problem.
- Side mounted systems may also require an element of precision driving from the center of the lane as the survey device has to be in proximity to the pavement marking it is measuring. Normal lane driving is required for front mounted MRU systems as the algorithms automatically track the lines and center markings.
Data Processing and Reporting
Due to the fact that mobile retroreflectometers perform continuous measurements there is a lot of data collected in a survey run. Different retroreflectometer systems have different ways of processing this data and some systems can require a lot of manual intervention, in preparing data files for processing, tying up valuable resources for prolonged periods of time. Some MRU systems come with Interactive Visualization Software which illustrate Survey Results on maps with pass/fail thresholds and HD video, all GPS stamped. This makes it easy & quick to make maintenance decisions & maximize budgets and taxpayers’ dollars.
Practical Usage Considerations
Like many things in life, you typically only really understand what it is like to use something when you have to live with it day in and day out. With mobile retroreflectometers there are some practical usage aspects that should be considered before you decide which system is best for you. Common complaints from current MRU survey operators include –
- the amount of time it takes to have the system setup and ready to survey each time.
- parking up in parking bays on retail parks or in multistorey car parks for a break or for lunch (a real problem if you have a side mounted system)
- navigating through toll booths to avoid damaging side mounted systems
- having to dry lenses of systems during wet conditions (particularly problematic for side mounted systems)
We believe and our many customers agree that we have the most advanced and most efficient solution to retroreflectivity measurement available on the market. The RetroTek-D Front Mounted MRU mobile retroreflectometer unit meets all the requirements & standards & maximizes data collection with no disruption to road users or road closures. This enables road authorities and survey contractors to get accurate retroreflectivity measurements across the full lane width in one pass, day or night, minimizing survey time and fuel costs. The ability to compare survey results over different years within our survey software helps authorities to plan and predict pavement marking maintenance requirements and maximize maintenance budgets.
These MUTCD changes are effective from 6 September 2022 and State and Local DOTs have a 4-year period to comply with the new rulings.
For Further information or a RetroTek demonstration contact:
Phone: (469) 619-0899