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Nighttime Visibility

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Methods for Maintaining Pavement Marking Retroreflectivity

CHAPTER 4. CONSISTENT PARAMETERS PROCEDURE – VISUAL NIGHTTIME INSPECTION METHOD

Introduction

The consistent parameters nighttime visual inspection maintenance procedure can be used by agencies to conduct nighttime visual inspections without requiring the need for specific markings or retroreflectivity measurements. Rather than using calibrated pavement markings, the consistent parameters nighttime visual inspection procedure relies on the judgment of an inspector that is at least 60 years old. The minimum retroreflectivity levels outlined in the MUTCD are based on research that is based on the visibility performance of older drivers. Therefore, the pavement marking visibility viewed by an inspector who is at least 60 years old can be thought of as a surrogate for minimum maintained retroreflectivity.

Using this procedure, it is possible to assess more than just the retroreflectivity of pavement markings. Inspectors may identify other damage, such as excessive wear from turning movements. In addition, they can examine current pavement markings to be sure they continue to meet MUTCD and other policy requirements. This procedure requires a minimal investment of resources on the part of the agency, although there is a need for a record-keeping system for inspection data and the potential for higher labor costs where overtime pay is required. While visual inspections will reveal night visibility problems not discernable under any other method, they are subjective and hence more difficult to tie to a benchmark value of retroreflectivity. As a result, agencies using visual inspections must establish procedures to provide consistency in inspections. This implies the need for training programs and inspector certification.

Background

The consistent parameter procedure is a visual inspection method that shares some elements of the calibrated visual inspection procedure. The main difference is the inspector's age and ability to perform the method without calibrated markings or a retroreflectometer to measure the calibrated markings.

This consistent parameters procedure uses inspectors aged 60 years or older to observe pavement markings during the nighttime to assess the overall pavement markings appearance and determine if they need to be replaced. The observation is typically done through the windshield of the vehicle at or near the speed limit of the roadway. It is desirable to have a dedicated driver so that the inspector can concentrate on the markings.

The key to this procedure is having trained inspectors. While there is no nationally recognized training course or certification for pavement marking inspectors, agencies should provide some form of training before nighttime inspections are performed. The FHWA will provide inspection training tools to the LTAP and TTAP Centers.

One way to perform the training is to teach the inspector (particularly if an agency is using a layperson) what types of markings to evaluate. The MUTCD does not require that all pavement markings meet the minimum retroreflectivity levels. The minimum retroreflectivity levels only apply to certain white and yellow markings as described in Appendix A. Training should also cover the agency's guidelines and procedures for conducting nighttime inspections, including any necessary documentation. This helps facilitate an inspector's preparation before beginning the nighttime inspections.

General Procedures

The consistent parameters procedure is conducted using a two-person crew. While the driver focuses on the driving task, the inspector (aged 60 years or more) evaluates the pavement markings and records the appropriate information. Those markings judged by the inspector not to meet his/her driving needs should be replaced (i.e., Can the "older driver" see the markings far enough in advance to make appropriate decisions and maneuvers?). Although not recommended, an alternative to a two-person crew is to use one person with a tape recorder or mounted camcorder for recording notes. The condition assessments need to be made at the time of the inspection, so any video recording should not be used later for determining the condition of the markings. Video technology is not yet available that can provide the necessary quality to be used in assessing retroreflectivity.

Details

A policy should be developed by the agency for consistent inspections. Unlike the calibration markings procedure, this procedure requires no equipment like a retroreflectometer. The only requirement is that the inspector is at least 60 year old and the inspection takes place at night. In addition, the inspection vehicle headlamps should be properly aimed and set to low beams during the evaluation. The inspection vehicle can be any type of passenger vehicle, although a passenger car is preferred as it most closely matches the research parameters. The inspections should occur at or below posted speed limits and from the travel lanes. It is helpful to plan the routes and frequency of inspections early and to document as much of the process, including the inspection results, as possible. As noted earlier, this can help alleviate agencies' concerns over tort liability.

Linking to Minimum Retroreflectivity Levels

Minimum retroreflectivity levels are incorporated into this procedure by using inspectors of the same age as those who participated in the supporting research used to develop the minimum pavement marking retroreflectivity levels in the MUTCD. An objective of the MUTCD language is to establish minimum levels of nighttime pavement marking performance based on the visibility needs of nighttime drivers, especially older nighttime drivers, and this procedure provides a technique to do just that.

Advantages

One of the major benefits of using the consistent parameters nighttime visual inspection procedure is that it has the lowest equipment, administrative, and fiscal burdens. Many agencies already perform some type of periodic pavement marking inspection, although not all inspections are performed at night. This procedure also has a unique feature in that the pavement markings are viewed in their natural surroundings. Thus, the overall appearance of the pavement marking and the ability of the pavement markings to provide information to the driving public can be assessed.

Another advantage of the consistent parameters nighttime visual inspection procedure is that it has a low level of unnecessary replacement and waste. Only those pavement markings identified as needing to be replaced because of low retroreflectivity levels are replaced, assuming that the inspection frequency is appropriate.

Concerns

This procedure relies on the judgment of the inspector. It is the most subjective of all approved methods. While it can be used effectively, it may be challenging to use this method to enforce contracted minimum retroreflectivity levels that come with disincentives if the markings fail a specific threshold before a set period of time.

Visual inspections of pavement markings supplemented with raised pavement markers (RRPMs) can be difficult. The brightness of the RRPMs is usually much higher than the pavement markings and therefore it can be difficult to judge the pavement marking retroreflectivity.

Pavement markings on either side of the inspection vehicle can be evaluated during a visual inspection. However, pavement markings that are not adjacent to the inspection vehicle cannot be evaluated during a visual inspection. Therefore, for multilane highways, more than one pass is needed to inspect all of the longitudinal markings (per direction).

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Page last modified on February 1, 2017
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