Safety Today S13 · Melisa Finley, P.E., and Gerald Ullman, Ph.D., P.E. ost roadwork to-day involves reconstruction, re-habilitation and maintenance occurring near lanes of traffi

S12 Safety Today

Researchers try to fi nd more eff ective ways to illuminate work zones

M Night work comprises many com-plex issues and a variety of challeng-es, which include lighting conditions, safety, quality, manpower availability and administrative considerations.

DIFFERENT WAYS OF SEEING IT

Lighting is one factor that must be properly addressed for night-time construction and maintenance activities, as it aff ects driver and worker safety, work quality, worker productivity and worker morale. Il-lumination guidelines for nighttime highway work have recently been developed based on past practices, existing illumination standards and regulations for construction, corre-lation to illumination standards for nonhighway construction tasks and subjective evaluations. The Manual on Uniform Traffi c Control Devices (MUTCD) has generally adopted

these lighting levels. Generally speaking, standard high-

way lighting, light from nearby busi-nesses or residences or light from conventional vehicle headlights are generally inadequate to properly light the areas where the work is per-formed. Thus, additional lighting is needed.

Typically, work-zone illumination is provided by three types of light-ing systems: temporary systems, por-table systems or equipment-mounted systems. Temporary systems use ex-isting or temporary poles to mount lights such that the entire work zone is lit. Portable systems combine the lights, power supply and pole into one device that can be easily moved from one location to another. Trailer-mounted light towers are the most common type of portable lighting system. Finally, equipment-mounted systems off er better mobility and are

Where the light is BETTER

Melisa Finley, P.E., and Gerald Ullman, Ph.D.,

P.E.

ost roadwork to-day involves reconstruction, re-habilitation and maintenance occurring near lanes of traffi c on existing roadways. More and more agencies are doing roadwork on high-volume facilities at night to reduce traffi c delays and complaints by the public that would typically be caused by doing the work during the day. In addition to several obvious advantages of nighttime work, such as fewer traffi c delays and cooler temperatures for equipment and materials, there also are certain dis-advantages.

Safety Today S13

useful to increase the level of lighting in front of or behind equipment.

The type of work-zone illumination used is highly dependent upon the duration of the work activity and geometric constraints. For mobile, short-duration and some short-term stationary operations, portable lighting may not be applicable since mobile opera-tions can cover long distances during a single work period, and for shorter-duration activities the setup and removal of portable lighting can take longer to perform than the actual work or could considerably increase the amount of time it takes to complete the work activity.

Thus, equipment-mounted lighting becomes more critical. For longer-duration activities, both portable and equipment-mounted lighting systems may be used. Also, in some cases fi xed temporary lighting may be used.

Geometric constraints such as limited or no shoul-ders, bridges, working adjacent to open lanes of traf-fi c, horizontal and vertical curvature and intersections also aff ect the quality of work-zone lighting being provided. Nighttime highway work on roadways with limited or no shoulders or on bridges may hinder or completely remove the ability to use portable light towers to illuminate the work area. In such instances, equipment-mounted lighting becomes critical.

NO WAY TO MEASURESo in the fi eld, how do we ensure adequate illumination is pro-

vided? Although specifi c criteria are available upon which to judge lighting adequacy, only a small portion of fi eld personnel actually use any type of light-measuring equipment to evaluate or verify lighting adequacy, glare or light trespass. One of the most critical weaknesses in the current state of the art in work-zone lighting is a lack of easy processes and tools to allow fi eld personnel to quickly measure and evaluate the adequacy of a lighting system. Presently, the only way that fi eld personnel can determine if the lighting provided meets such criteria is through an onerous data collection process, setting up a grid system and taking multiple measurements from illumination devices that typically require some degree of calibration each time they are used. Even if such a validation is conducted at one point in time and space (at the be-ginning of the work shift, for example) there is no guarantee that the system will continue to meet the requirements as the equip-ment and work activity moves along the roadway. This challenge is especially true if portable light towers are being used.

It is clear that methods need to be developed to facilitate the fi eld validation process for night work lighting systems. For ex-ample, tools that allow quick and standardized measurement of illumination around the work operation (possibly vehicle-mount-ed sensors) could be developed. In addition, it may be possible to use computer machine vision technology such as is used for video vehicle detection systems to quickly and objectively measure a work operation from multiple perspectives and provide easy-to-interpret outputs of illumination and other visual features such as shadows or glare.

LIGHTED EQUIPMENTRelated to the challenges in measuring and validating the il-

lumination provided within a nighttime highway work zone, the interactions between work vehicles and the light sources present can create shadows that fall onto key work areas. The severity and location of these shadows will depend on the following:

• Size and shape of the work vehicles; • The position, intensity and aim of the light sources; and• The movement of work equipment along the roadway.

Shadows can be especially problematic for fi xed lighting sys-tems because of the movement of the work zone. Of course, im-properly positioned equipment-based lighting can likewise create shadow problems that actually move with the operation. Presum-ably, many of the potential work areas around vehicles and equip-ment where shadows could occur can be identifi ed by equipment manufacturers, and equipment-mounted lights could be properly integrated into the design of the equipment.

For equipment already owned by an agency or contractor for which shadow lighting has not been taken into consideration, the challenge is much greater. In the fi eld, some work crews make d0 by pointing other vehicles with headlights on the work area to create adequate lighting for the workers. Unfortunately, ve-hicle headlights are not mounted a suffi cient distance above the roadway to avoid glare issues with either workers or with drivers traveling in lanes adjacent to the work area. In addition, the use of vehicle headlights pointed toward the work area and oncom-ing traffi c can create signifi cant anxiety with approaching driv-ers who can perceive themselves to be to the left of oncoming traffi c and not where they should be. Consequently, this practice should be avoided at all costs. Rather, the equipment should be retrofi tted with equipment lighting that allows it to be operated as intended.

Each piece of equipment and each task have unique task-light-ing requirements. Issues can exist with respect to where and how the lights are mounted on the equipment, ensuring that the pow-er supply for the lights is adequate and in limiting the amount of vibration of the lights themselves. Obviously, there are signifi cant constraints on where any equipment-mounted lighting is posi-tioned on the equipment. The lights must not aff ect the key func-tions of the equipment itself or of any other nearby equipment, nor must it interfere with equipment-operator interactions with the work crew on foot. Minimum mounting heights are needed to control glare to drivers and CONTINUED ON PAGE S19

workers, whereas maximum mounting heights may be needed to allow the lights to clear vertical obstructions such as overpasses. Lateral clearance also must be considered, especially when the work is adjacent to open lanes of traffi c.

Typically, alternators already installed on construction equip-ment can be used to power equipment-mounted lighting. How-ever, the alternator capacity for a particular piece of equipment controls the wattage of the lights and the voltage of the lighting system that can be powered. Furthermore, the other electrical demands of the equipment draw from this alternator capacity. Therefore, what is important is not total alternator capacity, but rather the spare capacity of the alternator available for retrofi tted lights. Some contractors have mounted separate portable genera-tors as power sources on construction equipment to operate 120-volt lighting systems.

Vibration is a major concern for some types of lights when mounted on construction equipment. Vibrations caused by con-struction equipment will vary by equipment type, mounting loca-tion on the equipment and use of poles or mast arms to elevate or extend the light. No single set of vibration parameters (amplitude or frequency) exist against which light performance characteris-tics can be measured.

If equipment-mounted lighting is not used to mitigate shad-ows, the number and position of portable light towers becomes especially infl uential on shadow eff ects. Shadows of fi xed objects, such as an overpass or sign structure, also can be created dur-ing nighttime work operations. Presumably, such shadows are fairly easily identifi able and remedied through repositioning of portable light towers in most cases. However, this issue could be problematic under special geometric situations, for example lim-ited vertical clearance within an overpass to allow portable light towers to be fully erected.

GLARING PROBLEMField personnel must remain vigilant against creating glare for

either the driver or worker when implementing lighting for night work operations. Unfortunately, an easily implemented quantita-tive procedure for measuring and verifying that glare is below a maximum threshold has yet to be identifi ed. Glare to drivers is an issue especially when the work activity is adjacent to open lanes of traffi c and at intersections, where drivers are approaching the work area from multiple directions. However, glare also is an im-

portant consideration when the work area is located adjacent to the roadway. Horizontal and vertical curvature also may increase glare to drivers, as well as decrease the illumination provided to the work area by portable light towers. It is important to remem-ber that glare issues can develop in real-time, especially if equip-ment moves along the roadway.

Portable light towers can provide illumination levels seven to 12 times the lowest adequate illumination level. This abundance of light can exacerbate glare problems for drivers if the light sources are improperly positioned. Such light abundance also may adversely aff ect drivers’ night vision and may decrease driv-ers’ ability to distinguish low-contrast objects such as workers or idle equipment. The vision of workers also may be impaired by bright and direct lighting sources. Low mounting heights, in other words close proximity to drivers’ and workers’ line of sight, used for some equipment-mounted lighting may result in glare to drivers and workers.

In most instances, glare can be reduced by physically moving the lights, altering the mounting height, re-aiming the lights or some combination thereof. However, aiming portable light tow-ers is typically a trial-and-error process that is not easily accom-plished with existing equipment. Wireless controls could be used to alter the aim of individual lights in portable light towers in order to reduce the time and eff ort needed to re-aim these de-vices. Other glare-control measures, such as cutoff lights, visors, louvers, shields, screens and barriers, also can be used.

Overall, it is imperative that lighting be provided for night-time highway construction and maintenance activities. However, highway agencies and contractors must be cognizant of the many challenges that exist in providing work-zone lighting. Making agencies and contractors aware of possible mitigation strategies to address these challenges is an important fi rst step in minimiz-ing the adverse safety consequences of improper lighting systems and implementations. ST

Finley is an associate research engineer at the Texas Transportation Institute. Ullman is a senior research en-gineer at the Texas Transportation Institute.

Safety Today S19

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CONTINUED FROM PAGE 13 WORK-ZONE LIGHT

PAVEMENT MARKING

special needs of work zones. For instance, they evaluated an ex-perimental “removable” marking that uses a patented liquid re-mover to wash away the markings instead of traditional methods that often damage the roadway surface leaving “ghost” markings, which can make it diffi cult for drivers to decipher the correct travel path.

Recent TTI research also has focused on how to select the ap-propriate pavement-marking material for work zones. On one hand, it is desirable that the material selected be durable enough to last for the duration of the temporary change in alignment for that particular project or project phase. On the other hand, since the application is temporary and will eventually be removed or covered, it is desirable to use as inexpensive a material as possible with an anticipated service life for that particular application that simply exceeds the temporary duration that will be needed.

TTI researchers developed an objective methodology for se-lecting the most appropriate pavement-marking material for work-zone situations based on the duration of the project or project phase for which the marking is needed, type of pavement

surface the marking will be placed on and durability of the various marking materials available for use in work-zone situations.

EVERYTHING IS BEING DONEThe research that goes into pavement markings is paying off in

many ways. The pavement markings you see on the road are made with long-lasting materials, installed with state-of-the-art tech-niques and being measured with appropriate test methods that have evolved with time. TTI’s facilities and breadth and depth of relevant expertise have been key elements to the progress seen in the pavement marking world. ST

Carlson is an associate research engineer and the head of the Operations & Design Division at the Texas Transpor-tation Institute.

LEARNMORE For more information related to this article, go to:

www.roadsbridges.com/lm.cfm/rb060806