英文翻译
原文：
ABSTRACT
This paper discusses the implementation of semi-permanent, high-mast pole-mounted lighting for nighttime road work construction and maintenance based on an installation along Interstate 90 in Albany, New York. The high-mast lighting system met state lighting performance specifications. There were no recorded accidents at the site during the construction period. Although this is largely attributable to roadway closures allowed during part of the project, the consensus of the contractor and transportation agency is that the lighting contributed at least in part to an increase in safety. The cost of the high-mast lighting system was approximately 16% higher than the estimated cost of the portable light towers. Despite the higher estimated cost of the high-mast lighting system, the economic and societal benefits appear considerable in this particular location, namely an urban, heavily traveled throughway. In particular, this lighting approach probably allowed the duration of the construction period to be shortened, leading to a reduction in worker and driver risk exposures and to a reduction in traffic delays for motorists. An approach to identifying projects where this lighting technique might be warranted is presented.
INTRODUCTION
documented翻译
Semi-permanent, high-mast (70 ft.) pole-mounted fixtures were used by    a construction contractor hired by the New York State Department of Transportation (NYSDOT) to illuminate nighttime road work construction and maintenance along a three-mile stretch of Interstate 90 (I-90) in Albany, N.Y., as an alternative to the more common portable light towers (1). The high-mast lighting was installed prior to construction work and removed after the construction project was completed, about seven months later. Freyssinier et al. (2) documented the high-mast lighting system and its performance in terms of photometric performance, visibility and glare. The high-mast lighting system was found to have performed well and as intended. The installation provided a level of illumination sufficient for performing the maintenance and construction activities at the site (3), with less pronounced shadows and relatively low glare. The purpose of the present paper is to discuss approaches to identifying if and when this lighting approach can be appropriate for a highway construction project. Issues regarding safety, economics and environmental impacts are discussed, and an approach to warranting semi-permanent, high-mast nighttime construction lighting is offered.
To decide if and when semi-permanent high-mast lighting is feasible for highway construction work, one must consider safety, economics and environmental impacts. These issues are discussed, in turn,
in the following sections.
SAFETY
Crash Risk Factor
When the contractor hired by NYSDOT to perform road work along I-90 proposed using semi-permanent, high-maslighting for nighttime construction work, safety
engineers analyzed the proposal against the concern that most (aboutwo-thirds) of the proposed high masts would be located within the 30 ft clear zone desired for this highway. The clear zone is defined (4) as the area outside the paved roadway area where a vehicle could safely travel if it left the road. Acknowledging that portable lighting for nighttime roadway construction work is nearly always located withinthe clear zone and in fact often closer to drivers, NYSDOT engineers concluded that high-mast lighting probably had a lower risk factor than portable light towers, and authorized the contractor to proceed with the installation and roadwork, based on the following reasons:
While in use, portable light plants are almost always located inside the clear zone. About one third of the 108 high-mast poles proposed could be located outside the clear zone without compromising lighti
ng quality. The lower number of poles in the clear zone, compared to the number of conventional, portable units needed to illuminate a portion of the highway, was thought to weigh against the added risk of drivers!ˉ constant exposure to semi-permanent poles during both daytime and nighttime. Howeveradditional safety features were recommended, such as traffic barriers, guards and crash cushions.
High-mast poles avoid the high-risk exposure of workers every night during setup and removal of the conventional portable light units. In the I-90 project, it was estimated that at least 8250 worker-hours of high-exposure would be eliminated. Time savings in the mobilization of portable lights meant night construction could be completed in 222 days rather than 275, reducing the work to one construction season. NYSDOT!ˉs authorization was conditioned on tremoval of the high-mast poles by winter shutdown, regardless of the contractor!ˉs work accomplishments.
Worker Safety Implications
While the conventional light towers are extremely useful because of their portable nature, there are a number of known issues regarding the difficulty of their installation, operation, and maintenance. First, there are a large number of warnings associated with most products (during setup, operation, mainten
ance, stowing, and transportation). Second, the two main risks associated with the use of portable light towers are the interaction of workers with traffic during setup and removal when both conditions represent a high risk of collision between workers and drivers, and the setup of light towers near power lines. Although there are no published statistics, it is reasonable to believe that crews are at increased risk of injury or fatality when raising a mast near power lines. It follows that by having a semi-permanent lighting installation, much of the risk mentioned would not be present.
TABLE 1 Estimated Operational Cost of Portable Light Tower Installation Estimated number of portable light towers required 120*
Daily setup and removal cost
Number of crew members in charge of setup and removal 10 Estimated number of hours to setup and remove light towers, per night    3
Total worker hours per night 30 Estimated cost per hour (base rate + benefits + overhead & profit) $40
Total setup and removal cost per night $1,200
Daily operational cost
Hourly operational cost per light tower (fuel, oil, regular maintenance, etc.) $3.60 Estimated daily cost per light tower (@ 6 hours per night) $21.60
Daily rental cost (@ $990 per month rent) $33
Total operational cost per night (assuming contractor owns 100 towers and rents 20) $3,252
Total cost per night (setup, removal, and operation) $4,452
Estimated duration of project in days 275**
Total cost to provide lighting with 120 portable light towers $ 1,224,300
120 towers is estimated to be required to illuminate a sufficient portion of the work zone at one time.
The duration was estimated to be 40 days shorter using the high-mast system.
Another potential safety benefit of high-mast lighting that could not be quantified precisely was the fact that warning signs, signals, and other materials for guiding traffic through the work zone could be set up each night under lighted conditions. In comparison, such warnings are typically set up by workers in advance of having the conventional light towers operational.
The Environmental Protection Agency recommends a maximum noise level of 75 dBA in work environments for hearing conservation (5). Though the generators that power most of the commercial light towers typically have a noise level rating of 71 dBA, the large number of light towers (each with its own generator) and their relatively close spacing (typically about 100 ft between units) can cause noise to add up to levels that could be more than the maximum recommended. During this project, five large generators powered the entire high-mast lighting installation; each generator was located as far from the work area as possible. Each of these generators was rated at 71 dBA, dramatically reducing noise levels throughout the site. Workers of this project commented that the noise reduction enabled them to hear vehicles approaching, again greatly decreasing their risk of injury by a moving vehicle or machine.
Finally, by using high-mast lighting with remotely located generators, workers were not as exposed to the fumes and harmful pollutants that result from the generators adjacent to each portable light tower and that might cause headaches, fatigue, and potential heart problems (6).
ECONOMIC ANALYSIS
Tables 1 and 2 summarize the economics of a lighting system using the portable towers and the high-
mast system. Despite the higher estimated cost (approximately 16% higher) of the high-mast system as outlined in these two tables, there were several positive economic implications that resulted from the use of high-mast lighting. One significant benefit was the time saved every day from not having to setup and remove the portable light towers. This time could be used performing the contracted construction work rather than setting up lighting equipment, probably contributing to
the ahead of schedule completion of the project. In this project, the estimated cost of setup and removal of portable light tower added up to $330,000 (30 worker-hours per night at $40 per hour, for 275 days). For larger jobs this cost would increase considerably.
TABLE 2 Estimated Operational Cost of Semi-Permanent High-Mast Lighting Installation
Number of high-mast poles installed 108
Number of 250-kW generators installed    5 Installation costs
Estimated installation cost per pole $2,844 Estimated installation cost per kW of generator capacity $24.50
Total estimated installation costs (poles and generators) $337,777 Lighting equipment rental
Estimated rental cost per pole with four luminaires $5,500
Total lighting equipment rental (for the duration of the project) $594,000 Generation costs
Estimated purchase cost per kW of generator capacity $200 Estimated total generators purchase cost $250,000 Operational cost
Hourly operational cost per generator @ 55% load (fuel, oil, regular maintenance) $25.83
Total operational cost per night (@ 8 hours per night) $1,033.20 Estimated duration of project in days 235*
Estimated total operational cost over the length of the project $242,802
Total cost to provide lighting with 108 high-mast poles $1,424,579 Incremental cost over portable lighting towers $200,279 (16% higher)
The duration was estimated to be 40 days longer using the portable light tower system.
It should be noted that for the lighting installations summarized in Tables 1 and 2, the semi-permanent
high-mast installation was able to illuminate the whole length of the project, on both sides of the road, while the portable units were capable of illuminating a short section only at a given time. At an approximated spacing of 100 ft, 120 portable light towers can illuminate only a limited section of the road on one side only. In order to provide lighting to the whole length of the project with portable light towers, it would be necessary to use about 530 units, increasing the operational costs by approximately a factor of 4. As this is not a realistic application of portable light
towers in practice, this comparison was not made.
The contractor estimated a 40-day reduction in the planned duration of the project. While not possible to quantify in terms of economic benefits, the benefits for roadway users (in terms of avoided traffic delays during setup and takedown) are also apparent. An accurate calculation to single out the contribution of the lighting system is not possible because NYSDOT allowed the contractor to close the entire length of one side of the road overweekends, effectively increasing the work time from 21 hours per weekend (Friday, Saturday and Sunday nights, at seven hours per shift) to 60 hours (Friday night to Monday morning with crews working three shifts).
As described above, it was not possible to estimate the relative impact of the lighting and the road clos
ure separately, but informal discussions with the contractor revealed the opinion that the lighting was a significant part of this reduction. The reduction in work time also probably translated into savings caused by reducing delays to drivers navigating through the work zone. It was assumed that improved visibility by reducing glare (1,2) also yields safety benefits to drivers as well, but the strongest testimonials to safety were from the people involved in the project who described an increased perception of safety due to the higher light levels and uniformity. In general, these factors, taken together, were thought by the NYSDOT contractor to more than outweigh the initially higher economic cost of the high-mast system. The contractor and a few workers interviewed during the construction work agreed that the higher light levels and uniformity allowed them to work at a much faster pace, and possibly improved the quality of their work at the same time.
Relamping could also increase the cost of the light tower system relative to the high-mast system, as well.Although the lamps used in either portable units or high-mast luminaires have nominally the same life, the working conditions of the lamps in the portable units (e.g., constant vibration, raising and stowing the mast, transportation from yard to site) would likely promote a shorter life (7).
Another important aspect of this project was the fact that no injuries were reported (8). The people involved in the project believed that the higher and more uniform light levels (1,2) were positive contrib
utions to safety. While direct comparisons of safety with projects of similar magnitude, location and duration as the present construction project were outside the scope of the study described here, such comparisons would be helpful in elucidating the role of the lighting installation in contributing to increased safety.
ENVIRONMENTAL IMPACT
The primary environmental impact of the semi-permanent high-mast lighting system discussed here is that of light pollution. Light pollution can be defined and discussed in three different ways: sky glow, light trespass and glare (7). Each is related to the amount of light leaving a site (in this case the roadway right of way), but each is measured in different ways.
Sky glow is simply the amount of light leaving a site. Sky glow will limit observations of astronomical objects due to obscuration by the light scattered into the atmosphere. The computer simulation model developed by Freyssinier et al. (1,2) to characterize the high-mast and portable lighting systems was used to calculate the