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63 A significant concern and perceived disadvantage of nighttime construction is that construc- tion costs are higher. However, a careful review of past studies of nighttime construction costs indicates that, while in certain circumstances costs are higher, in most cases, nighttime construc- tion costs are comparable or even less than those experienced with daytime work. A study sponsored by FDOT using bid item cost comparisons found no cost differential on individual items, and the study noted that the total program cost was less for work at night than for work during the day (Ellis and Kumar 1993). While high-cost item variations were found between the projects, standard deviation measurements showed the unit costs were more depen- dent on project-related conditions than on changes for nighttime or daytime work (Rebholz et al. 2004). The study did not include an analysis of competition for the work, so it is difficult to identify specifically why the total project cost was lower. Ellis and his team of researchers completed sev- eral other studies of nighttime construction, and their final conclusions were that cost, quality, and productivity are not significantly different between daytime and nighttime operations (Ellis et al. 1991 and 1993). A study by Hinze and Carlisle (1990a) did find that âcontractâ costs were 9 percent higher for night work because of increased costs associated with the following: ⢠Augmenting traffic control. ⢠Need for lighting. ⢠Worker overtime or premium pay. Key Take-Away For most projects, the cost of work items is not dependent on whether the work is performed during the day or at night. Project-specific conditions are the drivers that cause price differentials between daytime and nighttime work. Additional costs were sometimes incurred because of material delivery at special times, inspec- tion, and operating concrete and asphalt plants beyond the normal work day. These potential additional costs are a clear indicator that STAs should carefully consider the requirements for nighttime traffic control and lighting. The contract cost increase will be greater for small projects where the overhead cost of lighting and traffic control must be spread over fewer bid items. Despite the increased costs for traffic control and lighting work items, road user costs experienced by the public are typically reduced when work is performed at night. In addition, lower nighttime traffic volumes can result in C H A P T E R 7 Cost
64 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity convenient and faster delivery of materials to the jobsite and transport of waste from the site, potentially reducing the overall project cost. In summarizing the situation, the Transportation Research and Development Bureau of the NYSDOT concluded the following (Elrahman 2008): ⢠User cost decreases when work is performed at night because of the elimination of delaysâ businesses experience less disruption as well. ⢠There is no consensus on whether construction costs increase or decrease as a result of performing work at night. This seems to be dependent on project size and specific work operations. Key Take-Away Work Tasks Affect Costs Even with good lighting, lifting operations are very difficult at night. At about 15 ft above the operatorâs location, objects disappear into the dark sky. The contractor for the Woodrow Wilson Memorial Bridge widening in the early 1980s is of the opinion that the nighttime crane work led to significantly reduced productivity and increased costs. The following sections of this chapter address the factors that influence nighttime construc- tion costs, considerations in estimating nighttime costs, analysis of nighttime costs compared to daytime costs, and best practices in minimizing nighttime construction costs. Factors Influencing Nighttime Costs Little consensus exists among transportation personnel or between agencies on the specifics of nighttime cost variations and common items that contribute to the perception that night- time construction is more costly. A study by IDOT found that 76 percent of the STAs have the perception that nighttime work is more expensive, with administrative expense being a major contributor to the increase (Al-Kaisy and Nassar 2002). Different researchers have, however, concluded that factors other than administration contributed to the increase in nighttime con- struction cost. Construction Costs Following are the costs directly related to performing the work items of a contract and how they are influenced. Labor Cost Nighttime operations may require overtime or a labor premium shift differential. Either one increases hourly labor costs and can also increase agency costs, but such increases are often off- set by better productivity. Better productivity derived from more efficient operations leads to reduced contract costs. Union agreements are a labor cost factor that must be carefully consid- ered and addressed when an agency proposes a nighttime work schedule. A second component of possible labor cost increases is the actual time available during a shift to perform work. If it is necessary to establish and remove traffic control for a night shift, this affects labor cost. The workforce may have to be paid a standard eight-hour shift but cannot begin work until the traffic control is in place and must quit productive work early so the traffic control can be removed and the travelway reopened. In such situations, the worker is paid for a full eight-hour shift but works a shorter time period (Rebholz et al. 2004).
Cost 65 Equipment Cost Because of the lost production that would result if a critical machine experienced a break- down during a night shift, contractors often place standby machines on nighttime projects. Machine downtime can also have a more significant loss-of-productivity impact at night due to the unavailability of parts or a replacement rental (Rebholz et al. 2004). An additional cost may be the expense of attaching special light apparatuses to operating equipment. Material Acquisition Procurement of materials and supplies is not always possible after the normal business day. Such conditions may force the contractor to have several shifts for transporting materials or create a necessity for storage areas. If not owned by the contractor, concrete and asphalt plants may charge extra for operating at night. Hancher and Taylor (2001) found, however, that because of less con- gestion, easier delivery of materials to the project resulted in decreased costs. Nighttime concrete and asphalt work can be a problem in cold climates, while in warm climates it can be an advantage. Tip The material cost issue is driven more by the quantity requirements. Night work for asphalt or concrete can be very expensive when small quantities are involved (CFLHD (Central Federal Lands Highway Division) 2008). Traffic Control Nighttime traffic control often requires additional elements beyond those necessary when work is conducted only during the day. A study for the Virginia Department of Transporta- tion (VDOT) recommended specifically: (1) improving the visibility of traffic control devices, (2) improving the visibility of workers, (3) improving the visibility of work vehicles, (4) decreas- ing traffic speed and increasing driver attention, (5) decreasing glare from work lighting, and (6) instituting measures to manage traffic queuing (Cottrell 1999). Tip Consider nighttime full- or partial-closures as alternatives to resetting traffic control. If night work requires extensive mobilization of traffic control devices, construction equipment, workers, and demobilization at the end of the shift on a nightly basis, the project will have significantly higher traffic control costs. While this situation adds to traffic control costs, the time required to install and remove the traffic control also limits the shiftâs productive work time (Bryden and Mace 2002b). Portable concrete barriers, which would not be needed for daytime work, may be necessary for nighttime traffic control to protect workers when traffic volumes and speeds are relatively high. The NYSDOT recommended early on, if feasible, a total shutdown and reasonable detour or, without a reasonable detour, that work be done behind barriers in traffic (NYSDOT 1991). Good planning during project development is an effective way to limit and manage traffic control costs. Lighting Expense The provision of nighttime lighting is a cost not experienced with daytime work. Lighting is a critical necessity for a safe work zone and productivity, and it can have an impact on the quality of the work. Schedule Cost Effect The project duration affects total construction costs. Working at night may allow a project to be completed sooner than if it had been accomplished during mid-day off-peak work hours
66 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity over more days. Alternatively, a night schedule with a partial closure might be chosen over a total closure during the day and this could increase the projectâs duration (Hinze and Carlisle 1990b). Indirect Cost The agencyâs project staffing cost must be carefully considered. It may be necessary for the STA to pay inspectors and quality control laboratory personnel a premium shift differential. Night- time operations may, moreover, require the use of law enforcement and other personnel at times or in additional numbers. Training about nighttime safety issues and safety practices may be needed for workers who have not had such training or who have not had such training immediately prior to the project. Plan- ners, designers, and field staff of both the highway agency and the contractor involved are appro- priate participants in training for nighttime work-zone safety (Bryden and Mace 2002a, 2002b). Key Take-Away Agency decision makers need to be available at night and it may be necessary to have project consultants on call as well. The ability to get answers is one of the contracting communityâs major concerns when bidding and planning nighttime work. It is best that on-site project meet- ings also be held at night so everyone has a clear understanding of the work environment. Other Costs Besides construction costs, other types of costs relevant to nighttime construction are road user costs, business costs, and possibly costs resulting from accidents in the work zone. Most transportation agency personnel believe nighttime construction results in reduced road user costs. Given that traffic volume is less at night, delay costs go down and therefore decrease vehicle operating cost. Moreover, by conducting work at night, many businesses are closed and do not suffer inconve- nience compared to when construction activity is conducted during the day. However, this effect is dependent on business type. Most studies show nighttime accidents are less frequent. This is primarily because of less traf- fic at night. However, nighttime vehicle collisions can be more severe because of alcohol, illegal and legal drugs, and fatigue. According to national fatal collision data for 2001, 50 percent of all fatal highway accidents occur between 6 p.m. and 6 a.m. Forty percent of the fatal nighttime collisions occur between 6 p.m. and 6 a.m. on Fridays and Saturdays, and if Sunday is included the percent increases to 56. This makes an argument for scheduling nighttime work on a four-day pattern of Monday through Thursday nights. Key Take-Away The key to economical nighttime construction is competition. Structure the bid package so it entices contractors to bid. Through conversations with subcontractors and suppliers, contrac- tors have a good feel for the bidding environment and, with competition, they may not put extra markup on a nighttime project. Considerations in Estimating Nighttime Costs The effect on productivity and, therefore, project cost is a function of the type of work and continuous work hours allowed. In addition to the work hours issue, decreased visibility and greater difficulty communicating with supervisors and/or technical support staff are two other factors that can have a negative effect on productivity and increase cost.
Cost 67 Another factor that may have a negative effect on productivity is the longer setup/take-down times for traffic controls and lighting. A project development process that considers work-zone lighting carefully and minimizes the necessity to re-establish traffic control repeatedly will decrease the cost of nighttime work. Some items of work can be performed faster at night, while others, such as painting, are dif- ficult because of shadows. Before writing the project special provisions, STA staff should go through each work activity of the project to identify which items should not be a problem to accomplish at night (such as paving and hauling dirt) and which will be difficult to perform at night (such as erecting steel girders). After completing this step on a few projects, agency staff will become aware of the work items that can typically increase project cost and possibly find ways to allow such work during daytime hours. Erecting steel girders at night can be very tricky because it is difficult for crane operators to judge distance against the dark sky. On the other hand, bolting up steel can be accomplished efficiently at night because it is a close-range activity. On a project in Washington State, a 10-ft deep girder bridge over the Interstate was bolted up in a single night shift. Key Take-Away To control project costs, STAs need to dedicate much more effort to planning. The record of the items affecting nighttime construction cost should be included in a check- list and the list should be available to those responsible for estimating project cost. MDOT has estimate-preparation questions specifically for nighttime work, with one of them being the lighting costs (see Figure 7.1). In addition to the checklist, MDOT includes nighttime cost items within its project-scoping sheet, together with other temporary traffic maintenance items. Agencies can have different means and methods for estimating nighttime project costs and the items that are included in the estimate. Consequently, specific work items required for working at night may be included in a lump sum cost item. When lighting and traffic control for a nighttime project are bid as lump sum nighttime costs, it is very difficult to produce accurate future cost estimates from that lump sum, given that the historical cost breakdown is not available to the estimator. Furthermore, when nighttime items are lumped, it is impossible to quantify nighttime/daytime cost differences later. Consequently, this research team recommends that lighting be specified and paid by types of lighting equipment: mobile light towers; balloon lights; semi-permanent high-mast lighting systems; and light towers on paving, milling, and finishing machines. Data from such pay items will provide cost information for estimating future projects and will make it easier to control the costs during the construction phase of the project. Figure 7.1. MDOT road cost estimating checklist.
68 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Analysis of Cost Variations for Daytime versus Nighttime Work It is often difficult to determine the true cost difference between daytime and nighttime con- struction projects because of the bidding and costing processes involved. Most agencies bid projects on a unit-cost basis. Such bid prices include the cost of labor, equipment, and materials for each work item. At the time of the bid, the project specifications indicate when (day or night) the project work will be performed. Agency officials are also aware that different contractors use different cost methodologies and different pricing strategies in preparing project bids. Consequently, officials say that they cannot readily determine the cost differential for nighttime construction or the cost of comparable work performed as a nighttime, as opposed to a daytime, construction project. Several studies on cost differentials indicate that lighting has the highest impact on the cost differential. Work quality and safety both require good lighting and visibility. Other project tasks/items, such as traffic control, inspection, and labor pay premiums, do not show significant differences in cost when performed at night. Material costs may be increased or decreased depending on two factors: whether or not con- tractors have their own plants and the magnitude of quantities (not total quantity) required per operation. For example, a nighttime project that requires the contractor to place minor quan- tities of concrete or asphalt on a repeating basis will likely incur major cost differences when compared to such a situation happening during a normal work day when it is easier to schedule deliveries. Individual work item cost can be significantly different when comparing cost for daytime and nighttime work. However, higher or lower work item cost differentials are not consistent across projects. These differences may be more a case of project location (i.e., remote areas versus urban locations) and of the experience and/or abilities of the contracting pool with nighttime work. The number of nighttime project offers to contractors also affects prices. A continuing series of nighttime projects should decrease bid prices as contractors gain experience, a reliable work- force, and also purchase the special equipment necessary for nighttime work, such as light plants or special lights for machines. The magnitude of the cost differences between daytime and nighttime work items depends on a variety of factors besides the issue of daytime versus nighttime. Traffic volume and the nature and complexity of work, as well as schedules, were found in some studies to have more of an impact on cost than the time of day when the work was performed. The conclusion is that, while nighttime scheduling can affect cost, many other factors are often the primary cost drivers. Key Take-Aways When estimating nighttime construction work, it is necessary to consider all conditions affect- ing the work carefully. In respect to nighttime work, the effect of repeatedly needing small quan- tities can be much more significant in increasing cost than in the case of daytime work. At the same time, ease of delivery can improve production and reduce cost. Lighting, shift-differential pay, and, possibly, safety equipment may increase item and total project cost, but this effect can be mitigated by better productivity. Faulty Analysis The New York State Comptroller (1999) compared daytime and nighttime costs of 20 project components from six nighttime construction projects. The average price for each item from all
Cost 69 bidders was computed, rather than the price from only the low bidders for each component. As expected, including the high bids tended to increase the cost of each component for nighttime construction. The study found that costs for nighttime construction ranged from a negligible amount to as much as 20 percent higher than the costs for similar daytime operations. In this study, the comparison was based on the arithmetic average cost for each component to a weighted average cost of these same components. Therefore, a follow-up audit by the state comptroller compared weighted averages for each component with the weighted average for all projects. The audit analysis found that costs associated with nighttime construction were generally not as high as indicated in the original study. As an example, the cost of asphalt was found to increase by only three percent versus 16 percent from the previous report (New York State Comptroller 1999). As the New York State Comptroller found, the analysis used in many studies of nighttime construction costs exhibits weakness in its methodology. Therefore, STAs should implement sys- tems based on sound methodologies to accumulate pertinent cost data for estimating future nighttime projects. Best Practices on Minimizing Cost Many options are available to minimize the increase in total project cost or even item cost for working at night. The key is to institute careful planning early in project development. For example, a lane-closure option should be considered against a total road closure. Different traffic control costs and very different productivity effects are involved in planning decisions. Closure options affect productivity and project duration, which, in turn, affect total project costs. Options must be evaluated based on total cost to accomplish the work and convenience to the public. Once the need to perform work at night is identified, agencies should carefully review the material quantities required and whether or not a continuing sequence of nighttime jobs is feasible. As discussed in Chapter 5, Productivity, the CA4PRS tool is very good for modeling construc- tion operations to evaluate productivity and cost. CA4PRS can be used to investigate different lane-closure schemes and different rehabilitation strategies. The experience of WSDOT in recon- structing two lane-miles of portland cement concrete (PCC) pavement on I-5 in 2005 through downtown Seattle provides excellent insights into the use of this tool. Resource A review of the WSDOT I-5 project and use of CA4PRS can be found at: http://pavement interactive.org/index.php?title=WSDOT:CA4PRS_Case_Study_1-_I-5_Olive_To_James/Project_ Background. Traffic control and lighting can be major contributors to any increased cost for night work. Therefore, a continuing sequence of jobs allows contractors to spread the ownership cost of the required lighting equipment over more work hours and should reduce project cost. In addition, the contractorâs nighttime workforce does not need to be retrained repeatedly. With a single project, the agency is continually paying for each contractorâs learning curve to attain efficient nighttime operations. Experience with nighttime operations by both STAs and contractors has proven in many loca- tions that early estimates of increased cost can be reduced significantly, especially by developing traffic control plans that maximize productive work time.
70 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity An important cost driver may be weather conditions, which can limit paving operations. Cooler nighttime temperatures can be better for concrete paving, but low temperatures may limit asphalt paving operations. Clearly, nighttime construction does not need to cost more when applied to the appropriate setting with good planning. Tip Frequently, both the traffic control and the construction operations at night are very com- plex, and the two operations must be staged in the proper sequence to maximize efficiency and safety. Therefore, traffic control plans should be subjected to a careful review to ensure that all essential elements are included and that non-applicable elements are excluded. Tip When considering nighttime work, be sure to allow closures that provide a minimum of eight hours of actual work time. It takes almost as long to setup and tear-down for five hours as it does for eight, so an eight-hour shift yields a better setup/tear-down to actual work ratio. Tip If traffic volumes are lower than predicted at either end of the work shift, it may be acceptable to lengthen the work shift with little or no additional impact on traffic. Lengthening the shift generally improves productivity and reduces costs. Tip Consider contract specifications that require permanent project lighting be installed early in the work schedule. Conclusions The important nighttime cost impact factors are lighting expense, additional or different traf- fic control measures, and labor premiums for overtime or shift differentials. Other causes of possible increased costs are premiums necessary to make suppliers available, indirect costs such as training in nighttime safety practices, standby equipment, and schedule cost effects. However, some of these costs can be decreased significantly or offset by implementing a continuing sequence of nighttime jobs or through good project planning early in project development. The literature provides cases of disagreement as to whether nighttime construction costs are actually greater than those experienced with daytime work. The New York State Comptrollerâs audit of cost experiences in that state pointed out that most cost comparisons have used flawed methodologies. Therefore, it appears that, in most cases where higher costs were reported, mul- tiple factors affected cost besides the nighttime work issue and the other factors were significant contributors to the reported cost increases. Key Take-Away When project planning and coordination are taken to a higher level, it is possible to control nighttime construction costs and deliver quality work.
Cost 71 Tip Contractors equate risk to dollars. Therefore, to decrease the risk to contractors bidding on nighttime work and, consequently, decrease cost, agencies must be willing to have decision mak- ers available during all work hours; doing so may result in higher agency overhead cost, but much lower bid prices. Resources ⢠MDOTâRoad Cost Estimating Checklist http://www.michigan.gov/documents/ MDOT_0268_Road_Cost_Est_120543_7.pdf. ⢠MDOTâProject-Scoping Sheet http://www.michigan.gov/documents/MDOT_Project_ Scoping_120537_7.pdf.
