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Pavement Utility Cuts
2. Discussion of the Problem
This chapter of the manual describes the effects of excessive pavement utility cuts in the Nation's infrastructure. This discussion focuses on the degradation of the pavement and other public ROW infrastructure. In addition, this chapter considers the impacts on the public through user costs, traffic delay and business access, and the differences between state and local agencies in the methods of dealing with these impacts.
2.1 Degradation of National and Local Infrastructure
When utility companies, and others, make cuts into the pavement for utility installation or maintenance, not only does it affect the pavement structure itself, but also the other utilities which, with the pavement, are part of the national and local transportation infrastructure. This section includes a discussion on how utility cuts cause street pavements to deteriorate more quickly, and their potential effect on other utilities present in the highway and street system.
2.1.1 Untimely Pavement Deterioration
Utility cuts into the pavement of the Nation's highways and streets almost always increase the roughness of a pavement structure in both the immediate and surrounding areas of a cut. Not only do cuts increase pavement roughness, but they also introduce discontinuities in the pavement structure. Both of these can cause the pavement's expected life span to decrease. There are two types of degradation that can occur - structural and functional - both of which can cause early failure of the pavement, depending on the user's definition of pavement failure.
Structural Structural failure occurs when the pavement can no longer carry the loads for which it was designed without large deflections or deformations.(7)
Functional Functional failure occurs when the pavement no longer provides a smooth and safe riding surface for vehicles and passengers. A pavement can sometimes experience functional failure while remaining structurally sound. However, it is even less likely that a pavement that has experienced structural failure will remain functionally adequate.
Another aspect of pavement degradation is that a rough pavement can quickly lead to structural failure, through a synergistic effect. Rough pavements can cause vehicles to bounce, thus creating greater loads on the pavement, which can lead to more rapid advancement of structural failure, and by consequence, further functional failure, or roughness.
2.1.2 Congestion of Utilities
The chances of accidental rupture of existing underground utilities increase with increased congestion, or the density of utilities underground. This is not a problem solely associated with trenchless technology. Open trenching also poses a risk of disturbing existing utilities. In rural applications, the probability of encountering densely situated existing utilities is much lower. However, care should be taken to ensure any existing utilities are identified and located.
Public and private utilities are most often located in the public ROW, meaning that access to underground physical facilities often results in digging and backfilling trenches. Many times this means trenching into public roads: city streets, highways, and other public transportation facilities. While it is true that the utility companies' financial success depends on their ability to place facilities and provide services to customers as quickly as possible, the detrimental effects on the public transportation infrastructure has been largely overlooked in the past.
San Francisco, like many other cities in the Nation, confirmed its suspicion about the damage caused by utility street cuts after completing a study on the effects of cuts on the life of pavement.(2) The cities of Austin, Cincinnati, and Washington, DC, also conducted similar studies within the past six years.(4,5,1) These studies found that street cuts not only reduce the expected life of the streets but consequently cost millions of dollars to agencies in premature repair and street remediation expenses. Other financial impacts from utility cuts and poor repairs include traffic delays, increased congestion in urban areas and damage to both public and private vehicles.
2.2 Public Impacts
There are several types of impacts that excessive trenching and utility cuts can have on the public. These include those that cause a direct cost to the public in terms of money, and those that have indirect, or intangible, costs. Direct impacts are generally those that the public pays individually or collectively, whereas indirect impacts include those which are paid by society as a whole, and to which a specific price cannot be easily affixed.
2.2.1 Public Perception
In the public's perception, the highways and streets seem to be under construction constantly. If the road network is improved as a result of this construction, the public perception could become more positive. However, a poor perception is often the result, due to the endless presence of utility cuts and other road construction.
The public quickly notices when a newly-paved highway or street is cut for utility work. In the absence of a moratorium on cuts, or in an atmosphere of lenient enforcement of such a moratorium, pavement utility cuts can occur in new pavements quite frequently.
The ability to reduce the number of pavement utility cuts would have the obvious effect of reducing the number of work zones and pavement roughness. If an agency can encourage more utility work to be done using trenchless technology, the public is likely to notice. With the ability to control pavement utility cuts more closely, improved inspection could lead to better and more timely repairs, more coordination and sharing of information and resources between utility companies, and a better public perception of the agency and the infrastructure.
2.2.2 Traffic Delay
When a lane of traffic is temporarily made unavailable, and especially in areas of heavy traffic, vehicles can be delayed due to decreased traffic capacity.(8) If utility cuts are coordinated with joint trenching requirements, traffic delays can be minimized. Other impacts associated with traffic delay include costs to local businesses, user costs, air quality, and others. These will be discussed in the next sections.
2.2.3 Local Business
Lane closures and other traffic control associated with utility cuts can impact local business by either limiting access to the business, or by deterring potential customers from navigating around the traffic control. Especially in conditions of heavy traffic, motorists may choose to visit businesses in another location rather than spend additional time in traffic congestion caused by a utility cut work zone.
These costs are rarely quantifiable, but can result in significant impacts to local businesses. The importance of this impact is evident by the fact that most state and local transportation agencies require local business access mitigation for road construction or utility work.
2.2.4 User Costs
Direct impacts to users of a facility are often called user costs. These costs can include tangible items such as excess fuel, oil, maintenance, and time expended while negotiating a work zone, and the associated traffic congestion that often accompanies lane closures. Several studies have been conducted to quantify user costs in various situations and work zone configurations.(9,10,11)
Many of these user costs are also borne by the traveling public after the work zone has been removed, when a rough pavement remains. Studies have shown the relative incremental increase in user costs due to pavement roughness.(8,12,13)
2.2.5 Air Quality
While users of a highway or street facility accumulate costs due to the presence of a work zone, their excess fuel and oil consumed is creating additional vehicular emissions that contribute to the deterioration of the air quality. This effect is most pronounced in the immediate area of the work zone, but in urban areas, the excess emissions also contribute to the detriment of the overall air quality.(14,15)
2.2.6 Untimely Pavement Deterioration
The public pays the cost of untimely pavement deterioration either directly through premature maintenance and rehabilitation, or indirectly through the effect of rough roads on their vehicles. It is very difficult, if not impossible, to repair a pavement that has been cut to its original state. More appropriately, it is very difficult, if not impossible, to make a repair match the current state of the surrounding pavement's physical properties. Any other condition other than the pavement's current state can result in a rough surface to some degree. At the time of the repair, the pavement surface may be very smooth across the patched utility cut. However, after vehicles load the patch material for a time, differential material deformation is inevitable, of which roughness is a direct effect.(4)
While improved inspection and quality control on the part of the contractor can reduce the ultimate pavement roughness due to the cut, it is almost impossible to prevent it completely. Only a reduction in the number of utility cuts can preserve the pavement in its current, original state.