Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
F-1 A P P E N D I X F Example of Recommended Crash Reduction Program and Roadside Safety Treatments C. Paul Scott CRASH REDUCTION PROGRAM A concentration of crashes at a site or in a small area, or a certain type of crash that seems to occur over and over in a given jurisdiction, may indicate that the highway/utility system is contributing to crash potential. Utility pole crashes are subject to the same types of crash patterns as other types of roadway crashes. They are thus subject to traditional highway crash study procedures. Detailed study of crash records may identify high-crash locations and point out improvements that will reduce the number and severity of future crashes. Road users can also provide input into the nature and causes of highway/utility crashes. The following steps are normally included in a comprehensive crash-reduction program: â¢ Setting up a traffic records system, â¢ Identifying high-crash locations, â¢ Analyzing high-crash locations, â¢ Correcting high-crash locations, and â¢ Reviewing the results of the program. The size of the organization conducting the program has a great deal to do with its sophistication and complexity. Small highway agencies or utility companies may find it sufficient to place pins on a city map to identify high-crash locations and then review copies of police accident reports to select the best safety treatment. Large utility companies, units of local government, and highway agencies may resort to computers to handle enormous volumes of data. Crash reduction programs at this level frequently use sophisticated statistical software to select the best sites for treatment and to identify the most appropriate countermeasures. SETTING UP THE TRAFFIC RECORD SYSTEM The first step is to gain access to crash data containing utility-specific information. Local government units and utility companies may need to visit the local law enforcement agency to discuss their proposed crash reduction programs and the types of data they will need to identify sites for further study. Once law enforcement officers are aware of the need to collect data on the number and types of utility devices involved in collisions,
F-2 Utility Pole Safety and Hazard Evaluation Approaches At the same time the crash data are being gathered, it may be appropriate to gather information on traffic volumes, speed limits (regulatory and advisory), roadway configurations, roadway and shoulder conditions, street or pavement widths, shoulder widths, right-of-way widths, pavement slopes and superelevation, distances of poles from the edge of pavement, locations of adjacent structures or trees, and other geometric data for sites where crashes have involved utility facilities. IDENTIFYING HIGH-CRASH LOCATIONS A high-crash location is a site that has more crashes than similar sites with similar traffic volumes. There is never enough money to fix every site where crashes occur, so it is prudent to concentrate available funds on those sites most deserving of treatment. There are at least five ways to identify high-crash sites: 1. Number method: This is the simplest method. The number of crashes occurring at each site is identified, and the sites with the highest numbers become candidates for treatment. There is a critical weakness with this method. Sites with higher traffic volumes have a higher number of crashes. It may be normal for an intersection used by 50,000 cars a day to have 20 crashes in a year. However, it would be unusual for an intersection used by 200 cars a day to have the same number of crashes. This latter case might indicate a crash problem. 2. Rate method: This method overcomes the weakness of the number method by taking into account the number of vehicles passing each site. Crash rates are calculated and expressed as the number of crashes per million vehicles entering an intersection or per hundred million vehicle miles driven along a section of roadway. This method also has a crucial weakness. For very low-volume roadways, a single crash may produce a very high crash rate, which would be misleading. 3. Numberârate method: The user calculates the number of crashes and the crash rate. A site with high values in both categories is considered for further investigation. This overcomes the individual weaknesses of the number and the rate methods. 4. Rateâquality control method: This procedure uses statistical tests to determine whether the number of crashes, or the crash rate, at a specific site is above the systemwide average for similar sites. 5. Crash severity method: This method applies when sites are being evaluated. Several state transportation departments have incorporated this procedure. Each injury crash could be equivalent to x property-damage-only (PDO) crashes, and each fatal crash could be equivalent to y injury crashes. Thus, all the injury and fatality crashes at a site could be converted to the equivalent number of PDO crashes. Sites with severe injury and fatality patterns would have large conversions and would rank higher on the priority list. the availability of such data usually improves. Utilities may find it useful to compile their own files of crash information based on maintenance records of repair to damaged poles, observations of employees, or citizen input. For small utilities and small local governments, it may be sufficient to tabulate the crash information and to identify crashes on local street maps.
Example of Recommended Crash Reduction Program and Roadside Safety Treatments F-3 crashes, the number procedure may suffice. For statewide studies, the rateâquality control feature may be best. In each instance, the method chosen should determine whether the number of high-crash experiences is above desired limits and where analysis and safety treatments will do the most good for the public. ANALYZING HIGH-CRASH LOCATIONS A site may be selected for further study because of the number, rate, or severity of utility pole collisions, or because it fits a pattern of sites that have been designated for systemwide improvements. After a site has been identified for further analysis, the analyst begins looking for patterns of crash types and causes. Once the pattern has been identified, appropriate treatments can be selected. The following steps are found in a typical site analysis: 1. Prepare a collision diagram (i.e., a sketch that uses arrows to show the types of collisions that are occurring). Such sketches may indicate poles too close to the roadway, poles that are hard for drivers to see, turning maneuvers that are too difficult for drivers to master, and similar factors that contribute to crashes. 2. Prepare a condition diagram (i.e., a scale drawing that shows the roadway geometry and any features that might have contributed to the crash). Typically, this diagram includes utility facilities, traffic control devices, street widths, intersection geometry, roadway grade or superelevation that may encourage vehicles to leave the traveled way when wet, and similar features. 3. Tabulate available data and look for patterns. Police accident reports can be used to tabulate type of fixed object (e.g., pole or tree), crash severity, day of week, time of day, weather conditions, and similar factors. Tabulating the time of day and pavement condition, for example, may reveal that most crashes happen at night. This pattern may be a clue that the utility poles are hard to see. 4. Visit the site. The analyst can visit the site to relate the findings from collision diagrams, condition diagrams, and tabulations. The observer may find poles too close to the road, poles on the outside of a curve, turning radii that are too sharp, high-speed traffic, and other characteristics that contribute to the crash pattern. Sometimes these steps will identify a dominant crash pattern at a site, but often it is not so simple. There may be several crash patterns. Once the pattern or patterns are determined, it is usually possible to diagnose the cause of these patterns and to develop appropriate treatments. CORRECTING HIGH-CRASH LOCATIONS For each high-crash location, several appropriate safety treatments may be available. Each alternative improvement is evaluated to determine its cost-effectiveness. This involves estimating the number of crashes that will be prevented by a certain treatment and then The best procedure for a particular study depends largely on the size of the area being studied and the number of crashes that have occurred. For very small locations with few
F-4 Utility Pole Safety and Hazard Evaluation Approaches assigning cost savings due to decreased crash costs. Agencies such as the National Safety Council and the National Highway Traffic Safety Administration periodically publish estimates of crash costs. The cost savings are compared with the cost of installing and maintaining the improvement to generate a cost-effectiveness for the treatment. Once all the alternatives have been evaluated, the most cost-effective treatment is selected. For a study of a large system, sophisticated computer programs may be used to identify the best sites and the most appropriate treatment at each site. The final step in selecting treatments is to set priorities. Treat those sites first that would do the most good for the public (i.e., prevent the most crashes, injuries, and fatalities). Highway agencies and utility companies are sometimes reluctant to identify sites that need safety treatment or to set priorities for treatment because of perceived liability. They may be afraid a list of high-crash sites could be used in court to show they were aware of crash problems but not concerned enough to do something about them. Federal legislation has been adopted to help alleviate this problem. Title 23, United States Code, Section 409 (23 U.S.C. 409), prevents the âdiscoveryâ or admittance into evidence of most kinds of information gathered or used to identify sites as part of a safety program that utilizes federal-aid highway funds. The intent is to encourage safety programs by shielding the transportation department or utility company from spurious suits. REVIEWING THE CRASH REDUCTION PROGRAM An important part of a crash reduction program is to determine whether previous treatments have worked. This involves periodic review of the sites after the treatments have been installed to make sure they have functioned as intended. Crash data may be collected to determine whether the number and severity of collisions have been reduced. A before-and-after study may be undertaken to make this determination. Many publications are available to provide more complete information to guide highway agencies and utility companies interested in implementing crash reduction programs. Each state transportation department has a highway safety office or a traffic operations office that can help organize the program and provide pertinent publications, supply crash data, and otherwise contribute to a highway/utility crash reduction program. ROADSIDE SAFETY TREATMENTS Ideally, the clear zone should be free of obstacles [clear zone is defined in the AASHTO Roadside Design Guide (1) as the total roadside border area, starting at the edge of the traveled way and extending a variable distance depending on traffic volumes, speeds, and roadway geometry]. Where these obstacles must be placed in the clear zone, or where an analysis has shown that an existing obstacle may need treatment, many options are available. The following list generally has been considered as the desirable order of treatment: â¢ Remove the obstacle. â¢ Relocate the obstacle where it is less likely to be struck.
Example of Recommended Crash Reduction Program and Roadside Safety Treatments F-5 â¢ Reduce the number of poles. â¢ Reduce impact severity by using an appropriate breakaway device. â¢ Redirect a vehicle by shielding the obstacle with a longitudinal traffic barrier or crash cushion. â¢ Warn of the presence of the obstacle if the preceding alternatives are not appropriate. These are general treatments, and many variations and combinations may be used. Researchers have identified the factors that contribute most substantially to crashes along utility pole lines. The most prevalent of these appear to be lateral clearance to the pole, volume of traffic, and pole density per mile. Lists of countermeasures have been developed to address these factors in utility pole crash problems. KEEP THE VEHICLE ON THE ROADWAY One obvious way to prevent utility pole crashes is to assist the driver in staying on the roadway. This may be done by positive guidanceâfor example, using pavement markings, delineators, advance warning signs, and other visual cues to tell the driver what to expect and to provide a visual path through a site. Physical enhancements such as improving the skid resistance of the pavement, widening the pavement travel lanes, widening or paving shoulders, improving the superelevation, straightening sharp curves, decreasing the speed of vehicles, and adding lighting in areas where crashes frequently occur at night may also diminish crash potential by decreasing the number of vehicles that for whatever reason leave the travelway. UNDERGROUND UTILITY LINES By burying utility lines, poles can be removed, greatly reducing crash potential. This alternative saves the utility company the costs of removing and replacing a pole damaged in a collision and of repairing the utility line after a crash. The primary disadvantage of this treatment is the additional initial expense. In addition, the line is now vulnerable to excavation damage, an additional connection may be necessary to provide reliable service, and the line is more difficult to patrol in the case of an outage. Even with underground utility lines, there still may be a need to safety treat ground surface pad-mounted transformers, switch cabinets, pedestals, and other associated hardware. When these devices are installed, they should conform to the applicable clear zone guidelines. Underground installations are not the only acceptable treatment, and other types may be preferred for some sites. Rock formations, marsh, and similar site conditions may make underground treatment too expensive. It also may be difficult to handle unanticipated local growth, or it may be impossible to tap some underground facilities to add customers. In spite of these and other difficulties, an underground installation may be the best design solution. In some jurisdictions the utility may collect the incremental cost of placing an underground facility, particularly where overhead facilities are the basis for rates.
F-6 Utility Pole Safety and Hazard Evaluation Approaches INCREASED LATERAL OFFSET Both crash rate and crash severity will decrease when utility poles are moved farther from the travelway. Ideally, the poles can be placed at the right-of-way line and outside the clear zone. Vertical construction can sometimes be used instead of cross-arm construction to provide more lateral clearance. The full effectiveness of moving poles away from the roadway cannot be achieved if other fixed objects are allowed to remain in the clear zone. A utility pole crash reduction program should be part of a comprehensive plan that removes all types of objects from the clear recovery area. LOCATIONS LESS LIKELY TO BE STRUCK There are many fewer off-road crashes on the inside of horizontal curves than on the outside. Consideration should be given to placing pole lines on the inside of curves. On winding roads, this placement may not be feasible, because the wires would have to cross the road each time sequential curves changed directions. For sharp curves, utility poles would need lateral bracing from compression struts or guy wires. With limited right-of-way, this might not be possible. Some state policies prohibit anchor guys between poles and the traveled way. Some jurisdictions prohibit compression struts. The alternatives include expensive self-supporting poles or anchor guys that extend into adjacent property if feasible and if permission can be obtained. Where retaining walls, guardrails, non-traversable ditches, and similar features exist, pole lines can be placed behind them. Errant vehicles cannot travel past them to strike the poles. REDUCED NUMBER OF UTILITY POLES An obvious way to decrease utility pole crashes is to decrease the number of poles beside the roadway. There are several methods available. â¢ Encourage joint use of existing poles, with one pole carrying streetlights, electric power, telephone, cable television, and other utility lines. â¢ Place poles on only one side of the street. â¢ Increase pole spacing by using bigger, taller poles. â¢ Selectively move poles away from hazardous locations. Before any of these procedures is adopted, an engineering study should be conducted to determine whether the changes would be cost-effective and appropriate for the specific site. For example, increasing the spacing of poles requires that the remaining poles be larger and taller than the previous ones. These larger poles will be struck less frequently because there are fewer of them. However, the severity of the crashes may be greater because of their larger size and thus cancel any savings that might have accrued because of the decreased number of crashes.
Example of Recommended Crash Reduction Program and Roadside Safety Treatments F-7 Also, using bigger, taller poles is not a simple solution. In most cases, pole spacing is dictated by conductor size and characteristics and by codes and conductor spacing/clearance requirements. Some rules require that poles be placed at lateral property lines. Ideal span lengths for power poles may be too great for communication conductors. Typically joint-use spans are shorter than power line spans. Removing or relocating a few poles in areas of high hazard may be used as a treatment after several crashes have occurred. This countermeasure requires no formal economic analysis and may be particularly appropriate in rural areas. BREAKAWAY DEVICES When a pole must remain in place, it can be modified to break away upon impact and swing out of the path of the vehicle, reducing the severity of the crash. Breakaway sign supports and breakaway luminaire supports have been used for many years. Breakaway timber utility poles have been made available through research conducted for the Insurance Institute for Highway Safety in the 1970s and for FHWA in the early 1980s. Breakaway utility poles cannot be used at every location, but there are instances and circumstances for which they may be the most appropriate crash reduction treatment. Guy wires for utility poles can also cause crashes. They snag and flip vehicles that strike them and can cause severe injuries to cyclists. Guy wires that are closer to the traveled way than the structure they support should be avoided. Research is being conducted to develop a breakaway guy wire coupling. ROADSIDE BARRIERS AND CRASH CUSHIONS If it is not feasible or practical to remove utility structures, move them, or place them underground, then other treatments may be necessary. One type of acceptable treatment is to shield the vehicle from striking the fixed object. Roadside barriers perform this function by redirecting the vehicle away from the utility structure, allowing the driver an opportunity to recover control of the vehicle. The AASHTO Roadside Design Guide (1) may be used to determine whether a roadside barrier is an appropriate treatment and, if so, what design is suitable for site conditions. A roadside barrier is a longitudinal system used to shield motorists from natural or man-made hazards located along either side of a roadway. There are instances in which a roadside barrier is not appropriate. One example involves flexible and semirigid barrier systems when there is not enough room between the barrier and the fixed object for the barrier to fully deflect during impact. Also, a roadside barrier should be placed as far from the traveled way as conditions permit. Other helpful design information can be found in the Roadside Design Guide (1).
F-8 Utility Pole Safety and Hazard Evaluation Approaches Another way to shield a vehicle from striking a utility pole is to use a crash cushion, which functions by collapsing upon impact and slowing the vehicle at a controlled rate. A crash cushion is normally used where there is an isolated fixed object hazard. If there are several objects, a roadside barrier is probably a better safety device. Crash cushions typically are much more expensive than roadside barriers. Crash cushion design is more complex than barrier design. The type of crash cushion and its dimensions must be designed to fit site conditions and to absorb energy (from the impacting vehicle) at the appropriate rate. The Roadside Design Guide (1) is the source of information for the design process. Roadside barriers and crash cushions should not be used indiscriminately for at least two reasons: they are expensive to install and to maintain, and they are closer to the road than the objects they are shielding. They are involved in more crashes than unshielded objects. They should be used only when they are warranted to reduce crash severity. WARNING THE MOTORIST OF THE OBSTACLE The number of crashes or the severity of crashes may be decreased by warning motorists of the presence of poles adjacent to the roadway. This may be done with warning signs, reflective paint, sheeting, object markers placed on utility poles, and roadway lighting. Poles on the outside of a horizontal curve, where a lane becomes narrow, at the end of a lane drop, and in other locations where vehicles are likely to travel close to them are candidates for such warning where more comprehensive treatments are not justified. SELECTING COUNTERMEASURES The method used for selecting countermeasures depends on the size and complexity of the project. For an individual site, the selection may be made through the judgment of an informed individual or a group of individuals. For a systemwide project or for a series of sites, the decision may be based on a costâbenefit analysis or a sophisticated, computer- aided optimization procedure. There is also a methodology specifically designed by FHWA for utility pole treatment determinations. DIAGNOSTIC REVIEW TEAM The experience of several agencies and the knowledge of informed parties may be brought together to review a crash problem at a particular site. State transportation departments do this routinely as part of the Federal-Aid Highway Safety Improvement Program. Once a site has been identified for investigation and possible treatment, a diagnostic review team is appointed. The composition of the team is matched to the particular problem. For utility poles, FHWA encourages state, utility company, and FHWA representatives to work together to identify hazardous sites and evaluate the various countermeasures being considered. Utility staff members should be invited to join field reviews. They may be able to supply information about the planned upgrading of the utility line, replacement options, and alternative designs that would assist in making a decision about the most appropriate countermeasures.
Example of Recommended Crash Reduction Program and Roadside Safety Treatments F-9 Whenever possible, utility corrective work should be handled in conjunction with highway or utility upgrading and during utility rehabilitation projects to minimize the overall cost of the program. Typical results of a field review are a series of recommendations for potential treatments. For small projects, there may be only one or two recommendations. For large projects, the recommendations may be complex and require further analysis. COST-EFFECTIVENESS STUDY The second procedure for selecting countermeasures is to perform a cost-effectiveness analysis. This involves comparing the costs of various treatments to determine the most effective use of limited funding. Costs include items such as potential future crashes, initial construction costs, ongoing maintenance, and similar items. Benefits include a reduction in the number of crashes with a commensurate savings of crash costs, reduced maintenance costs, possible savings in travel time for motorists, and the salvage value of the facility at the end of the useful service life. The time value of money is considered by applying the net present worth procedure (or a similar method) to the costs and benefits. Benefits and costs are compared to determine whether an improvement is cost-effective and to set priorities among the many projects competing for limited highway funds for safety improvements. The appendix of the Roadside Design Guide (1) contains a good cost-effectiveness methodology. Example calculations are provided to illustrate the methodology. This procedure has also been adapted to the computer. Instructions about ordering the software for the cost-effectiveness procedure may be found in the Roadside Design Guide (1). For large projects or for a statewide crash reduction program, comprehensive computer programs perform many of the calculations. They also may use advanced statistical techniques to optimize funding and to produce master lists of acceptable projects. UTILITY POLE COST-EFFECTIVENESS PROCEDURE Zegeer and Parker (2) developed a cost-effectiveness procedure specifically for selecting utility pole countermeasures. This methodology was published as an FHWA report, which is full of tables, graphs, and charts that can predict the number of traffic crashes involving utility poles of different configurations. Once an agency has decided to undertake a treatment program, it can use this methodology to test alternative designs to see which yields the most cost-effective treatment. This procedure normally requires a field inspection program to gather the data necessary to perform the methodology. The FHWA report provides data sheets for this purpose, along with step-by-step instructions for performing the field inventory. A research project conducted for FHWA developed a computerized version of the utility pole cost-effectiveness model. This program was called UPACE. It performs the
F-10 Utility Pole Safety and Hazard Evaluation Approaches drudgery of calculating the anticipated number of crashes; making adjustments for the various types of crashes in the clear zone; and estimating the expected cost of treatment, expected total reduction in crashes, expected cost savings, and other predictions needed to evaluate the effect of the treatment. The software is now marketed by the McTrans Center in the Civil Engineering Department at the University of Florida. BEST METHOD There is no such thing as a method that is always the best. The best method for selecting countermeasures depends on local conditions, size of the program, funds available, and other factors. REFERENCES 1. Roadside Design Guide. AASHTO, Washington, D.C., 1996. 2. Zegeer, C. V., and M. R. Parker, Jr. Cost-Effectiveness of Countermeasures for Utility Pole Accidents. FHWA Report FHWA/RD-83/063 8009/8209; HS-037 308, FHWA, 1985.