Final Report for Research Project HR-181, Macadam Base Shoulders, September 1981

Highway safety and pavement performance can be directly influenced by the type of shoulders that are constructed. Shoulder design alternatives have always been rather limited. Moreover, the use of some of the alternatives has always been restricted by funding limitations. This research project seeks to explore the use of modified macadam base construction for shoulders. This type of shoulder design could offer the designer another option when paved or stabilized shoulders are being considered. Macadam base construction has in the past been shown to be quite strong and free draining. Two macadam base shoulder designs were developed and constructed for this research project. A new roadway embankment and P.C.C. pavement were constructed on a section of US 6 east of Adel in Dallas County. The macadam base shoulders were constructed adjacent to the pavement as part of the project. The north shoulder was finished with a choke stone course and bituminous surface treatment and the south shoulder was finished with a two (2) inch layer of Type B Class I1 asphalt concrete. Macadam stone base shoulders can be built with relatively minor construction problems with comparable strength and less cost than asphalt treated base shoulders. The macadam stone base shoulders have performed well with very little maintenance necessary. The improved drainage substantially reduces deterioration of the pavement joints.

Safer Constrauction and Maintenance Practices to Minimize Potential Liabiliy by Counties from Accidents, Septemeber 1979

Tort claims resulting from alleged highway defects have introduced an additional element in the planning, design, construction, and maintenance of highways. A survey of county governments in Iowa was undertaken in order to quantify the magnitude and determine the nature of this problem. This survey included the use of mailed questionnaires and personal interviews with County Engineers. Highway-related claims filed against counties in Iowa amounted to about $52,000,000 during the period 1973 through 1978. Over $30,000,000 in claims was pending at the end of 1978. Settlements of judgments were made at a cost of 12.2% of the amount claimed for those claims that had been disposed of, not including costs for handling claims, attorney fees, or court costs. There was no clear time trend in the amount of claims for the six-year period surveyed, although the anount claimed in 1978 was about double the average for the preceding five years. Problems that resulted in claims for damages from counties have generally related to alleged omissions in the use of traffic control devices or defects, often temporary, resulting from alleged inadequacies in highway maintenance. The absence of stop signs or warning signs often has been the central issue in a highway-related tort claim. Maintenance problems most frequently alleged have included inadequate shoulders, surface roughness, ice o? snow conditions, and loose gravel. The variation in the occurrence of tort claims among 85 counties in Iowa could not be related to any of the explanatory variables that were tested. Claims hppeared to have occurred randomly. However, using data from a subsample of 11 counties, a significant relationship was shown probably to exist between the amount of tort claims and the extensiveness of use of wcirning signs on the respective county road systems. Although there was no indication in any county that their use of warning signs did not conform with provisions of the Manual on Uniform Traffic Control Devices (Federal Highway Administration, Government Printing Office, Washington, D.C., 1978), many more warning signs were used in some counties than would be required to satisfy this minimum requirement. Sign vandalism reportedly is a problem in all counties. The threat of vandalism and the added costs incurred thereby have tended to inhibit more extensive use of traffic control devices. It also should be noted that there is no indication from this research of a correlation between the intensiveness of sign usage and highway safety. All highway maintenance activities introduce some extraordinary hazard for motorists. Generally effective methodologies have evolved for use on county road systems for routine maintenance activities, procedures that tend to reduce the hazard to practical and reasonably acceptable levels. Blading of loose-surfaced roads is an examples such a routine maintenance activity. Alternative patterns for blading that were investigated as part of this research offered no improvements in safety when compared with the method in current use and introduced a significant additional cost that was unacceptable, given the existing limitations in resources available for county roads.

Signing on Very Low Volume Rurd Roads Iowa DOT Project HR-262, July, 1984

Research was undertaken to define an appropriate level of use of traffic control devices on rural secondary roads that carry very low traffic volumes. The goal of this research was to improve the safety and efficiency of travel on the rural secondary road system. This goal was to be accomplished by providing County Engineers with guidance concerning the cost-effective use of traffic control devices on very low volume rural roads. A further objective was to define the range of traffic volumes on the roads for which the recommendations would be appropriate. Little previous research has been directed toward roads that carry very low traffic volumes. Consequently, the factual input for this research was developed by conducting an inventory of the signs and markings actually in use on 2,069 miles of rural road in Iowa. Most of these roads carried 15 or fewer vehicles per day. Additional input was provided by a survey of the opinions of County Engineers and Supervisors in Iowa. Data from both the inventory and the opinion survey indicated a considerable lack of uniformity in the application of signs on very low volume rural roads. The number of warning signs installed varied from 0.24 per mile to 3.85 per mile in the 21 counties in which the inventory was carried out. The use of specific signs not only varied quite widely among counties but also indicated a lack of uniform application within counties. County officials generally favored varying the elaborateness of signing depending upon the type of surface and the volume of traffic on different roads. Less elaborate signing would be installed on an unpaved road than on a paved road. A concensus opinion was that roads carrying fewer than 25 vehicles per day should have fewer signs than roads carrying higher volumes. Although roads carrying 0 to 24 vehicles per day constituted over 24% of the total rural secondary system, they carried less than 3% of the total travel on that system. Virtually all of these roads are classified as area service roads and would thus be expected to carry only short trips primarily by local motorists. Consequently, it was concluded that the need for warning signs rarely can be demonstrated on unpaved rural roads with traffic volumes of fewer than 25 vehicles per day. It is recommended that each county designate a portion of its roads as an Area Service Level B system. All road segments with very low traffic volumes should be considered for inclusion in this system. Roads included in this system may receive a lesser level of maintenance and a reduced level of signing. The county is also afforded protection from liability arising from accidents occurring on roads designated as part of an Area Service Level B system. A uniform absence of warning signs on roads of this nature is not expected to have any discernible effect on the safety or quality of service on these very low volume roads. The resources conserved may be expended more effectively to upgrade maintenance and traffic control on roads carrying higher volumes where the beneficial effect on highway safety and service will be much more consequential.

Use of Incentive/Disincentive Contracting to Mitigate Work Zone Traffic Impacts, 2012

Incentive/disincentive clauses (I/D) are designed to award payments to contractors if they complete work ahead of schedule and to deduct payments if they exceed the completion time. A previously unanswered question is, “Did the costs of the actual work zone impacts that were avoided justify the incentives paid?” This report answers that question affirmatively based on an evaluation of 20 I/D projects in Missouri from 2008 to 2011. Road user costs (RUC) were used to quantify work zone impacts and included travel delays, vehicle operating costs, and crash costs. These were computed using work zone traffic conditions for partial-closure projects and detour volumes and routes for full-closure projects. Conditions during construction were compared to after construction. Crash costs were computed using Highway Safety Manual methodology. Safety Performance Functions produced annual crash frequencies that were translated into crash cost savings. In considering an average project, the percentage of RUC savings was around 13% of the total contract amount, or $444,389 of $3,464,620. The net RUC savings produced was around $7.2 million after subtracting the approximately $1.7 million paid in incentives. In other words, for every dollar paid in incentives, approximately 5.3 dollars of RUC savings resulted. I/D provisions were very successful in saving RUC for projects with full-closure, projects in urban areas, and emergency projects. Rural, non-emergency projects successfully saved RUC but not at the same level as other projects. The I/D contracts were also compared to all Missouri Department of Transportation contracts for the same time period. The results show that I/D projects had a higher on-time completion percentage and a higher number of bids per call than average projects. But I/D projects resulted in 4.52% higher deviation from programmed costs and possibly more changes made after the award. A survey of state transportation departments and contractors showed that both agreed to the same issues that affect the success of I/D contracts. Legal analysis suggests that liquidated damages is preferred to disincentives, since enforceability of disincentives may be an issue. Overall, in terms of work zone impact mitigation, I/D contracts are very effective at a relatively low cost.

Roadway Lighting on Secondary Roads in Iowa, HR-251, 1984

There are approximately 800 installations of destination lighting at secondary road intersections in Iowa. Approximately 90% of these have only a single luminaire. The other installations have two luminaires. No warrants currently exist for justifying the use of this type of lighting. Previous research has examined the safety benefits from full lighting of rural intersections that generally serve substantially higher traffic volumes than secondary road intersections in Iowa. However, the safety benefit of destination lighting at intersections carrying relatively low volumes has not been the subject of previous research. The research reported here, sponsored by the Iowa Department of Transportation, was undertaken to identify locations where destination lighting could be expected to improve highway safety. If destination lighting were shown to reduce accident frequency, warrants for its use on secondary roads could be developed. An inventory of secondary road lighting installations in Iowa was assembled. From this inventory, two samples were constituted that would permit two separate comparisons of the accident experience with and without destination lighting. Before and after comparisons were made for the same locations if accident records were available for at least one full year both preceding and following the installation of destination lighting. Accident records for this purpose were available from a statewide computerized record system covering the period from 1977 through 1982. The accident experience at locations having destination lighting installed before 1978 was compared with a sample of comparable locations not having destination lighting. The sample of secondary road intersections used for the before and after comparison included 91 locations. The sample of continuously lighted locations included 102 intersections. Accident experience at these locations was compared with the experience at 102 intersections that were not lighted. The intersections included in these samples averaged only 0.31 accidents per year. The accident rate at secondary road intersections that had destination lighting did not differ significantly from the accident rate at intersections that were not lighted. This conclusion was derived from both comparisons, the before and after experience and the comparison of experience at intersections that were continuously lighted with that at unlighted locations. Furthermore, no significant differences were noted between lighted and unlighted locations in the proportion of accidents that occurred at night. The distribution of accidents by type also did not differ between unlighted intersections and those having destination lighting. It was not possible to formulate warrants for destination lighting since analyses directed toward identifying specific characteristics of an intersection that could be correlated with highway safety did not yield any useful relationships. However, it was noted that the average damages for night accidents that occurred at lighted intersections were lower than for accidents at unlighted intersections. Even in the absence of a more definitive demonstration of beneficial effects, destination lighting is perceived by officials in most of the counties having such installations as yielding desirable effects and is recognized as helpful to motorists in performing the guidance function in driving. Given this benefit and a relatively low cost (an average of $74 per year for one luminaire), and given that the subjective criteria that have been used in the past to justify the installation of destination lighting have led to a high degree of public acceptance and satisfaction, it is recommended that the same subjective criteria continue to be used in lieu of definitive warrants.

Engineering Study Automating Iowa's Speed Monitoring Program, HR-228, 1983

Excessive speed on State and County highways is recognized as a serious problem by many Iowans. Speed increases both the risk and severity of accidents. Studies conducted by the FHWA and NHTSA have concluded that if average speeds were increased by five MPH, fatalities would increase by at least 2,200 annually. Along with the safety problems associated with excessive speed are important energy considerations. When the national speed limit was lowered to 55 MPH in 1974, a tremendous savings in fuel was realized. The estimated actual savings for automobiles amounted to 2.2 billion gallons, an average of 20.75 gallons for each of the 106 million automobiles registered in 1975. These benefits prompted the Federal-Aid Amendment of 1974 requiring annual State enforcement certification as a prerequisite for approval of Federal-aid highway projects. In 1978, the United States D.O.T. recommended to Congress significant changes in speed limit legislation designed to increase compliance with the national speed limit. The Highway Safety Act of 1978 provides for both withholding Federal-aid highway funds and awarding incentive grants based on speed compliance data submitted annually. The objective of this study was to develop and make operational, an automatic speed monitoring system which would have flexible capabilities of collecting accurate speed data on all road systems in Iowa. It was concluded that the Automatic Speed Monitoring Program in Iowa has been successful and needed data is being collected in the most economical manner possible.

Macadam Base Shoulders, HR-181, 1977

Highway safety and pavement performance can be directly influenced by the type of shoulders that are constructed. Shoulder design alternatives have always been rather limited. Moreover, the use of some of the alternatives has always been restricted by funding limitations. This research project seeks to explore the use of modified macadam base construction for shoulders. This type of shoulder design could offer the designer another option when paved or stabilized shoulders are being considered. Macadam base construction has in the past been shown to be quite strong and freedraining. Two macadam base shoulder designs were developed and constructed for this research project. A new roadway embankment and P.C.C. pavement were constructed on a section of US 6 east of Adel in Dallas County. The macadam base shoulders were constructed adjacent to the pavement as part of the project. The north shoulder was finished with a choke stone course and bituminous surface treatment and the south shoulder was finished with a two (2) inch layer of Type B Class II asphalt concrete. The initial results are considered satisfactory. Follow-up performance evaluation and load bearing tests are planned.

Sprinkle Treatment of Asphalt Surfaces, HR-199, 1984

Methods of improving highway safety are of major concern to everyone who is involved in the planning, development and construction of improvements of our vast highway network. Other major concerns are the conservation of our rapidly disappearing sources of energy and quality building materials. This research is devoted to further exploration of a process which will: 1. help preserve higher quality aggregates; and, 2. improve the frictional characteristics and surface texture of asphalt pavement surfaces. Sprinkle treatment of asphalt concrete pavement surfaces with a non-polishing aggregate, a procedure which was developed in Europe, is one method which has shown promise in accomplishing the above listed objectives. This research seeks to explore the feasibility and cost effectiveness of using standard asphalt mixtures of local, less expensive aggregates for surface courses followed by a surface sprinkle treatment of a hard, durable, non-polishing layer of precoated chips to produce a durable, non-skid pavement surface for safe highway travel. Three standard mixture types are being evaluated for aggregate retention characteristics and six sprinkle aggregates are being evaluated for durability, polishing and friction characteristics. In addition, measurements of the surface texture by the silicone putty method are being made. Another feature of this research is the evaluation of a rubberized asphalt material called Overflex MS as a crack filler. It has been reported that the material could be beneficial in reducing reflective cracking. The project was begun in July of 1978 and was completed in August. A review made in the spring of 1979 indicates very satisfactory performance. It was determined from slide photos taken after construction and again in the spring that aggregate retention was very good. However, many cracks had reflected indicating that the Overflex MS had not been effective. Follow up friction test results and texture analysis were also very good. The results of these tests are shown in Appendix A.

Warrants for Rumble Strips on Rural Highways, HR-235, 1982

Research was undertaken, sponsored by the Iowa Department of Transportation, to identify specific locations where rumble strips could be expected to improve highway safety. The objective of the research was to recommend warrants for their use on rural highways. An inventory of rumble strip installations on the rural highway systems in the state was conducted in 1981. A total of 685 installations was reported on secondary roads and 147 on primary highways. Over 97 percent of these were in advance of stop signs at. intersections. Most of the other installations were in advance of railroad grade crossings. The accident experience with and without rumble strips was compared in two ways. A before-and-after comparison was made for the same location if accident records were available for at least one full year both preceding and following the installation of rumble strips. Accident records for this purpose were available from a statewide computerized record system covering the period from 1977 through 1980. The accident experience at locations having rumble strips installed before 1978 was compared with a sample of comparable locations not having rumble strips.

Evaluation of a Mobile Rut Depth Device for the Pavement Management Program, HR-248, 1984

With inflation, there is no longer a completely adequate budget for highway construction and maintenance. Restricted budgets have generated development and implementation of pavement management programs. A need for management guidelines generated National Cooperative Highway Research Program Synthesis of Highway Practice 84, "Evaluation Criteria and Priority Setting for State Highway Programs". Traffic volumes and present conditions are two major factors in determining the priority of a proposed highway improvement. The Iowa DOT, Highway Division, Office of Materials has been conducting pavement condition inventory surveys on a three-year frequency since 1969 as input for pavement management. Development of substantial wheel rutting on paved roadways results in a potential hazard to highway safety. During periods of rain, these water-filled ruts may cause hydroplaning and loss of vehicle control. It is, therefore, imparitive that Iowa roadways be continually monitored for rut depths and further that this data be used in a pavement management program to determine priorities for rehabilitation or resurfacing.

Training Aids to Reduce Potential County Liability, HR-289, Draft, 1987

Iowans who travel secondary roads regard these roads as a very important part of their lives. These highways provide a means of transporting products to market and children to school. They are also links to nearby cities and towns. Nearly 3.8 billion vehicle miles of travel occur each year on Iowa's nearly 90,000 mile secondary road system. Accidents do happen. However, improvements in highways, in vehicles, in driver education, in legislation, and in enforcement have combined to make driving in Iowa very safe. If our highways are to remain safe, these efforts need to be continued. This presentation was developed to help county highway department personnel in their effort to maintain and improve highway safety. The presentation is not a standard, specification or regulation.

Sprinkle Treatments for Asphalt Concrete, HR-507, 1986

In recent years, the Iowa Department of Transportation has put greater emphasis on improving highway safety. This effort has been relatively successful with a reduction in traffic-related fatalities to levels experienced prior to 1950. The nationwide speed limit of 55 mph was probably the greatest contributor to the decline in traffic fatalities, but there have been many other efforts that have also contributed to this decline. The Iowa DOT has been testing all paved roadways periodically for friction coefficient since 1969. New techniques have been used to obtain a greater depth of surface texture on paved roadways. Transverse tined grooving has been used on portland cement concrete to provide increased texture depth.

Performance Measures for Iowa Transportation Systems, 2006

The purpose of performance measures in planning operations is to identify and track meaningful, quantifiable measures that reflect progress toward the goals of the plan. The Iowa Department of Transportation (DOT) has already adopted performance measures in a number of operational areas, including highway maintenance, highway safety, public transportation, and aeronautics. This report is an initial effort to utilize performance measures for transportation system planning. The selected measures provide a cross-section of system performance indicators across three selected transportation planning goals (safety, efficiency, and quality of life) and five transportation modes (highways/bridges, public transit, railroads, aviation, and pedestrian/bicycle). These performance measures are exploratory in nature, and constitute a first attempt to apply performance measures in the context of a statewide, multimodal transportation plan from the Iowa DOT. As such, the set of performance measures that the Iowa DOT uses for planning will change over time as more is learned about the application of such measures. The performance measures explained in this document were developed through consultation with Iowa DOT modal staff (aviation, railroads, highways, public transportation, and pedestrian/bicycle) and the Office of Traffic and Safety. In addition, faculty and staff at the Iowa State University Center for Transportation Research and Education were consulted about performance measurement and data within their areas of expertise.

Development of the Des Moines Access Management Plan, 2004

According to Iowa crash records, almost 10% of all crashes in Iowa occur at commercial driveways. Most of these crashes occur on arterials within municipalities. In recent years, nearly a quarter of these crashes have occurred in the Des Moines metropolitan area. This makes the Des Moines metropolitan area a prime candidate for improved access management. Case study research in Iowa has shown that access management is an extremely effective highway safety tool—well-managed routes are, on average, 40% safer than poorly managed routes. The Des Moines metropolitan area has many miles of four-lane, undivided arterials constructed when less was known about the importance of managing access to adjacent land development. This project involved a cooperative effort of the Des Moines Area Metropolitan Planning Organization (Des Moines Area MPO) and the Center for Transportation Research and Education (CTRE) at Iowa State University to develop a comprehensive access management study and program for the Des Moines metropolitan area. The goal of the study is to use the knowledge developed to make improvements that will reduce access-related crashes. It is also anticipated that this project will help local officials make better decisions about access management so that future safety and operational problems can be avoided.

In-Street Yield to Pedestrian Sign Application in Cedar Rapids, Iowa, 2003

Vehicle-pedestrian crashes are a major concern for highway safety analysts. Research reported by Hunter in 1996 indicated that one-third of the 5,000 vehicle-pedestrian crashes investigated occurred at intersections, and 40 percent of those were at non-controlled intersections (Hunter et al. 1996). Numerous strategies have been implemented in an effort to reduce these accidents, including overhead signs, flashing warning beacons, wider and brighter markings on the street, and advanced crossing signs. More recently, pedestrian-activated, in-street flashing lights at the crosswalk and pedestrian crossing signs in the traffic lane have been investigated. Not all of these strategies are recognized as accepted practices and included in the Manual on Uniform Traffic Control Devices (MUTCD), but the Federal Highway Administration (FHWA) is supportive of experimental applications that may lead to effective technology that helps reduce crashes.