Jerry G. Pigman

EVALUATION OF SPEED LIMITS IN KENTUCKY

The objectives were to examine current criteria and procedures used for setting speed limits and to determine appropriate speed limits for various types of roads. The study involved a review of literature, collection and analysis of speed data, and collection and analysis of accident data. The speed data included moving speed data on various highway types and a comparison of speed data before and after speed limit changes. Accident data were collected at locations where speed limits were changed and also on sections of adjacent Interstates with different speed limits. The speed data indicate that a large percentage of vehicle speeds exceed posted speed limits, with the highest percentage being on urban Interstates and two-lane parkways. The speeds for trucks were slightly lower than for cars. A comparison of speed data at locations where speed limits were changed showed only slight differences. A comparison of accident rates at adjacent sections of Interstate where the speed limit was 88.6 km/hr (55 mph) and 104.7 km/hr (65 mph) did not find a substantial difference in the total, injury, or fatal accident rates. Except where legislatively mandated speed limits apply, the 85th-percentile speed should be used to establish speed limits. Maximum limits are given for various types of roadways. Different speed limits for cars and trucks are recommended for some roadways. An engineering study must be conducted before the speed limit should be changed for any specific section of roadway.

Impact of Shoulder Width and Median Width on Safety

This report contains the findings of research performed to quantify the safety and operational impacts of design element trade-offs and their associated risks. The report details the research performed and includes specific recommended crash prediction models and Accident Modification Factors (AMFs) for shoulder width and median width on rural four-lane roads. Thus, the report will be of immediate interest to engineers in state highway agencies responsible for geometric design and traffic operations and safety.

IMPACT OF PARTIAL GRADUATED DRIVER'S LICENSE PROGRAM ON TEEN MOTOR VEHICLE CRASHES IN KENTUCKY

Teen-driver motor vehicle crashes (MVCs), MVC-related injuries, and MVC-related costs before (1993-1995) and after (1997-1999) the implementation of the teen driver licensing (TDL) program in Kentucky are evaluated. Data collected as part of the study are used to recommend actions to enhance the effectiveness of Kentucky’s TDL program. The study involved the analysis of teen crash data pre-TDL and post-TDL by using data from the Kentucky Accident Reporting System database and the Kentucky Transportation Cabinet driver license file. The study also involved analysis of crash data in relation to crash costs by using the CrashCost software program. Findings indicate that implementation of the TDL program in Kentucky resulted in a substantial (32 percent) reduction in MVC rates for 16-year-old drivers from before the TDL program and a similar reduction in crashes after midnight, fatal crashes, and injury crashes for the 16-year-old age group. Cost analysis indicates an estimated annual reduction of

Evaluation of automated bridge deck anti-icing system

34.2 million in 16-year-old teen-driver MVC-related expenses. However, after a dramatic reduction in the number of crashes for ages 16 to 16.5 (learner permit stage), the number of crashes rose sharply for ages 16.5 to 17, when drivers may have progressed to independent driving. There were no decreases in crash rates for 17- and 18-year-old drivers under the TDL program. Results from this study indicate a need for more effective measures to decrease MVCs for ages 16.5 to 18, such as upgrading to a full graduated driver licensing program.

EVALUATION OF I-75 LANE CLOSURES

Driving in snow and ice can be dangerous. This is especially true on bridges. Under certain cold weather conditions, moisture on bridge decks freezes because of the open air flow under them while the adjacent roadway is unaffected. This creates potentially hazardous driving situations for motorists who may not be expecting a change of condition from the road to the bridge surface. To combat this problem, a bridge deck anti-icing system was installed on a bridge on southbound Interstate 75 at the north interchange to Corbin, Kentucky in October 1997. This system can be actuated early before ice and snow form on the bridge to create hazardous driving conditions. The eleven parapet-mounted/bridge rail-mounted spray nozzles per side treat the two travel lanes and the approach plate with an anti-icing agent. The system uses calcium chloride as the anti-icing agent and sprays eight gallons during each application for the entire bridge. This early chemical application prevents the formation of icy conditions on the bridge deck. After four winter seasons, the anti-icing system located in Corbin, Kentucky had minimal problems associated with it. The system worked efficiently and as expected. However, because of the location on an interstate which is one of the first areas treated during snow maintenance operations and because the bridge is located in a part of the state that does not receive an abundant amount of precipitation, the system was not as effective as first anticipated. It is recommended that this system be used in the following areas and/or conditions: (1) crash prone areas, (2) isolated structures that require the deicing truck to travel an unreasonable distance to treat, (3) remote areas that are difficult to reach in bad weather, or (4) bridges over water which may be more susceptible to freezing moisture.

Development of Procedures for Identifying High-Crash Locations and Prioritizing Safety Improvements

A spot pavement replacement and joint sealing project on I-75 in southern Kentucky during the 1986 construction season involved numerous lane closures. Traffic congestion caused by heavy volumes and late merges resulted in the use of the following traffic control devices to supplement standard lane closure devices: variable message signs, supplemental lane closure warning signs, and rumble strips placed in the lane to be closed in advance of the taper. Because the devices were not typical applications for work zones and because of the potential for applications at other sites, an evaluation study was conducted. Results showed a decrease in the percentage of traffic in the lane to be closed with each successive traffic control device in addition to the standard lane closure devices. There was a general decrease in speeds as traffic approached the taper. The percentage of trucks in the lane to be closed was lower than the percentage in the open lane when the closure was a left lane. Hourly traffic volumes observed in this study (800 to 1,300 vph) did not appear to influence the percentage of traffic in the lane to be closed. The percentage of trucks in both lanes (8.5 to 14.7 percent) did not influence the percentage of traffic in the lane to be closed either. Recommendations from the study included the following: (a) supplemental signs for all long-term closures on high-volume, high-speed four-lane roadways, (b) variable message signs when one-way hourly volumes exceed 1,000 (ADT exceeds 20,000), and (c) application of rumble strips if other devices do not reduce late merges and there is excessive congestion.

Accidents involving vehicles parked on shoulders of limited access highways

The objectives of this study were to review and analyze the current procedures for identifying high-crash locations and evaluating and prioritizing roadway safety improvements at high-crash locations, and to recommend improved methods. Several tasks were undertaken to accomplish these objectives, including the following: review of program guidelines and procedures used by other states to prioritize improvements at high-crash locations; review and documentation of Kentuckys current procedure; update of Kentuckys Crash Buildup Program software to be compatible with the 2000 crash report form; development of new software to assist in estimating the benefits and costs of potential projects for inclusion in the Hazard Elimination Program; and conversion of the dynamic programming software from mainframe to PC. Results from the study include improved methods for identifying high-frequency crash locations and prioritizing those locations after preliminary analyses indicated a need to consider improvements at a crash site. Software was developed to assist in producing a generalized estimate of the benefits of potential projects for inclusion in the Hazard Elimination Program. To use the software, the user must input the improvements to be made, the current level of crashes for the highway segment, and estimated project costs. Adjustments can also be made for key factors such as discount rate and projected traffic growth. Features include a menu of types of improvement projects and related reduction factors, and benefit-cost comparisons for each project. Revisions were recommended for updating and enhancing the Crash Buildup Program to achieve compatibility with the current crash data report form and for translating the dynamic programming module from a mainframe operation to a PC-based system. It appears that an increased level of functionality has been achieved as a result of the series of modifications and improvements.

Investigation of The Impact of Large Trucks on Interstate Highway Safety

This study was conducted to quantify the extent of the problem of accidents involving vehicles on shoulders of limited access highways. Accident data for a three-year period (1985-1987) were collected along with a survey of vehicles stopped on the shoulder on interstates and parkways. While the percentage of all accidents on interstates and parkways involving a vehicle on the shoulder is small (1.8%), the percentage of fatal accidents involving a vehicle on the shoulder is significant (11.1%). The accident data revealed that the majority of shoulder vehicles had stopped for an emergency stop as opposed to a leisure stop with a large number involving an abandoned vehicle. The most common reason for stopping was a mechanical failure. Tractor-trailers were overrepresented in shoulder accidents. An unusually high percentage occurred in the time period of midnight to 6 a.m. The major contributing factors were alcohol involvement and the driver on the mainline falling asleep. Two types of observational surveys were taken. One survey represented what a driver would observe while driving from one point to another on an interstate or parkway. It indicated that a driver would pass (in his direction of travel) an average of about one vehicle on the shoulder every eight miles on an interstate and every 17 miles on a parkway. The second survey was conducted in a circular route such that almost all stops would be observed. The highest percentage of stops were over one hour in length.

EVALUATION OF CHANGE INTERVAL TREATMENTS FOR TRAFFIC SIGNALS AT HIGH-SPEED INTERSECTIONS

This study concentrated on the impact of large trucks on interstate highway safety. The objectives of this study were to investigate the impact of trucks on interstate travel and offer recommendations for improving safety. The procedure involved reviewing the literature, analyzing crash data, discussing the existing situation with the trucking industry, and using the information to develop a list of countermeasures to reduce the number and severity of truck crashes on interstates. The countermeasures were grouped into the general areas of: a) the roadway environment, b) the truck, and c) the driver. The crash data were also analyzed to identify spots and sections on the interstates which had the highest number and rate of truck crashes.

Performance evaluation of breakaway cable terminal end treatments

A large number of traffic accidents at signalized intersections on high-speed roadways occur during or just after the change interval. The green extension system (GES) has been used extensively in Kentucky as a method of alleviating the problem related to the dilemma zone. An alternate method of handling this problem involves warning drivers that the signal indication is about to change from green to red using advance warning flashers (AWF). The objectives of the study were: 1) to evaluate the alternative methods (GES or AWF) which can be used to lessen the problem associated with the dilemma zone which occurs at traffic signals, specifically on high-speed roadways and 2) to determine conditions where use of the AWF may be needed.