The safety of left-turning vehicles at signalized intersections is a concern of the safety community, and guidelines for the installation of left-turn phasing have been developed. The development of guidelines to be considered when determining whether left-turn phasing should be used and the type of phasing that would be appropriate is presented. The guidelines are based on accident data collected for 408 approaches in Kentucky and delay data simulated for a variety of intersection characteristics. The recommendations made take into account many variables, including left-turn volumes, accident rates, product of opposing and left-turn volumes, and left-turn delays. A two-step approach is considered in the decision whether to install left-turn phasing: determine whether protection is needed and then determine the type of protection. The selection of the appropriate left-turn treatment is a process in which trade-offs between safety and delays may be required. Moreover, the use of single rules is usually not adequate to determine the appropriate left-turn treatment; a variety of other factors must be considered.

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.

Periodic renewal of driver licenses is an integral part of the driver licensing procedures for most states. Renewal of driver licenses is usually required every 4 years, and many states conduct vision tests before granting renewal. A few states require additional testing, whereas several states have no vision testing or any other examinations at renewal. Still fewer have additional requirements for older drivers. The increasing percentage of older drivers and the visual changes due to aging or disease are also additional concerns. Thus, it was considered important to systematically review current practices regarding license renewal and retesting and identify potential changes in these procedures. For older drivers, a more frequent renewal period is proposed, accompanied by a vision screening and a medical questionnaire to determine physical and mental status of older drivers.

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 $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.

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