BACKGROUND

Turn lanes typically are installed on highways and arterial roads at intersections to improve motor vehicle traffic operations and safety performance. Motor vehicle safety is a primary motivation in determining where and when installation of turn lanes may be appropriate, but experience has shown that crashes at some intersections may increase following the installation, for example, vehicles queued in the turn lane may obstruct the drivers’ view from vehicles crossing on the minor road. In addition, bicycle and pedestrian traffic face increased conflict and crash potential when turns are introduced.

Currently available guidance documents—for example the American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM), the Manual on Uniform Traffic Control Devices (MUTCD), state and local highway design guides, and the AASHTO Policy on Geometric Design for Highways and Streets—offer little assistance to designers and traffic operations professionals for dealing with safety for turn lanes, and there are no generally accepted models for assessing multimodal crash risks at intersections with turn lanes. Ongoing and recently completed NCHRP research is expanding the range of intersection types addressed by crash prediction methods presented in the HSM (in Chapters 10, 11, and 12), and developing safety performance functions (SPFs) and crash modification factors (CMFs) for addressing pedestrian and bicycle safety at intersections (e.g., NCHRP Projects 17-68 and 17-84). However, further work is needed to provide tools for assessing comprehensively multimodal design considerations and safety performance at intersections with turn lanes. Building directly on preceding research, particularly utilizing previously collected data and applying analysis methods from this preceding research, will be cost-effective and very advantageous to state departments of transportation (DOTs).

OBJECTIVE

The objective of this research is to develop (1) SPFs and CMFs to support safety assessment and design decision-making for installation and management of turn lanes at intersections, (2) documentation of this information in forms usable by safety and design practitioners, and (3) guidelines for using the information to perform intersection safety assessments. The research will necessarily entail development of a typology of intersections and turn-lane configurations and application of models for assessing multimodal crash risk as a function of geometric and operational parameters at an intersection. The research results should be useful to responsible state- and local-level practitioners and suitable for inclusion within currently used guidance materials such as the HSM and design guides.

RESEARCH PLAN

The research should include at least the following deliverable products and milestones.

• Interim Report 1 (IR1) presenting (a) a critical review of documented safety performance of a representative selection of turn lane configurations at intersections on urban and suburban roads, with particular emphasis on stop-controlled intersections; (b) a proposed typology of intersection turn lane configurations that will become the basis of subsequent work in the project; and (c) the methodologies to be used for developing SPFs and CMFs to support safety assessment and design decision-making for intersections of the types included in the typology.

• Interim Report 2 (IR2) presenting guidelines and recommendations for the conduct of multimodal safety analyses for design and management of intersections with turn lanes to improve safety performance for all road users.

The final deliverables will include:

• A contractor’s final report with the following:
  • Documentation of the research activities and key findings;
  • SPFs and CMFs to support safety assessment and design decision-making for installation and management of turn lanes at intersections;
  • Documentation of this information in forms usable by safety and design practitioners;
  • Guidelines for using the information to perform intersection safety assessments;
  • Prioritized recommendations for future research; and
  • Other topics identified during the project.
    
    
• A technical memorandum that identifies implementation pathways.

STATUS: Research in progress.