Integrated Ramp and Ramp Terminal Design
III. RESEARCH PROBLEM STATEMENT
As we move forward with a more sustainable and built environment, it is important to provide an integrated ramp and ramp terminal design that will provide for safe and efficient transportation of the current and future road users. The American Association of State Highway and Transportation Officials’ (AASHTO) A Policy on Geometric Design of Highways and Streets contains general guidelines for the relationship of ramp design speed to the mainline highway design speed, as well as general guidelines for the design speed of ramp terminals, which includes freeway entrance and exit terminals and highway intersections. However, the design of ramps has not traditionally been viewed as an integrated system consisting of the three integral parts which form the ramp: the ramp proper and the appropriate terminals, whether freeway or highway, and on each side of the ramp proper.
A large number of accidents occur on freeway ramps annually. Although ramp design has a major effect on the ability of a freeway and the interchanging roadway to carry traffic safely and efficiently, little research or literature has been published on the concept of the integrated ramp system. Typically, ramp terminals and the ramp proper are designed independent of each other and simply put together in designing a ramp. Ramp design practices should consider driver expectations and behaviors over a full range of geometric and traffic conditions which would include the interchange form, ramp type, the area environment (rural vs. urban) and the functional classification of the two interchanging roadways. The issue of an integrated ramp and ramp terminal design is a complex issue in need of basic research.
The American Association of State Highway and Transportation Officials’ Strategic Highway Safety Plan has identified a need for improved interchange ramp design to reduce the frequency of truck-related fatalities. These crashes typically occur on horizontal curves on the ramp proper, or on deceleration lanes on downgrades. Crashes on interchange ramps have a secondary effect of decreasing mobility not only on the ramp, but on the freeway and intersecting roadway, as a result of an incident.
IV. LITERATURE SEARCH SUMMARY
As noted above, there is limited research on the subject of ramp design as an integrated system. Most of the existing research on ramp design addresses singular issues related to one of the three integral parts of the ramp (freeway-ramp relationships or ramp terminal design). Much of the recent limited literature on ramp design is summarized in NCHRP Synthesis 299. NCHRP 15-31, Design Guidelines for Freeway Mainline Ramp Terminals, begun in 2005, and continued as NCHRP 15-31A may yield some pertinent data relevant to this research. Another project in progress is NCHRP 03-88, Ramp and Interchange Spacing which may yield some useful results or data for this project. The FHWA has also been developing the Intersection/Interchange Safety Analysis Tool (ISAT) which may include some useful safety performance considerations for interchanges and ramps. The Freeway and Interchange Geometric Design Handbook published by ITE in 2006 includes design information and additional resources for ramp design. The Federal SHRP2 program may include data and research related to ramps. A review of completed and ongoing SHRP2 projects would be beneficial. We find that no specific research has examined the important relationship of an integrated ramp terminal and ramp proper design.
V. RESEARCH OBJECTIVE
The objective of this research is to develop integrated ramp design criteria based on quantitative information from actual field observations, theoretical considerations, simulations, or a combination of the three approaches. Research should highlight the safety and operational aspects of integrated ramp design for the full range of interchange forms, ramp types, system vs. service interchange ramps, and area environments (rural vs. urban). The final report should include proposed changes to AASHTO policy, if results support a change.
VI. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD
VII. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION
AASHTO, TRB, and the FHWA continue to support this research. This research need has been updated since its original selection in 2004 by the AASHTO Technical Committee on Geometric Design, the TRB Committee on Geometric Design, and the TRB Committee on Operational Effects of Geometrics at their June 2004 combined meeting. It was identified as one of the ten highest priorities for research. At TRB’s Geometric Design Committee Meeting and Operational Effects combined 2009 summer meeting, the committees once again identified this to be one of the top research needs in geometric design. The research is needed to fill basic performance gaps in current ramp design practices. It will be used nationally in the design of new and reconstructed interchanges that will be in place for many years. If the research identifies recommendation for ramp design changes, this may be incorporated in the AASHTO A Policy on the Geometric Deign of Highways and Streets, state agencies’ design manuals and resources, and local agency design manuals and resources.