Developing a Methodology for Evaluating Design Tradeoffs to Accommodate Multiple Roadway Users
III. Research Problem Statement:
There is increasing recognition that successful roadway geometric design, and in particular successful designs for urban streets, must effectively serve all transportation modes and provide an appropriate balance among those modes. An effective urban street design must often accommodate motor vehicles of many types - passenger vehicles, trucks, buses and sometimes rail transit – while also accommodating non-vehicular modes such as pedestrians and bicyclists. Additionally, space within the right-of-way must typically be provided for roadside hardware, underground and above-ground utilities, and other urban fixtures. Further, the design should be coordinated with the use and “context” of adjacent properties. Any street design that successfully meets all of these objectives is currently often referred to as a “complete street.” The need for more “complete” geometric roadway design in urban areas has been well recognized, and much has been written about the importance of designing for the safe and efficient travel of all user modes along the facility. However, little established practical engineering design guidance exists on how to effectively integrate and balance all transportation modes along the same facility, corridor or intersection. Most available design guidance deals extensively with design for vehicular traffic but does not assess or incorporate the needs (often competing) of other modes to be served. Little information is documented regarding the safety, operational, and usability consequences from the design element tradeoffs of this process.
User needs vary by functional class, presenting a challenge for creating geometric designs that adequately recognize and provide for a mix of transportation modes and the priority that should be given to each. Thus, there is a need to determine the range of users of each highway functional class and assess how best to serve the mix of users found on each class. Another challenge is how to fit a balanced street design into an existing environment with limited right-of-way, congested traffic conditions and other design challenges.
Additionally, pedestrians and cyclists are involved in a disproportionate number of serious collisions at urban intersections because of their vulnerability. Their treatment at high volume signalized intersections is especially critical because the competing demands on the available signal time conflict with heavy turning traffic, long crosswalk exposure distances, etc.
Measures to promote pedestrian and bicycle safety are receiving increased attention because non-motorized users are playing an increasing role in the development of livable and sustainable communities, and livable and sustainable communities are both key policy initiatives for the USDOT. Several pedestrian and bicycle safety treatments have been identified and applied in various locations throughout the US, and there is a need for research to identify the most promising treatments and to promote their nationwide adoption.
IV. Literature Search Summary:
A literature search found extensive work on planning for all travel modes along urban streets, especially on an area-wide basis, but very little work on comprehensive modal design at the level of intersections or individual facilities. Multimodal level of service evaluation, however, was recently investigated and reported in NCHRP Report 616 Multimodal Level of Service Analysis for Urban Streets. A user’s guide for multimodal level of service estimates (autos, buses, bicycles, and pedestrians) is available in NCHRP Web-Only Document 128.
Limited geometric design research is available in this subject area. Several studies have been conducted that dealt with the safety of the various non-vehicle roadway users, but little has been done to correlate the design element tradeoffs that can be implemented to improve the safety and operational level for non-vehicle roadway users.
Documents that should be considered as part of this research include:
· AASHTO, Guide for Planning, Design, and Operation of Pedestrian Facilities (July 2004). This guide is currently being updated and is expected to be published in 2010.
· AASHTO, A Policy on Geometric Design for Highways and Streets. This document is currently being updated and is expected to be published in 2010.
· AASHTO, Guide for Developing Bicycle Facilities. ADA requirements, guidance, and related documents.
· ITE, Designing Walkable Urban Thoroughfares: A Context Sensitive Approach: An ITE Recommended Practice, 2010.
V. Research Objective:
The objectives of the research are to:
· identify the mix of users, including primary and secondary users, that need to be served on various highway functional classes;
· identify the types and designs of facilities needed to serve each of those types of users;
· develop a methodology that can evaluate tradeoffs between designs that focus on accommodating different modes;
· develop examples showing how facilities have been or could be designed effectively as part of the same corridor and intersection; and
· present the results in the form of multimodal design guidelines for specific highway functional classes.
The first objective—identifying mixes of user on specific functional classes—should address the full range of highway functional classes. The latter objectives could also address a range of functional classes or could focus on selected functional classes of interest.
The research should develop examples of projects that have effectively implemented multimodal designs for specific functional classes. It should highlight the features of those designs that allow multiple transportation modes to be served both safely and effectively. The research should also suggest new concepts that could be considered in future projects.
The design guidance developed should be both integrated and multimodal. It should also address the tradeoffs between design elements and safety and operational performance of these facilities. The guidelines should not discuss each transportation mode in separate chapters; an adequate amount of separate material on each mode is available in other sources. Instead, the guidelines should focus on fitting the individual modes together into an integrated facility that meets the needs of each in a balance appropriate for the functional class of the facility. The guidelines should indicate the expected operational and safety performance of alternative approaches to facility design.
The research should include a literature review of previous research and current practice in regard to pedestrian and bicycle facilities design, development of a work plan to achieve the research objectives, collection of applicable field data and other information, evaluation of the safety and operational effects of various combinations of design elements, and preparation of a final report. The final report should include proposed changes to AASHTO documents, if results support a change.
VI. Estimate of Problem Funding and Research Period:
Recommended Funding: $500,000
Research Period: 2 years
VII. Urgency, Payoff Potential, and Implementation:
This research topic was selected 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 combined meeting in June 2009 as a priority issue from among a broader set of problems considered. The research is needed to fill gaps in current roadway design guidance to address and accommodate the needs of all roadway users in the urban setting. The research results should be presented in a stand-alone document that can be used to supplement existing design policies and manuals.
The results of this research could be directly incorporated into standard references, including the AASHTO Green Book (for geometric configurations) and the MUTCD (unique signing, pavement markings, and signalization needs). In addition, the information could be used to update guidebooks such as AASHTO Pedestrian and Bicycle Accommodation guides.
The findings of this project will be directly applicable to the planning, design and operation of urban streets and intersections. They will be of interest to a number of TRB committees and have the potential to provide new material for such authoritative references as the HCM, MUTCD and the AASHTO Green Book, as well as various state standards and guidelines.