Decision making in many agencies responsible for development and management of road networks has come over time to rely substantially on well-defined standards for roadway geometrics and other design details. These standards may be established by the agency itself, by other agencies (concerned, for example, with roadway safety or interstate commerce), or by professional and trade and groups (seeking, for example, to enhance system performance). Such standards are typically intended to provide guidance to design professionals but may over time assume the role of inviolable rules that constrain design decisions.
Recognizing that such constraints may increase project costs, restrict opportunities to address unique characteristics of a site and the surrounding community, and have other deleterious effects, some state transportation agencies have adopted design review processes intended explicitly to identify how project objectives might be better achieved, and possibly with faster construction and lower overall costs, through more tailored accommodation to local conditions and other particular characteristics of the project. Agencies have given these processes such labels as Practical Design, Practical Solutions, or Practical Improvements. NCHRP Synthesis 443: Practical Highway Design Solutions (published in 2013 and available at http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_443.pdf) reviewed a number of these processes.
The processes referred to generally here as Practical Design focus primarily on encouraging project decisions that more precisely address the project’s needs and constraints and avoiding unnecessary costs. Proponents claim that Practical Design encourages flexibility, innovation, and multimodal solutions by maintaining the focus on project need throughout all phases of project development and operation. Practical Design principles encourage evaluation of all components throughout project development to decrease the project cost without sacrificing safety, performance, operations, community livability, economic development, or environmental stewardship. Practical Design is then similar to "flexible design," "context-sensitive solutions," and other design processes that seek to favor sensitivity to a project's particular characteristics over strict reliance on standards.
While current practices at many state transportation agencies are consistent with the concepts of Practical Design, effective implementation of Practical Design approach can be discouraged or prohibited by strict adherence to standards of practice contained in such documents as the Roadside Design Guide, the Policy on the Geometric Design of Highways and Streets (the “Green Book”), Highway Capacity Manual, or state design manuals. Substantial differences in terminology and procedures among guidance documents and agencies practices hinder consideration of the potential consequences of relaxing these standards in particular instances. Newer analysis tools such as those contained in the Highway Safety Manual entail methodology for analyzing design elements in the context of an individual project and can result in substantively safer designs.
The objectives of this research were to engage senior state transportation agency leaders in defining a program to (a) advance a common vocabulary and understanding of Practical Design principles and practices, and (b) identify areas in existing practice manuals and guidelines that may require review by AASHTO’s standing committees for possible modification to enable state transportation agencies to take full advantage of Practical Design principles and practices. The research results are intended to inform discussion within AASHTO’s standing committees and may become a basis for additional research to modify design guides or other practice manuals.
The research engaged DOT senior staff in defining concepts, definitions, and principles, common vocabulary, and other clarification factors describing practical design (PD). A review of current guidelines, regulations, constraints, legal issues was made to identify areas in which action by AASHTO, FHWA, or others may be appropriate to remove impediments to PD implementation and a program of action that AASHTO technical committees may take to facilitate DOT implementation of PD. The research team's report is available for download by clicking here