Introduction to the UIIG
The convergence of two or more roads can take the form of an at-grade intersection or a grade-separated interchange. Because an intersection is the point at which multiple pathways directly cross one another, it inherently presents increased opportunities for conflicts between those who traverse it. Intersection collisions are not at all uncommon and often result in severe injuries and fatalities. As depicted below, crashes at or related to intersections have accounted for more than one of every four fatal crashes in the U.S. in recent years.
Total & Intersection-related Fatal Crashes in U.S.
(based on query of NHTSA FARS database).
Intersections can be under various forms of control with respect to assigning the right-of-way for the different users—motorists, bicyclists, and pedestrians. At the highest level, the types of control at intersections can be categorized as those controlled by a traffic signal and those that are not, with the latter group being identified in the Unsignalized Intersection Improvement Guide (UIIG) as unsignalized intersections. The control at unsignalized intersections can be further classified as the following:
- Uncontrolled, for which there are no traffic control devices assigning the right-of-way;
- YIELD sign controlled; and
- STOP sign controlled.
From 2010 to 2012, more than 70 percent of all intersection-related fatal crashes nationwide involved unsignalized intersections. These accounted for approximately one of every six fatal crashes on U.S. roadways.1 As such, and because the vast majority of intersections in the U.S. are unsignalized, it is vital that state and local transportation agencies consider how their design and management practices can better address safety performance, operations, and access for all users at these types of intersections.
The majority of unsignalized intersections are owned and operated by local agencies. Many smaller jurisdictions do not have professional traffic engineers on staff but must frequently make decisions on safety treatments and enhancements at unsignalized intersections. These agencies need practical guidance to assist them in arriving at and justifying these decisions to policymakers and the public.
The UIIG has been developed to address this need. It is prepared to primarily aid local agency practitioners in selecting design, operational, maintenance, enforcement, and other types of treatments to improve the safety, mobility, and accessibility of all users at unsignalized intersections. It is designed under the assumption that an unsignalized intersection (or group of unsignalized intersections) has been identified as having a problem related to traffic safety, operations, or access. The UIIG assists the user in confirming there is indeed a problem and identifying the type and potential cause of the problem, and then offers possible treatments—also identified as countermeasures or strategies—that address the problem. The selection of the desirable treatment for implementation is to be determined by the agency with input from and review by the affected stakeholders within the community.
The UIIG’s primary audience is the agency (or individual) responsible for the roads within a local government jurisdiction, especially those agencies lacking staff with a formal education in highway and traffic engineering principles. However, even trained staff from state and local highway agencies may find this Guide helpful as they address various problems at their unsignalized intersections.
The UIIG is hosted by the Institute of Transportation Engineers (ITE) under the sponsorship of the Federal Highway Administration (FHWA), with full access by all interested parties at no cost. It has been prepared as a web-based resource with the intent that it will be used online and that it can be modified as necessary to incorporate new information. By using the UIIG online, users will have access to the latest information on the various treatments that can be used to improve safety, mobility, and access at unsignalized intersections.
FEEDBACK/QUESTIONS Regarding the UIIG
The UIIG contents are based on information obtained from national guides and manuals, most notably the following:
- Manual on Uniform Traffic Control Devices (MUTCD);
- Various design publications of the American Association of State Highway and Transportation Officials (AASHTO);
- Publications from the National Cooperative Highway Research Program (NCHRP), FHWA, ITE, universities, and others; and
- Best practices observed across the U.S.
Every attempt will be made to keep the information current, including links to yet-to-be published new resources.
ITE and FHWA welcome and encourage feedback with regard to issues encountered in using the UIIG, questions on its contents, and, most importantly, examples of how treatments have been implemented to address intersection problems. Questions and comments may be submitted by clicking on the feedback link at the bottom of the page. It is envisioned that the UIIG will be updated annually, and all user feedback will be considered during each update.