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FHWA Home / Safety / Geometric Design / Key Components

Key Components

Access Management

Access Management seeks to improve traffic distribution, reduce vehicle conflicts, and reduce crashes, by providing better control of driveway access points. The result is a roadway that functions safely and efficiently for its useful life, and a more attractive corridor. A good access management practice can offer a great combination among operation, geometric design and safety.

General Benefits of Access Management

"By managing roadway access, government agencies can extend the life of roads and highways, increase public safety, reduce traffic congestion, and improve the appearance and quality of the built environment. Not only does access management preserve the transportation functions of roadways, it also helps preserve long-term property values and the economic viability of abutting development. From an environmental perspective, improved traffic flow translate into greater fuel efficiency and reduced vehicular emissions. Consolidating access roads is also less damaging to rural landscapes or environmentally sensitive areas that numerous individual private drives." ("Access Management Manual" - TRB, 2003)

Interactive Highway Safety Design Model (IHSDM)

IHSDM is a suite of software analysis tools for explicit, quantitative evaluation of safety and operational effects of geometric design decisions during the highway design process. It culminates a multiyear research and development effort conducted by the Federal Highway Administration.

IHSDM is intended for use throughout the highway design process from preliminary planning and engineering through detailed design to final review. It may be used both for projects to improve existing roadways and projects to construct new roadways. Intended users include highway project managers, designers, and traffic and safety reviewers in State and local highway agencies and engineering consulting firms. The 2014 release of IHSDM has six evaluation modules: (1) crash prediction, (2) policy review, (3) design consistency, (4) intersection review, (5) traffic analysis, (6) driver/vehicle. The IHSDM - HSM Predictive Method 2014 Release may be downloaded free-of-charge at http://www.ihsdm.org.


A roundabout is a one-way, circular intersection in which traffic flows around a center island. To reduce crashes and improve intersection safety, FHWA recommends the use of roundabouts, where appropriate. Roundabouts are designed to meet the needs of all road users-drivers, pedestrians, pedestrians with disabilities, and bicyclists. Proper site selection and pedestrian channelization are essential to making roundabouts accessible to all users.

A roundabout eliminates some of the conflicting traffic, such as left turns, which cause crashes at traditional intersections. Because roundabout traffic enters or exits only through right turns, the occurrence of severe crashes is substantially reduced. Small angle collisions that may occur as a result of a right-hand turn are typically less severe than other types of collisions.

Page last modified on October 15, 2014
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