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FHWA Home / Safety / Intersection / Intersection Safety Needs Identification Report

Intersection Safety Needs Identification Report

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Intersection Safety Categories and Associated Strategies
1. Intersection Design Options

1.1 Access Management

Exhibit III – Intersection and Access Fatalities - 1998-2007

not applicable

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Intersection Fatalities (Source: Preliminary 2007 FARS data)

9,240

8,924

8,689

8,922

9,273

9,362

9,176

9,238

8,850

8,657

Access Fatalities (Intersection and Junction Fatalities in the Context of Access Management, Edward R. Stollof, Prepared for:
TRB 8th National Conference on Access Management, July 2008.)

820

932

774

837

874

1,105

1,208

1,263

1,317

1,397

Access fatalities in the vicinity of intersections have increased by more than 41 percent in the last 10 years, from 820 in 1998 to 1,397 in 2007 (Exhibit III).

Access fatalities are those that occur at driveways, alley accesses, entrance or exit ramps, and crossovers.  

Facts (FHWA. Presented at TRB Access Management Conference. Baltimore, MD  2009.)

A number of tools and techniques can be used as part of an access management plan. They include physical design as well as policy-related techniques that address land development and roadway design standards.

Implementing access management tools and techniques can be difficult.  They are not always initially understood or acceptable to residents, road users, and businesses, often due to concerns about impeded mobility, access, or safety.  Governments must do their part to educate and demonstrate to the affected citizenry the potential positive impacts of access management techniques—for both individuals and the collective community.

Recommendations

  1. Continue research on the safety and cost benefits of access management techniques.
  2. Conduct outreach and education on the safety and cost benefits of access management techniques. 
  3. Increase implementation of access management techniques. 

1.2 Roundabouts

Issues.  Roundabouts have been shown to improve safety by slowing traffic and reducing the number and severity of the conflicts between the different movements.  The National Cooperative Highway Research Program found that the installation of roundabouts led to a 35 percent reduction in total crashes and a 76 percent reduction in crashes causing injuries or fatalities.

Exhibit IV – Intersection Conflicts: Roundabout vs. Conventional Intersection

Exhibit 4 - diagram - illustrates the difference in the number of traffic movements in a typical intersection and a roundabout.  A plan view of a typical intersection is shown on the left, showing the number of diverging movements (8) represented by filled circles, merging movements (8) represented by half-filled circles, and crossing movements (16) represented by empty circles that occur in this type of intersection.  On the right, a plan view of a roundabout uses the same symbols to illustrate the fewer diverging movements (4) and merging movements (4) that occur on a roundabout.

Because traffic enters and exits the roundabout using only right turns, the number and types of hazardous traffic conflicts are lessened, as illustrated in Exhibit IV. The exposure for severe angle crashes is substantially reduced or eliminated.  All approaching vehicles are required to yield to vehicles already in the circulatory roadway, so rear-end crashes from vehicles stopping suddenly are much less common.

However, pedestrian crossings are potentially more challenging because entering traffic does not have to stop if there are sufficient gaps.  On the other hand, pedestrians have a lower risk of being involved in a severe crash because of the lower vehicle speeds and having to cross only one roadway at a time.

The use of roundabouts is common in other countries and is gaining momentum in the U.S.  The safety benefits are well-documented.  The reluctance to move toward more widespread construction of roundabouts in this country is based primarily on unfamiliarity and tradition, which is slowly being overcome as more of them are built and the many benefits become obvious. The upcoming Highway Safety Manual has a section on the safety effectiveness of roundabouts.  Increasing the number of roundabout installations would not only improve users' familiarization and expectations, but would also significantly reduce the numbers of serious injuries and fatalities at U.S. intersections. 

Recommendations

  1. Consider roundabouts as viable alternatives for new and redesigned intersections.
  2. Conduct outreach to overcome opposition by state and local officials who are unfamiliar with the safety and operational benefits of roundabouts.
  3. Educate engineers on how to properly plan and design roundabouts, including avoiding past design and construction errors.
  4. Educate and familiarize road users about roundabout usage and benefits.

1.3 Alternative Intersection Designs

Issues.  The most common severe crashes at intersections are angle crashes.  The typical traffic control devices (stop sign or traffic signal) require drivers on one path to yield or stop for those on the conflicting path through the intersection.  Some alternative designs remove these conflicts (angle crossings) replacing them with less-severe conflict types (merge/diverge).  These types of intersections can address the safety problems and still maintain the mobility of the higher-speed, high-volume routes. They can be more cost-effective than grade-separated interchanges, especially for lower-volume routes crossing the major routes.  A few of these alternative intersection designs are shown in Exhibit V  For additional information, see FHWA publication Alternative Intersections/Interchanges: Informational Report.

Exhibit V – Alternative Intersection Designs

Quadrant roadways remove the left-turning traffic from the large intersections, replacing the movement with multiple right turns or a left turn at a T intersection.  This configuration reduces the number of left-turn crossing conflicts from 12 to 4, providing potential for a major reduction in left-turn crashes.

Quadrant roadway - diagram

Median U-turn intersections replace the left turns with right turns and U-turns on the major and minor approaches.  Median crossovers are very common in Michigan.  The collision rate along road sections utilizing the median crossovers was 49 to 52 percent less for signalized corridors having more than one traffic signal per mile.

Median U-turn intersection - diagram

Restricted crossing U-turn intersections are similar to median U-turn crossovers, but allow left turns from the major street only.  This design is appropriate where there are high volumes on the major route and relatively small volumes on the minor route.
Pedestrian safety may be increased because there are medians between the different channelized movements that provide refuge.

Restricted crossing U-turn intersection - diagram

Recommendations

  1. Consider alternative designs at intersections with safety and/or operational problems.
  2. Perform outreach to inform transportation agencies and the public of the benefits of alternative intersection designs.
  3. Provide education on the selection, evaluation and design of alternative intersections.
  4. Continue to evaluate the safety implications of alternative intersection designs.

1.4 Rural Intersection Safety

Issues.  Safety performance of conventional, two-way, stop-controlled intersections on rural highways declined as volumes on these minor roadways increased. Several strategies may be applied at rural areas to improve safety at problematic intersections.

Many fatalities occur at low-volume, stop-controlled intersections, but there are so many of these intersections that it is not practical to reconstruct all of them.  Low-cost treatments that can be done on a widespread basis are needed.

Low-cost treatments that have been applied have included enhanced traffic signs and pavement markings, flashing beacons, turn lanes or bypass lanes, intersection lighting, rumble strips, and increased enforcement.

These treatments are effective in getting the driver’s attention because they are enhancements at intersections that meet minimum requirements of the Manual on Uniform Traffic Control Devices

Enhanced signing, such as larger signs, signs with LED lights, or sign-mounted flashers to get the driver’s attention, help drivers to observe potentially unsafe conditions and react in time to take safe action.

Overhead flashing beacons call attention to the stop-controlled intersection. 

Transverse or longitudinal rumble strips, pavement markings, lane narrowing, and splitter islands can reduce approach speeds and increase awareness of the intersections.  Increased enforcement tends to reduce intentional violations of stop signs. 

Recommendations

  1. Promote programs and action plans that encourage proactive, systematic application of low-cost treatments rather than focusing only on the locations where high numbers of severe crashes have occurred.
  2. Develop a best practice guide for rural low-volume intersection improvements, for use by local county engineers and managers of tribal lands, national parks, and others who implement safety improvements.
  3. Promote the continued funding of high-risk rural roads, including rural intersection treatments, into future reauthorization legislation.
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Page last modified on September 4, 2014.
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