A Guide for AddressingUnsignalized Intersection Collisions

One of a Series of Guides to Help States Improve Highway Safety

Intersection CrashesLarge Part of the ProblemIntersections constitute only a small part of the overallhighway system, yet intersection-related crashesconstitute more than 50 percent of all crashes in urbanareas and more than 30 percent in rural areas. Nearly36 percent of crashes at unsignalized intersectionsinvolve injuries and 9 percent involve fatalities.

Representative Countermeasures

Improve management of access near unsignalizedintersections: Improve driveway closures andrelocations, and implement driveway turn restrictions.

Reduce the frequency and severity of intersectionconflicts through geometric design improvements:Provide left/right-turn lanes or longer or offsetleft/right-turn lanes at intersections; provide by-passlanes on shoulders at T-intersections; provide left-turnacceleration lanes at divided highway intersections;provide full-length paved shoulders in intersectionareas; restrict or eliminate turning maneuvers bysigning, providing channelization, or closing mediaopenings; close or relocate high-risk intersections;convert 4-legged intersections to 2 T-intersections;convert offset T-intersections to 4-legged intersections; realign intersection approaches to reduce or eliminateintersection skew; use indirect left-turn treatments tominimize conflicts at divided highway intersections;

improve pedestrian and bicycle facilities to reduceconflicts between motorists and non-motorists.

Improve sight distance at unsignalizedintersections: Clear sight-triangles on stop- oryield-controlled approaches to intersections, clearsight triangles in the medians of divided highways near intersections, change horizontal and/or verticalalignment of approaches to provide more sightdistance, and eliminate parking that restricts sightdistance.

Improve availability of gaps in traffic and assistdrivers in judging gap sizes at unsignalizedintersections: Provide an automated real-timesystem to inform drivers of the suitability of availablegaps for making turning and crossing maneuvers,provide roadside markers or pavement markings toassist drivers in judging the suitability of gaps formaking turning and crossing maneuvers, and retimeadjacent signals to create gaps at stop-controlledintersections.

Improve driver awareness of intersections asviewed from the intersection approach: Improvevisibility of the intersection by providing enhancedsigning and delineation and lighting; install splitterislands on the minor-road approach to an intersection;

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provide a stop bar or wider stop on minor roadapproaches; install regulatory and warning signs atintersections; call attention to the intersection byinstalling rumble strips on intersection approaches;provide dashed markings for major road continuityacross the median opening at divided highwayintersections; provide supplementary stop signsmounted over the roadway; provide pavementmarkings with supplementary messages, such asSTOP AHEAD; provide improved maintenance of stopsigns; and install flashing beacons on stop-controlledintersections.

Choose appropriate intersection control tominimize crash frequency and severity: Avoidsignalizing through roads, provide all-way stop controlat appropriate intersections, and provide roundaboutsat appropriate intersections.

Improve driver compliance with traffic-controldevices and traffic laws at intersections: Providetargeted enforcement to reduce stop sign violations,and provide targeted public information and educationon safety problems at specific intersections.

Reduce operating speeds on specific intersectionapproaches: Provide targeted speed enforcement,provide traffic calming on intersection approachesthrough a combination of geometrics and traffic control devices, and post appropriate speed limit onintersection approaches.

Guide motorists more effectively through complexintersections: Provide turn path markings, providedouble-yellow centerline on the median opening of adivided highway at intersections, and providelane-assignment signing or marking at complexintersections.

How the Implementation Guide Helps You

The guide lists practical countermeasure strategies,categorized by relative cost to implement. Many of these strategies have been formally evaluated to demonstrateeffectiveness. Other strategies lack formal evaluation, but have been implemented with promising results.

The guide lays out the technical attributes of eachcountermeasure strategy in detail: target audience,expected effectiveness, keys to success, potentialdifficulties, appropriate measures and data, andassociated need for support services.

The guide reveals organizational, institutional, and policyissues; issues affecting implementation time; costsinvolved; training and other personnel needs; andlegislative needs (if any).

Web-Based Support for More Information

Backing up the guide is a series of appendixes andexhibits developed specifically to provide in-depthinformation useful to anyone implementing this part of the Strategic Highway Safety Plan, together with a collectionof general knowledge sharing documents providingbackground, data, and information of significant value tostate and local implementers.

This guide is one in a series developed to assist states in their efforts to improve highway safety. copies of theplan, the guides, along with the Integrated SafetyManagement System, Self-Assessment Tool, relateddocuments, may be obtained on the Internet atsafety.transportation.org.

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Printed copies of the guides can be obtained from:Transportation Research BoardNational Cooperative Highway Research Program500 Fifth St., NWWashington, DC 20001-2721

Telephone: 202-334-3213

Implementing the AASHTO Strategic Highway Safety Plan