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Objectives and Strategies for Improving Safety at Unsignalized and Signalized Intersections
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This key sheet and the accompanying intersection safety strategy guide sheets are companions to the NCHRP Report 500 series on strategies to reduce crashes at unsignalized (Volume 5) and signalized (Volume 12) intersections.
Objectives and Strategies for Improving Safety at Unsignalized Intersections
| Objectives |
Strategies |
Time |
Cost |
| A Improve management of access near unsignalized
intersections |
A1 Implement driveway closures/relocations (HTML
| PDF) |
Medium |
Moderate |
| A2 Implement driveway turn restrictions (HTML
| PDF) |
Short |
Low |
| B Reduce the frequency and severity of intersection
conflicts through geometric design improvements |
B1 Provide left-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate |
| B2 Provide longer left-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate |
| B3 Provide offset left-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate to High |
| B4 Provide bypass lanes on shoulders at T-intersections (HTML
| PDF) |
Short |
Low |
| B5 Provide left-turn acceleration lanes at divided highway intersections
(HTML
| PDF)
|
Medium |
Moderate |
| B6 Provide right-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate |
| B7 Provide longer right-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate |
| B8 Provide offset right-turn lanes at intersections (HTML
| PDF) |
Medium |
Moderate to High |
| B9 Provide right-turn acceleration lanes at intersections (HTML
| PDF) |
Medium |
Moderate |
| B10 Provide full-width paved shoulders in intersection areas (HTML
| PDF) |
Medium |
Moderate |
| B11 Restrict or eliminate turning maneuvers by signing (HTML
| PDF) |
Short |
Low |
| B12 Restrict or eliminate turning maneuvers by providing channelization
or closing median openings (HTML
| PDF) |
Short |
Low |
| B13 Close or relocate “high-risk” intersections (HTML
| PDF) |
Long |
High |
| B14 Convert four-legged intersections to two T-intersections (HTML
| PDF)
|
Medium |
High |
| B15 Convert offset T-intersections to four-legged intersections (HTML
| PDF) |
Medium |
High |
| B16 Realign intersection approaches to reduce or eliminate intersection
skew (HTML
| PDF) |
Medium |
High |
| B17 Use indirect left-turn treatments to minimize conflicts at divided
highway intersections (HTML
| PDF) |
Medium |
Moderate |
| B18 Improve pedestrian and bicycle facilities to reduce conflicts between
motorists and nonmotorists (HTML
| PDF) |
Medium |
Moderate |
| C Improve sight distance at unsignalized intersections |
C1 Clear sight triangles on stop- or yield-controlled approaches to intersections
(HTML
| PDF)
|
Short |
Low |
| C2 Clear sight triangles in the medians of divided highways near intersections
(HTML
| PDF)
|
Short |
Low |
| C3 Change horizontal and/or vertical alignment of approaches to provide
more sight distance (HTML
| PDF) |
Long |
High |
| C4 Eliminate parking that restricts sight distance (HTML
| PDF) |
Short |
Low |
| D Improve availability of gaps in traffic and
assist drivers in judging gap sizes at unsignalized intersections |
D1 Provide an automated real-time system to inform drivers of the suitability
of available gaps for making turning and crossing maneuvers (HTML
| PDF)
|
Medium |
Moderate |
D2 Provide innovative signs and markings to assist drivers in judging
the suitability of available gaps for making turning and crossing maneuvers
(HTML
| PDF)
|
Medium |
Low |
| D3 Retime adjacent signals to create gaps at stop-controlled intersections
(HTML
| PDF)
|
Short |
Low |
| E Improve driver awareness of intersections as
viewed from the intersection approach |
E1 Improve visibility of intersections by providing enhanced signing and
delineation (HTML
| PDF) |
Short |
Low |
| E2 Improve visibility of the intersection by providing lighting (HTML
| PDF) |
Medium |
Moderate to High |
| E3 Install splitter islands on the minor-road approach to an intersection
(HTML
| PDF)
|
Medium |
Moderate |
| E4 Provide a stop bar (or provide a wider stop bar) on minor-road approaches
(HTML
| PDF)
|
Short |
Low |
| E5 Install larger regulatory and warning signs at intersections (HTML
| PDF) |
Short |
Low |
| E6 Call attention to the intersection by installing rumble strips on intersection
approaches (HTML
| PDF) |
Short |
Low |
| E7 Provide dashed markings (extended left edgelines) for major-road continuity
across the median opening at divided highway intersections (HTML
| PDF) |
Short |
Low |
| E8 Provide supplementary stop signs mounted over the roadway (HTML
| PDF) |
Short |
Low |
| E9 Provide pavement markings with supplementary messages, such as STOP
AHEAD (HTML
| PDF) |
Short |
Low |
| E10 Provide improved maintenance of stop signs (HTML
| PDF) |
Short |
Low |
| E11 Install flashing beacons at stop-controlled intersections (HTML
| PDF) |
Short |
Low |
| F Choose appropriate intersection traffic control
to minimize crash frequency and severity |
F1 Avoid signalizing through roads (HTML
| PDF) |
Long |
High |
| F2 Provide all-way stop-control at appropriate intersections (HTML
| PDF) |
Short |
Low |
| F3 Provide roundabouts at appropriate locations (HTML
| PDF) |
Long |
High |
| G Improve driver compliance with traffic control
devices and traffic laws at intersections |
G1 Provide targeted enforcement to reduce stop sign violations (HTML
| PDF) |
Short |
Moderate |
| G2 Provide targeted public information and education on safety problems
at specific intersections (HTML
| PDF) |
Short |
Low |
| H Reduce operating speeds on specific intersection
approaches |
H1 Provide targeted speed enforcement (HTML
| PDF) |
Short |
Moderate |
| H2 Provide traffic calming on intersection approaches through a combination
of geometrics and traffic control devices (HTML
| PDF) |
Medium |
Moderate |
| H3 Post appropriate speed limit on intersection approaches (HTML
| PDF) |
Short |
Low |
| I Guide motorists more effectively through complex
intersections |
I1 Provide turn path markings (HTML
| PDF) |
Short |
Low |
| I2 Provide a double yellow centerline on the median opening of a divided
highway at intersections (HTML
| PDF) |
Short |
Low |
| I3 Provide lane assignment signing or marking at complex intersections
(HTML
| PDF) |
Short |
Low |
Objectives and Strategies for Improving Safety at Signalized Intersections
| Objectives |
Strategies |
Time |
Cost |
| A Reduce frequency and severity of intersection
conflicts through traffic control and operational improvements |
A1 Employ multiphase signal operation (HTML
| PDF) |
Short |
Low |
| A2 Optimize clearance intervals (HTML
| PDF) |
Short |
Low |
| A3 Restrict or eliminate turning maneuvers (including right turns on red)
(HTML
| PDF)
|
Short |
Low |
| A4 Employ signal coordination (HTML
| PDF) |
Medium |
Moderate |
| A5 Employ emergency vehicle preemption (HTML
| PDF) |
Medium |
Moderate |
| A6 Improve operation of pedestrian and bicycle facilities at signalized
intersections (HTML
| PDF) |
Short |
Low |
| A7 Remove unwarranted signal (HTML
| PDF) |
Short |
Low |
| B Reduce frequency and severity of intersection
conflicts through geometric improvements |
B1 Provide/improve left-turn channelization (HTML
| PDF) |
Medium |
Moderate |
| B2 Provide/improve right-turn channelization (HTML
| PDF) |
Medium |
Moderate |
| B3 Improve geometry of pedestrian and bicycle facilities (HTML
| PDF) |
Short |
Low |
| B4 Revise geometry of complex intersections (HTML
| PDF) |
Long |
High |
| B5 Construct special solutions (HTML
| PDF) |
Long |
High |
| C Improve sight distance at signalized intersections |
C1 Clear sight triangles (HTML
| PDF) |
Short |
Low |
| C2 Redesign intersection approaches (HTML
| PDF) |
Long |
High |
| D Improve driver awareness of intersections and
signal control |
D1 Improve visibility of intersections on approach(es) (HTML
| PDF) |
Short |
Low |
| D2 Improve visibility of signals and signs at intersections (HTML
| PDF) |
Short |
Low |
| E Improve driver compliance with traffic control
devices |
E1 Provide public information and education (HTML
| PDF) |
Short |
Low |
| E2 Provide targeted conventional enforcement of traffic laws (HTML
| PDF) |
Short |
Moderate |
| E3 Implement automated enforcement of red-light running (cameras) (HTML
| PDF) |
Medium |
Moderate |
| E4 Implement automated enforcement of approach speeds (cameras) (HTML
| PDF) |
Medium |
Moderate |
| E5 Control speed on approaches (HTML
| PDF) |
Medium |
Moderate |
| F Improve access management near signalized intersections |
F1 Restrict access to properties using driveway closures or turn restrictions
(HTML
| PDF) |
Short |
Low |
| F2 Restrict cross-median access near intersections (HTML
| PDF) |
Short |
Low |
| G Improve safety through other infrastructure
treatments. |
G1 Improve drainage in intersection and on approaches (HTML
| PDF) |
Medium |
Moderate |
| G2 Provide skid resistance in intersection and on approaches (HTML
| PDF) |
Medium |
Moderate |
| G3 Coordinate closely spaced signals near at-grade railroad crossings
(HTML
| PDF)
|
Medium |
Moderate |
| G4 Relocate signal hardware out of clear zone (HTML
| PDF) |
Short |
Moderate |
| G5 Restrict or eliminate parking on intersection approaches (HTML
| PDF) |
Short |
Low |
Key to the Guide Sheets
Strategy:
Strategy Name
Where to Use:
This contains a brief description of where you might use this particular strategy and under what circumstances.
Details:
This section contains a brief description of the strategy and how it may be applied to address the safety concern.
Key to Success:
This section will discuss some critical things to consider when implementing this particular strategy in order to be successful.
Issues:
This section will discuss various issues that need to be addressed during the implementation process.
Time frame:
Time frames will naturally vary based on numerous factors (agency procedures, number of stakeholders, need for additional right-of-way). The scale is meant as a general guide. One circle indicates a short time frame for implementation perhaps in as little as a few months or up to 1 year. Example short term strategies include signage improvements, signal timing changes, and sight distance improvements. Two circles indicates a medium time frame of 1-2 years. Example medium term strategies include channelization improvements, system-wide signal improvements, and minor geometric improvements. Three circles indicates a longer time frame of over 2 years. These strategies will typically require major construction or right-of-way acquisition.
Costs:
Costs will also vary considerably and are affected by local conditions. Costs are ranked as: low, moderate, moderate to high, and high. The scale is meant to reflect costs relative to the other strategies described in the category (signalized or unsignalized).
Effectiveness:
This section will discuss any research or evaluations that have been done to ascertain the effectiveness of the particular strategy. Three descriptors are used to identify to what degree the strategy has been evaluated:
Proven: Those strategies that have been used in one or more locations and for which properly designed evaluations have been conducted that show it to be effective. These strategies may be employed with a good degree of confidence, but with the understanding that any application can lead to results that vary significantly from those found in previous evaluations. Crash reduction factors reported are typically based on valid research methods.
Tried: Those strategies that have been implemented in a number of locations and may even be accepted as standards or standard approaches, but for which there have not been found valid evaluations. These strategies, while frequently or even generally used, should be applied with caution; users should carefully consider the attributes cited in the guide and relate them to the specific conditions for which they are being considered. There can be some degree of assurance that implementation will not likely have a negative impact on safety and will very likely have a positive one. Crash reduction factors reported are not necessarily based on valid research methods and should be used with caution.
Experimental: Those strategies that have been suggested and that at least one agency has considered sufficiently promising to try on a small scale in at least one location. These strategies should be considered only after the others have been determined to be inappropriate or unfeasible. Even where they are considered, their implementation should initially occur using a very controlled and limited pilot study that includes a properly designed evaluation component.
Compatibility:
This section will make note of any compatibility issues with other strategies.
Supplemental Information:
This section will guide the reader to other information relevant to this strategy such as documents and Web sites.
For more information contact:
FHWA Office of Safety Design
E71, 1200 New Jersey Avenue SE
Washington, D.C. 20590
(202) 366-9064
http://safety.fhwa.dot.gov
FHWA Resource Center – Safety and Design Team
19900 Governors Drive Suite 301
Olympia Fields, IL 60461
(708) 283-3545
http://www.fhwa.dot.gov/resourcecenter
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