Types of Treatments
The purpose of the Unsignalized Intersection Improvements Guide (UIIG) is to assist in determining appropriate treatments that can improve the safety, operations, and accessibility of an unsignalized intersection for all road users.
- Safety is ultimately defined by the absence of crashes and resulting injuries and fatalities. Surrogate measures of safety include minimizing the conflicts between vehicles and between vehicles and other users (i.e., pedestrians and bicyclists).
- Operations typically refers to the flow of traffic and is described in terms of three interrelated measures: delay (for all users), operating speed, and capacity. Efficient operation is achieved when all users can navigate through the intersection without unreasonable delay at an appropriate speed.
- Accessibility, in the context of this guide, relates to providing appropriate accommodations for all non-motorized users, many times with a particular emphasis on pedestrians having mobility or vision disabilities.
Achieving the highest level of safety, operations, or accessibility at a given intersection may come at the detriment of one or both of the other goals. Safety and operations are often correlated—that is, when one improves, the other often benefits, as well. However, this is not always the case. An improvement that increases vehicular speeds may result in higher crash severity or additional crashes. Additionally, modifications to an intersection that improve the safety and operational conditions for vehicular traffic may have the opposite impact on non-motorized users. For example, increasing the corner radius will better accommodate a turning maneuver by a large vehicle but will also result in a longer intersection crossing distance for pedestrians and will allow higher speed turns, thereby increasing their exposure to vehicular traffic. These tradeoffs need to be considered when evaluating improvement alternatives.
Unsignalized intersection improvements can be accomplished by engineering, enforcement, and education-type means—the oft-noted 3 E’s. In general, the UIIG refers to such improvements as treatments, although several other terms (e.g., improvements, measures, and countermeasures) are also used intermittently. Seventy-five (75) treatments are identified and described in the UIIG, with the vast majority classified as engineering treatments. A fact sheet is provided for each to present the following:
- Title—treatment name.
- Description—brief explanation of the treatment to include a photograph when appropriate.
- Problems Addressed—UIIG problem type(s) to which the treatment is applicable.
- Targeted Crash Types—types of crashes (e.g., rear-end, angle, etc.) to which the treatment is applicable.
- Conditions Addressed—intersection characteristics and conditions (e.g., volume levels, road type, crash history, etc.) to which the treatment is applicable.
- Considerations—key points related to treatment selection and implementation.
- Industry Standard—principal section(s) of note within fundamental guidance documents such as the Manual on Uniform Traffic Control Devices (MUTCD) or AASHTO’s A Policy on Geometric Design of Highways and Streets (a.k.a., the Green Book).
- Other Resources—technical publications that provide additional information.
- Select Examples—identification of one or more intersections in the U.S. believed to have the subject treatment, including a hyperlink to internet mapping of the location.
The UIIG treatments are listed by title below, each hyperlinked to its associated UIIG fact sheet. There are no individual fact sheets for the education measures because these are fully described within this section.
Engineering treatments are those that change the physical features or design elements of an unsignalized intersection. For the purpose of this guide, they have been grouped by the following types:
- Traffic Control Device treatments.
- Geometric treatments.
- Shoulder and Roadside treatments.
- Pavement Surface treatments.
- Other Engineering treatments.
Traffic control devices include signs, signals, pavement markings, and other devices used to regulate, warn, or guide traffic. Most of these treatments are significantly less expensive than geometric changes, and some can be installed by maintenance staff or a contractor without the need for extensive engineering design. However, traffic control devices are intended to provide uniform messages and information along all public roads nationwide and, therefore, typically require the approval of the applicable governing body. The proper application of traffic control devices in the U.S. is described in the MUTCD, and a summary of what the MUTCD requires or suggests related to unsignalized intersections can be found in the UIIG’s What Does the MUTCD Say? In addition, several states have adopted their own manual or supplement to the Federal MUTCD that should be reviewed before implementing a traffic control device if a jurisdiction is within that state. Listed below by title are the 37 traffic control device treatments that can address the various problems identified; they are grouped by the type of improvement they provide.
- Install a YIELD Sign
- Install a STOP Sign
- Implement All-Way Stop Control
- Install an Intersection Control Beacon
- Install a Stop Line
- Install a Yield Line
- Install a Stop Beacon
- Install a Traffic Control Signal
- Install Intersection Warning Signs
- Install Advance Traffic Control Warning Signs
- Install an Intersection Conflict Warning System (ICWS)
- Install Post-Mounted Reflective Delineators at the Intersection
Conspicuity Enhancements to Traffic Control Devices
- Increase the Size of a Regulatory or Warning Sign
- Add a Duplicate Regulatory or Warning Sign
- Install a Warning Beacon on a Standard Regulatory or Warning Sign
- Use LED Units within a Regulatory or Warning Sign
- Install Reflective Panels on Sign Posts
- Add Retroreflective Sheeting to the Perimeter of a Warning Sign
- Install Red or Orange Flags to a Regulatory or Warning Sign
- Install Wider Longitudinal Pavement Markings
- Install Center Line Pavement Markings in a Median Crossing
- Install Center Line Pavement Markings on the Minor Road Approach
- Install Dotted Line Pavement Markings
- Install Lane Assignment Pavement Markings or Signing
- Install Pavement Word and/or Symbol Markings
- Install Dotted Turn Path Markings
- Install Raised Pavement Markers
Treatments related to Non-Motorists
- Install or Modify Crosswalk Markings
- Install a Pedestrian Hybrid Beacon (PHB)
- Install a Rectangular Rapid-Flashing Beacon (RRFB)
- Install Bicycle Lane Pavement Markings Across the Intersection
- Install Signs Warning of Pedestrians and Bicyclists
- Add a Beacon to a Standard Speed Limit Sign
- Install Speed Reduction Pavement Markings
- Install a Dynamic Speed Feedback Sign
Geometric treatments involve changes to the physical features of the intersection. In some cases, while geometric changes may be more desirable to address a problem, they are typically more costly, may require the acquisition of right-of-way, and are more likely to require public involvement. As such, geometric treatments may be identified as mid- or long-range improvements and not as a near-term alternative. Listed below are 28 geometric-type treatments:
- Eliminate Turn Movements Using Design Alterations and Channelization
- Replace Left-Turn and Through Movements with a Right-Turn/U-Turn Combination
- Close One or More Legs of the Intersection
- Convert a Four-Legged Intersection to Two T-Intersections
- Convert Two Offset T-Intersections to a Single Four-Legged Intersection
- Close a Median Opening
- Realign the Intersection Approach to Reduce or Eliminate the Skew Angle
- Modify the Horizontal and/or Vertical Alignment of an Intersection Approach
- Reduce an Intersection Curb Radius
- Increase an Intersection Curb Radius
- Install a Raised Intersection
- Reduce the Width of the Travel Lanes on the Major Road Approach
- Install a Splitter Island on the Minor Road Approach
- Install a Left-Turn Lane on the Major Road
- Extend the Left-Turn Lane
- Install a Left-Turn Acceleration Lane
- Provide Offset to Left-Turn Lanes
- Install a Right-Turn Lane along the Major Road
- Extend the Right-Turn Lane
- Install a Right-Turn Acceleration Lane
- Provide Offset to a Right-Turn Lane
- Install a Bypass Lane at a T-Intersection
- Provide a Pedestrian Refuge Island
- Install a Roundabout
- Install a Mini-Roundabout
- Install a Residential Traffic Circle
- Install Curb Extensions at the Crosswalk
- Restrict Driveway Access
Two treatments entail modifications beyond the edge of the travel lane:
Two treatments comprise modifications to the pavement surface on the approach:
- Install Transverse Rumble Strips on the Intersection Approach
- Install a High-Friction Surface Treatment on the Intersection Approach
There are two general engineering-type improvements within the UIIG:
When roads are engineered properly to include traffic control devices that command respect from road users, violations of basic traffic laws should be minimal. However, even with sound engineering, motorists, bicyclists, and pedestrians may violate traffic laws at unsignalized intersections. The following are common violations:
- Failing to yield the right-of-way to other users legally within the intersection.
- Improper turns.
- Failing to come to a full stop when under STOP sign control.
- Speeding (i.e., traveling over the speed limit or too fast for conditions), which usually applies to the major road traffic stream that is not controlled by a STOP or YIELD sign.
- Pedestrian violations, including improper pedestrian crossings and drivers not stopping for pedestrians.
The countermeasures related to violation issues that are within the purview of law enforcement are described below.
To enforce compliance with intersection traffic control, police officers may position themselves such that they can safely view vehicles approaching an intersection. After observing a vehicle proceed into the intersection without yielding the right-of-way as required by the applicable law, the officer would stop the noncompliant vehicle, identify its driver, and issue a citation for the infraction. When repeated at the same location for several days, this type of targeted enforcement is known to increase compliance not only among the individuals receiving citations but also among other drivers who observe the enforcement activities or hear about them from others.
This type of enforcement operation is not as immediately recognizable to drivers passing through the area as compared to other enforcement approaches. Passing drivers can often identify speed enforcement efforts with relative ease, which bears the potential for reinforcement of the speed limit among passing drivers. A marked police vehicle parked near an intersection does not have that same impact. Therefore, agencies may wish to consider (1) placing a portable sign near the police vehicle that reads “Intersection Enforcement” or (2) advertising the enforcement locations on a website or in a radio traffic report. The goal for all traffic enforcement is not to write more citations or to raise funds for the jurisdiction; rather, the goal should be to change driver behavior and improve safety at the intersection.
- Conduct Targeted STOP Sign Enforcement
Failing to come to a full stop when the intersection is controlled by a STOP sign occurs when it is perceived by the motorist that stopping is unnecessary. Enforcement for this violation can be done by traditional targeted police enforcement. Police officers may position their vehicles so they may safely view vehicles as they approach the STOP sign. When repeated at the same location for several days, this type of targeted enforcement is known to increase compliance not only among the individuals receiving citations but also among other drivers who observe the enforcement activities or hear about them from others.
- Conduct Automated STOP Sign Enforcement
Although its use has been limited to date, automated enforcement technology can be applied to target STOP sign violations. With this technology, vehicle movements approaching a STOP sign are tracked. If a vehicle continues past the STOP sign without stopping, an image is captured of the vehicle committing the violation. In some cases, the system is designed to allow a vehicle to pass without capturing a violation image as long as it has slowed below a minimum threshold speed.
Automated enforcement of STOP signs requires the passage of authorizing legislation in most states. Similar to the automated enforcement of red light violations, this countermeasure should be carefully considered after other countermeasures have been explored. There is currently limited guidance published on the implementation of an automated STOP sign violation program.
In 2007, the Mountains Recreation and Conservation Authority (MRCA) in California started the first automated enforcement program for STOP sign violations. These systems were placed in rural park areas. On November 30, 2013, the Washington DC Metropolitan Police Department began to issue citations for STOP sign violations using automated enforcement. The DC program uses a radar-based system to capture images of vehicles not coming to a complete stop at a STOP sign. As shown in the photos, the camera system is placed upstream and uses Doppler radar to determine the speed of each vehicle at the STOP sign. A video clip is saved for each vehicle that does not reduce speed to less than 7 mph at the STOP sign. The video is then reviewed by a police officer to determine if a violation took place.
Automated enforcement operations are planned at 32 stop-controlled intersections in DC. The Metropolitan Police Department is using videos to announce the new automated enforcement initiatives on its website. In light of the program’s recent initiation, there were no evaluation data available at the time this document was published. For further information, contact the Metropolitan Police Department Information Office at (202) 727-8599 or by email at firstname.lastname@example.org.
- Conduct Targeted Speed Enforcement
Traditional speed enforcement activities can be implemented near the intersection where speeding has been identified as a problem. Police officers with handheld radar or laser (light detection and ranging or LIDAR) devices can be positioned to identify the speed of approaching vehicles.
When repeated at the same location for several days, this type of targeted enforcement increases compliance with the individuals receiving citations, as well as with other drivers who see the enforcement taking place or hear about it from others. Additional details may be found in the National Highway Traffic Safety Administration’s Speed Enforcement Program Guidelines.
- Conduct Automated Speed Enforcement
Automated speed enforcement should be viewed as a holistic program and not just as a technology. Successful programs for automated speed enforcement are based on solid problem identification at locations where proper engineering measures are not sufficient to slow speeds to acceptable levels. Automated speed enforcement should never occur where there is an artificially low or unjustified speed limit. Public outreach is essential for the community to develop a keen understanding of the problem and accept automated speed enforcement as a viable countermeasure. Legislation and policies must be established based on the nature of the speeding problem and the community concerns.
Automated enforcement programs may be restricted to specific locations, such as work zones or school zones. Signs are used to encourage drivers to slow down prior to entering the automated enforcement area. This reduces vehicle speeds without resulting in citations being issued for drivers who heed the warning. An enforcement threshold is generally established above the posted speed limit, with thresholds as high as 11 mph above the posted speed limit being common; lower thresholds may be established for work and school zones. Drivers who do not slow down at the warning signs and continue into the enforcement area above the threshold speeds are issued citations. In most cases in the U.S., the owner of the vehicle is issued a citation based on an image of the vehicle registration plate. Some states are required to issue a citation to the driver of the vehicle and must take an image of the driver. If the vehicle owner was not driving at the time of the violation, it is often up to the driver to identify the person who was driving at the time of violation. In all cases, some form of due process is incorporated to allow individuals who receive citations to contest them. Some states or communities have put special restrictions on the use of automated enforcement.
Detailed guidance is available via the U.S. Department of Transportation’s Speed Enforcement Camera System Operational Guidelines.
While pedestrians usually have the right-of-way when crossing at a marked or unmarked crosswalk at an unsignalized intersection, they at times cross improperly, such as darting into the street or between vehicles stopped at an intersection. Drivers have greater difficulty detecting pedestrians in unexpected areas. A pedestrian stepping into traffic from between two cars is at a greater risk of being struck because the cars obstruct the lines of sight between the driver and the pedestrian, thereby reducing the driver’s reaction time.
Signs and physical barriers can be used to direct pedestrians to cross at proper locations. Police officers can be positioned to interdict individual pedestrians whose crossing conduct is contrary to the law or is otherwise unsafe. While officers could issue citations to pedestrians who have violated applicable laws or who are acting carelessly, the issuance of warnings may have a more positive effect and will be better received by the community. Citations may be warranted when the same pedestrian repeatedly violates the law.
Education efforts should be initiated before pedestrian enforcement occurs, even if the enforcement is limited to warnings. Educational efforts are discussed in more detail below.
Regardless of whether their crossing is in accordance with the law, pedestrians are always faced with some level of risk when crossing an intersection. The level of risk increases significantly when the drivers with whom they share the road fail to comply with the law. Pedestrians crossing in a marked or unmarked crosswalk generally have the right-of-way at an unsignalized intersection. Education efforts should be initiated before any pedestrian enforcement is introduced, which will help all road users to better understand the dangers of not yielding properly to a crossing pedestrian. This education effort may include signs at the intersection to stop (or yield) for pedestrians in the crosswalk as appropriate and will help some people to decide on their own to yield the right-of-way for pedestrians. If the enforcement action is to gain community support, the education effort must help people to understand the law and appreciate the risks. If the agency issues press releases on the enforcement actions taken to protect pedestrians, the reach of the education effort is expanded, and with it the likelihood to encourage more people to drive prudently, especially when near pedestrians.
Known as a “decoy” officer, a police officer on foot wearing civilian clothing can be safely positioned to approach the intersection as a pedestrian intending to cross. Drivers who fail to properly yield the right-of-way to the decoy officer may be stopped by another officer in a marked police vehicle waiting nearby and observing the crossing. Cones are typically placed on the curb identifying where the driver should be far back enough to stop for the (decoy) pedestrian and aid in the enforcement effort.
Automated Enforcement for Drivers at Pedestrian Crossings
Automated enforcement may also be used to enforce the laws requiring motorists to stop for pedestrians in marked and unmarked crosswalks. On November 30, 2013, the Washington DC Metropolitan Police Department started to issue citations for drivers who did not stop at crosswalks where pedestrians were actively crossing the street. Using video analytics to determine if pedestrians were in the crosswalk, the radar-based system was designed to capture an image of any vehicle that failed to come to a complete stop before the crosswalk. No evaluation data from this program were available at the time of this publication.
Another critical component of a comprehensive safety program is education, which can manifest itself in several ways:
- Driver licensing and education programs.
- Targeted education programs (focusing on groups such as children, teenagers, and older drivers).
- Public service announcements (PSAs) through various media outlets (e.g., newspapers, television, and the internet).
- Information transmitted to the driving public through roadside signs and other devices.
These activities should be coordinated with the various safety partners among public agencies and safety advocacy groups.
When an agency decides to launch a concerted enforcement effort, it should generally first conduct an education campaign to inform the public of the existing safety problem and the law the safety campaign is meant to support. If the enforcement action is to gain community support, the education effort must help people to understand and recognize the risks of improper conduct at an intersection. This will lead some people to modify their behavior. If the agency issues press releases on any enforcement action taken against drivers, bicyclists, or pedestrians, then the reach of the education component is expanded further.
With regard to unsignalized intersections, education programs and activities should be directed to remind all road users of the following:
- General right-of-way laws at intersections, especially uncontrolled and all-way STOP-controlled intersections, and at pedestrian crossings (with and without crosswalk markings).
- Requirements for stop- and yield-controlled intersections.
- How to safely enter and negotiate an unsignalized intersection.
This is done during driver education programs for new drivers and continued with periodic public service announcements and other education campaigns.
The following specific educational activities should be considered:
- Advising motorists on how a pedestrian hybrid beacon works or how to traverse a roundabout or another nontraditional intersection, particularly if it is the first one in the area. This can be done through websites, PSAs, or press releases to the media to gain their assistance in educating the public. Example guides for educating motorists on the operations and benefits of nontraditional intersections include Washington State DOT’s roundabout guidance and Missouri DOT’s j-turn guidance.
- Advising the public of any targeted enforcement program (e.g., if police plan to target STOP sign violations, adherence to Yield to Pedestrians signs, etc.) at multiple locations.
- Advising motorists of special safety issues of concern at unsignalized intersections:
- Before turning right (or left) at the intersection, deliberately checking for a bicyclist who may be traveling on the vehicle’s right (or left) side.
- Before turning onto a one-way street, checking for pedestrians in both directions (even though vehicular traffic will not be approaching from both directions).
- Properly approaching a stop line and stopping with emphasis on watching for non-motorized users, and safely moving the vehicle forward to a position with adequate sight distance before entering the intersection.
- Considering pedestrians with vision or mobility disabilities.
- Judging safe gaps in oncoming traffic.