Innovative intersections

What is a bowtie?

• An intersection where left-turn movements are completed at an adjacent roundabout.
• There are roundabouts on the side street, before and after the main intersection.
• The roundabouts can have two to four legs.
• Traffic entering the roundabout slows and yields to traffic already inside.
• The roundabouts' diameters vary depending on speed, volume, vehicle size and number of legs.

When should it be considered?

• With moderate to heavy through traffic volumes and low to moderate left-turn traffic volumes.
• With narrow or nonexistent medians and/or limited right of way to expand.

Benefits

• Improved safety: Reduces the number of points where motorists, pedestrians and bicyclists may cross paths. Promotes lower speeds at the roundabouts, giving drivers more time to react.
• Increased efficiency: Since there are no left turns at the main intersection and the adjacent intersections are yield controlled, a bowtie has fewer traffic signal phases, which reduces stops and delay.
• Shorter wait times: Fewer traffic signal phases means less time stopped at the main intersection.
• Cost effective: Can be more cost effective than adding lanes to increase capacity.

How to navigate

Below shows how to navigate a bowtie intersection. View a larger version or watch the video.

What is a CGT?

• Intersection design where one major street direction of travel (the top side of the “T”) can pass through the intersection without stopping, and the opposite major street direction of travel is typically controlled by a traffic signal.
• Left-turn vehicles from the side street use a channelized receiving lane on the major street to merge onto the major street.
• Intersection is typically signalized but can also be designed without a traffic signal.

When should it be considered?

• At intersections:
• With three legs.
• With heavy through traffic volumes on the major street.
• With moderate to low left-turn traffic volumes on the side street.
• Where there are no driveways along the major street opposite the side street.
• With a limited number of pedestrian crossings across the major street or with an alternative pedestrian crossing location nearby.

Benefits

• Improved safety: Channelizing left-turn vehicles from the side street reduces the potential for angle crashes.
• Increased efficiency: One direction of travel on the major street is free-flow, and, as a result, more green time can be provided to the other movements, reducing delay.
• Free-flow in one direction: One direction of travel on the major street never stops, which improves traffic signal synchronization and reduces corridor travel times.

How to navigate

Below shows how to navigate a CGT intersection. View a larger version or watch the video.

What is a DLT?

• Intersection design where left-turn vehicles cross to the other side of the opposing through-traffic in advance of the main intersection.
• Left turns and opposing through movements occur simultaneously at the main intersection.
• Intersection can be designed as a partial DLT, with crossovers for left turns only on the major street, or a full DLT, with crossovers for left turns on both the major and side streets.
• Main intersection and crossovers are signalized and timed to work together to minimize stops.

When should it be considered?

• At intersections:
• With moderate to heavy traffic volumes in all directions.
• Where opposing legs have similar through traffic volumes.
• With heavy left-turn traffic volumes.
• With a limited number of driveways or access points near the intersection.

Benefits

• Improved safety: Reduces and spreads out the number of potential conflict points where vehicles may cross paths.
• Increased efficiency: Simultaneous movement of protected left turns and opposing through-movements allows for only two traffic signal phases rather than the typical four phases, which reduces delay.
• Better synchronization: Elimination of left-turn traffic signal phases and synchronization of the main intersection and crossover traffic signals allows through-traffic to spend less time stopped, which improves corridor travel times.

How to navigate

Below is how to navigate a DLT intersection. View a larger version or watch the video.

What is an echelon?

• A grade-separated intersection where one approach on both roadways is elevated to create a pair of. 
• Both intersections are signalized and operate like conventional one-way street intersections.
• There are no free-flow movements.
• Uses retaining walls to elevate half of the roadway while the other half continues at-grade.
• All pedestrian sidewalks and crosswalks are at grade. However, a staircase or ramp may be required in some locations due to retaining walls or other obstacles.

When should it be considered?

• With heavy traffic where main and side street traffic volumes are similar.
• Where an at-grade conventional intersection is not sufficient for the traffic.
• Where there is limited right of way to expand.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths and decreases the potential for angle crashes.
• Increased efficiency: Each intersection operates with only two traffic signal phases, allowing the intersection to handle more traffic.
• Shorter wait times: Fewer traffic signal phases means less time stopped at the intersection.
• Cost savings: The echelon can have a narrower cross section and may be more cost effective than constructing a traditional diamond interchange.

How to navigate

Below shows how to navigate an echelon intersection. View a larger version or watch the video.

What is a median U-turn (MUT)?

• Intersection design where left-turn vehicles from one or both roads make U-turns at dedicated median openings to complete the desired movement.
• Intersection can be designed with median U-turns on one or both roads.
• Median U-turns can be designed as signalized, stop controlled, or yield controlled.

Where should it be considered?

• On median-divided highways.
• At intersections.
• With moderate to heavy through-traffic volumes and low to moderate left-turn traffic volumes.
• With three or four legs.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths and decreases the potential for right-angle crashes.
• Increased efficiency: Eliminates left-turn movements from the main intersection, allowing for fewer traffic signal phases, which reduces delay and increases capacity.
• Shorter wait times: Fewer traffic signal phases means less time stopped at the main intersection.
• Cost effective: A MUT can be more cost effective than adding lanes to increase capacity.

How to navigate

Below shows how to navigate a MUT intersection. View a larger version or watch the video.

What is a quadrant roadway (QR)?

• Intersection design with one main intersection and two secondary intersections that are linked by a connector road in any quadrant of the intersection.
• Left-turn vehicles from all four legs of the main intersection use the secondary intersections and connector road, instead of the main intersection, to complete left-turn movements.
• Secondary intersections are typically signalized but can also be unsignalized.
• When all three intersections are signalized, traffic signals are timed to operate together.

When should it be considered?

• At locations with an existing roadway that can be used as the connector roadway.
• At intersections:
• With four legs.
• With heavy through and left-turn traffic volumes on the major and side streets.

Benefits

• Improved safety: Reduces and spreads out the number of points where vehicles may cross paths.
• Increased efficiency: Rerouting left turns allows for fewer traffic signal phases at the main intersection, which means less time waiting for through and right-turn vehicles.
• Better synchronization: Synchronization of three signalized intersections improves corridor travel times on both the major and side streets.

How to navigate

Below is how to navigate a QR intersection. View a larger version or watch the video.

What is an RCUT?

• Intersection design where all side street movements begin with a right turn.
• Side street left-turn and through vehicles turn right and make a U-turn at a dedicated downstream median opening to complete the desired movement.
• Main intersection and median U-turns can be designed as signalized, stop controlled or yield controlled.

When should it be considered?

• On median-divided highways.
• At intersections:
• With heavy through and / or left-turn traffic volumes on the major street.
• With low through and left-turn traffic volumes on the side street.
• With three or four legs.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths and eliminates the potential for head-on crashes.
• Increased efficiency: Each direction of the major street can operate independently, creating two one-way streets and increasing the overall intersection capacity.
• Shorter wait times: Fewer traffic signal phases means less stopping for arterial vehicles and allowing only right turns from side street vehicles means less waiting.
• Cost-effective: An RCUT can be more cost effective than adding lanes to improve capacity.

How to navigate

Below is how to navigate an RCUT. View a larger version or watch the video.

What is a roundabout?

• A circular, unsignalized intersection where all traffic moves counterclockwise around a central island
• Traffic entering the roundabout slows down and yields to traffic already inside the roundabout
• Roundabouts can be designed with one or more circulating lanes
• Design options allow for right turns to be channelized to bypass the circulating lanes

When should it be considered?

• At intersections:
• With heavy left-turn traffic or with similar traffic volumes on each leg.
• With crashes involving conflicting through and left-turn vehicles.
• With limited room for storing vehicles.
• Where there are limited nearby driveways.

Benefits

• Improved safety: Reduces the number of points where vehicles can cross paths and eliminates the potential for right-angle and head-on crashes.
• Increased efficiency: Yield-controlled design means fewer stops, fewer delays and shorter queues.
• Safer speeds: Promotes lower vehicle speeds, giving drivers more time to react.
• Long-term cost effectiveness: No traffic signals means lower long-term costs for operations and maintenance.
• Aesthetics: Allows for landscaping and beautification.

How to Navigate

Below shows how to navigate a roundabout intersection. View a larger version or watch the video.

What is a mini roundabout?

• A circular, unsignalized intersection where all traffic moves in a counter-clockwise direction around a central island.
• Traffic entering the mini roundabout slows down and yields to traffic already inside.
• The defining feature is a fully traversable central island and splitter islands that larger vehicles can drive over.
• Flush central islands may be appropriate for those frequently used by buses.
• Uses the same operating principles of modern roundabouts.

When should it be considered?

• With heavy left-turn traffic or with similar traffic volumes on each leg.
• With low truck and bus volumes.
• With crashes involving through and left-turn vehicles.
• With a posted speed of 35 miles per hour or less.
• Where vehicles from adjacent intersections will not queue into the roundabout.

Benefits

• Improved safety: Reduces the number of points where vehicles can cross paths and eliminates the potential for right-angle and head-on crashes.
• Increased efficiency: Yield-controlled design means fewer stops, less delay and shorter queues for overall improved efficiency.
• Safer speeds: Promotes lower vehicle speeds, giving drivers more time to react.
• Long-term, cost-effective savings: No traffic signal equipment means lower long-term costs for operations and maintenance.

How to navigate

Below shows how to navigate a mini roundabout intersection. View a larger version or watch the video.

What is a single loop?

• An intersection where all four left-turn movements and some, or all, right-turn movements are rerouted onto a connector road.
• Major and side streets are grade-separated.
• Single loops are typically signalized, but not necessarily.
• A staircase or ramp may be used to shorten pedestrian paths between the elevated and at-grade roadways.

When should it be considered?

• At intersections with low to medium left-turn traffic volumes.
• To connect a high-speed street with heavy traffic volumes to a slower, less-traveled street.
• To connect existing grade-separated streets.

Benefits

• Improved safety: Reduces and spreads out the number of points where vehicles, pedestrians and bicyclists may cross paths.
• Increased efficiency: Rerouting left turns allows for fewer traffic signal phases, which means less time waiting for through and right-turn vehicles.
• Better synchronization: Synchronization of the two signalized intersections improves corridor travel times on both the major and side streets.

How to navigate

Below shows how to navigate a single loop intersection. View a larger version.

What is a split intersection?

• It divides traffic on a major street into two one-way streets that meet the side street at separate signalized intersections.
• It is similar to a traditional diamond interchange without grade-separated roadways.

When should it be considered?

• At congested suburban intersections with heavy left-turn traffic volumes.
• In urban areas where two-way streets can be converted to one-way streets.
• Where grade-separation may be necessary in the future.

Benefits

• Improved safety: Reduces and spreads out the number of points where vehicles, pedestrians and bicyclists may cross paths.
• Increased efficiency: Separating traffic flow on major street allows the intersection to handle a greater volume of traffic and operate with less delay.
• Better synchronization: Corridor travel times are improved on both the major and side streets through synchronization of the two signalized intersections.
• Shorter wait times: Fewer traffic signal phases means less time stopping at the intersections.

How to navigate

Below shows how to navigate a split intersection. View a larger version.

What is a thru-cut?

• Intersection design where side street through movements are prohibited.
• Side street motorists turn left or right and make another turn at an existing opening to cross the major street.
• Side street left and right turn lanes may be channelized using physical barriers or pavement markings.
• Main intersection may be controlled with a traffic signal, stop signs or yield signs.

When should it be considered?

• On median-divided highways.
• At intersections with low side street through traffic volumes.
• At intersections with heavy major street through and/or left-turn traffic volumes.
• At intersections where side street through movements can be accommodated by rerouting to existing intersections or median openings.
• At intersections with four legs.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths.
• Increased efficiency: Eliminates the side street through movements, allowing for fewer or shorter traffic signal phases, which reduces delay and increases capacity.
• Shorter wait times: Fewer traffic signal phases means less time stopped at the intersection.
• Cost effective: A thru-cut may be more cost-effective than adding lanes to improve capacity.

How to navigate

Below shows how to navigate a thru-cut intersection. View a larger version.

What is a contraflow left?

• A grade-separated interchange where left-turn traffic on the arterial crosses opposing left-turn traffic via channelized lanes.
• Left turns onto the freeway ramps in both directions are made during the same signal phase.
• The roundabouts can have two to four legs.
• Can be designed as an overpass or an underpass.

When should it be considered?

• With limited right of way to add opposing left-turn lanes.
• With heavy left-turn traffic volumes onto the freeway ramps.
• Where there is limited roadway width for left-turn lanes between the ramp intersections and limited right of way to expand or to construct loops.

Benefits

• Improved safety: Vehicles waiting to turn left onto freeway are less likely to create a backup, reducing the potential for rear-end crashes.
• Increased efficiency: Operates with three traffic signal phases rather than four phases, reducing overall interchange delay.
• Better traffic flow: Provides additional space for left-turn traffic waiting to enter freeway, reducing congestion.
• Cost effective: Less space is required between ramps, so the interchange can have a shorter bridge span, potentially reducing costs.

How to navigate

Below shows how to navigate a contraflow left interchange. View a larger version.

What is a DLT interchange?

• Design where left-turn vehicles cross to the other side of the opposing through traffic in advance of the freeway ramps.
• Protected left turns and opposing through movements occur simultaneously at the two ramp intersections.
• Ramp intersections and crossovers are signalized and timed to work together to minimize stops.
• Can be designed as an overpass or an underpass.

When should it be considered?

• With heavy through traffic volumes in both directions of the arterial roadway.
• With moderate to heavy left-turn traffic volumes onto the freeway ramps.
• With low to moderate left-turn traffic volumes onto the arterial from the freeway.
• With limited bridge width, but with right of way available approaching the bridge.

Benefits

• Improved safety: Spreads out the number of potential conflict points where vehicles may cross paths.
• Increased efficiency: Simultaneous movement of protected left turns and opposing through movements allows for only two traffic signal phases rather than the typical four, which reduces delay.
• Better synchronization: Corridor travel times are improved through elimination of left-turn traffic signal phases and synchronization of the ramp intersections and crossover traffic signals, allowing through traffic to spend less time stopped.

How to navigate

Below shows how to navigate a DLT interchange. View a larger version.

What is a DDI?

• A grade-separated interchange design where arterial (a major route that carries traffic between highways and smaller routes) traffic crosses to the other side of the roadway between the freeway ramps.
• Vehicles can turn left onto and off freeway ramps without stopping or crossing opposing lanes of traffic.
• Right turns on and off the freeway ramps occur either before or after the crossover intersections, when traffic is on the “correct” side of the road.
• Both crossover intersections are signalized.
• Interchange can be designed as an overpass or underpass.

When should it be considered?

At locations:

• With heavy left-turn traffic volumes onto and off the freeway ramps.
• Without adjacent traffic signals or nearby driveways.
• Where there is limited roadway width for left-turn lanes between ramp intersections and limited right-of-way to expand.

Benefits

• Improved safety: Reduces the number of points where vehicles may cross paths.
• Increased efficiency: Crossovers can operate with only two traffic signal phases, which allows the interchange to handle a greater volume of traffic and operate with fewer delays.
• Easier access to freeway: Design allows traffic to enter and exit the freeway without crossing opposing lanes of traffic.
• Cost effective: Since there are no left-turn lanes on the arterial, a DDI can have a narrower cross section and may be more cost effective than a retrofit or new interchange construction.

How to navigate

Below is how to navigate a DDI. View a larger version or watch the video.

What is a double roundabout?

• A design where all freeway ramps begin or end at one of two roundabouts.
• The roundabouts are circular, unsignalized interchanges where traffic moves in a counterclockwise direction around a central island.

When should it be considered?

• With heavy left-turn volumes onto the freeway ramps.
• Where there is limited room between the ramp intersections for vehicles to wait at traffic signals.
• At heavily used off-ramp interchanges where vehicles tend to back up on the freeway.

Benefits

• Improved safety: Reduces the number of points where vehicles can cross paths and eliminates the potential for right-angle and head-on crashes.
• Increased efficiency: Decreases the delay for ramp traffic and eliminates signal coordination between the two ramp terminals.
• Continuous flow: Yield-controlled design minimizes backups on the freeway, reducing the potential for high-speed, rear-end crashes.
• Cost effective: Allows for a narrower bridge as it eliminates at least two turning lanes.

How to navigate

Below shows how to navigate a double roundabout interchange.  View a larger version or watch the video.

What is a MUD?

• A grade-separated interchange where left-turning motorists make a U-turn at an adjacent crossover to complete the desired movement.
• The crossovers are parallel to the arterial and are accessed from one-way frontage roads adjacent to the freeway.
• No left turns are permitted at the main intersection.
• Can be signalized, stop controlled, or yield controlled.

When should it be considered?

• With moderate to heavy through traffic volumes and low to moderate left-turn traffic volumes.
• With existing frontage roads.
• Where access to properties and businesses adjacent to the freeway is important.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths and decreases the potential for angle crashes.
• Increased efficiency: Eliminates left-turn movements from the main intersection, allowing fewer traffic signal phases, which reduces delay and increases capacity.
• Better synchronization: Fewer traffic signal phases means less time stopped at the main intersection.

How to navigate

Below shows how to navigate a MUD interchange. View a larger version.

What is a SPUI?

• A grade-separated interchange design where all freeway ramps begin or end at a single signalized intersection on the arterial.
• Right-turn movements onto and off freeway ramps are made at unsignalized intersections separate from the main intersection.
• Interchange can be designed as an overpass or underpass.

When should it be considered?

At locations:

• With limited right of way.
• With heavy left-turn traffic volumes onto and off the interstate or primary road ramps.
• With space to accommodate wider intersection and structure widths.

Benefits

• Improved safety: With only one signalized intersection rather than two at a conventional diamond interchange, vehicles only cross paths at one location.
• Increased efficiency: Main intersection operates with three traffic signal phases rather than four phases in a conventional diamond interchange, which reduces overall interchange delay.
• Increased capacity: Design allows left turns to be made at higher speeds, which increases the capacity of the main intersection.
• Fewer traffic signals: A single signalized intersection, rather than two intersections at a conventional diamond interchange, improves travel times on the arterial.

How to navigate

The image below shows how to navigate a SPUI. View a larger version or watch the video.

What is a single roundabout interchange?

• A grade-separated interchange where all ramps begin or end at a single roundabout on the arterial.
• Serves as the overpass or underpass of a freeway.
• A circular unsignalized intersection where traffic flows in one direction around a central island. Traffic entering the roundabout must yield to traffic already inside.
• Can accommodate more than four intersecting roadways.

When should it be considered?

• With heavy turning volumes onto and off of the freeway ramps.
• In urban areas with moderate traffic volumes.
• Where right of way is limited.
• At heavily used freeway off-ramps where vehicles tend to back up onto the freeway.

Benefits

• Improved safety: Reduces the number of points where vehicles cross paths and eliminates the potential for right-angle and head-on crashes.
• Increased efficiency: Decreases the delay for ramp traffic and eliminates the need for traffic signals.
• Continuous flow: Yield-controlled design minimizes backups on the freeway, reducing the potential for high-speed rear-end crashes.

How to navigate

Below shows how to navigate a single roundabout interchange. View a larger version.