Road Junctions - Transportation Planning

Road Junctions and Grade Separators for Transportation Planning - A Junction is an area, where two or more roads join or cross, whose main function is to provide for the change of route directions.
Grade separation is a method developed to avoid the disruption of traffic flow at intersections. It is adopted at junctions where two or more surface transport axes cross with each other.
Grade separation is generally achieved by means of a vertical level.

1. ROAD JUNCTIONS GRADE SEPARATORS LOOP INTERCHANGE UNDERPASS TRANSPORTATION PLANNING SUBMITTED BY : SUBMITTED TO : Prachi Kothary – 6 Akshata Parbate - 10 Prof. Kishore Joglekar

2. ROAD JUNCTIONS A Junction is an area, where two or more roads join or cross, whose main function is to provide for the change of route directions. 2 2 Since the main function of an intersection is to enable the road user to make a route choice, it is a point of decision. Hence the problems that are encountered by the motorist while passing through an intersection must be recognized and the design should be in such a way that the driving task is as simple as possible. Junctions tend to have a high potential for crashes. COMPLEX JUNCTION SIMPLE JUNCTION ROAD JUNCTIONS O nly two roads crossing at a right angle T hree or more roads cross within the same area

3. TYPES OF INTERSECTIONS Intersections are classified into two broad categories: 3 3 GRADE SEPARATED INTERSECTION INTERSECTIONS INTERSECTION AT GRADE It is a bridge that eliminates crossing conflicts at intersections by vertical separation of roadways in space. Route transfer at grade separations is accommodated by interchange facilities consisting of ramps. An intersection is a junction where two or  more roads meet or cross.  Roads that cross each other at the same level or elevation are called At Grade Intersections. 

4. KEY ELEMENTS OF ROAD INTERSECTIONS Intersection legs are those segments of roadway connecting to the intersection. The leg used by traffic approaching the intersection is the approach leg, and that used by traffic leaving is the departure leg. Africa Asia INTERSECTION LEGS Africa Asia Sidewalks, crosswalks, and pedestrian curb-cut ramps are considered to be within the intersection. The pavement edge corner is the curve connecting the edges of the pavement of the intersecting streets. Channelizing and divisional islands may be added to an intersection to help delineate the area in which vehicles can operate and to separate conflicting movements. A turning roadway is a short segment of a roadway for a right turn, delineated by channelizing islands. Traffic control devices assign right of way, to both motorized and non‐motorized traffic and include traffic signals, pavement markings, STOP signs, YIELD signs, pedestrian signal heads and other devices. SIDEWALKS | CROSSWALKS ISLANDS TURNING ROADWAY TRAFFIC CONTROL DEVICES 4 4 The key elements of Road Intersections can be classified as follows :

5. INTERSECTIONS AT GRADE Lorem ipsum dolor sit amet , consectetur adipiscing elit . THREE LEG INTERSECTIONS STAGGERED 4 LEG INTERSECTIONS ALIGNED 4 LEG INTERSECTION MULTI-LEG INTERSECTION 5 5 T- Junction Skewed Junction Y - Jun ction Staggered Junction Staggered–Skewed Intersection Cross Intersection Cross - Skewed Intersection 5 - Leg Intersection 6 - Leg Intersection Intersections at Grade are broadly classified into the following basic forms :

6. T - JUNCTION 6 6 Y - JUNCTION T intersections work well in low and medium volumes of traffic but can be difficult to emerge from when turning right if traffic is heavy. The T-intersection must have traffic lights installed to control when vehicles can go. When a stop sign is placed at a T-intersection it is usually because visibility of the road is restricted as you approach it. It is pretty useful in the distribution of traffic. To provide two options for vehicles traveling on the main road . A T-junction has three arms of which one arm is a main road whereas the other one is usually a minor road connecting the main road. A Y-junction has three arms of which all three roads are of equal sizes. It is generally seen in places of heavy traffic.

7. 7 7 CROSS JUNCTION SKEWED -CROSS JUNCTION Skewed cross junctions are often used when the existing road layout or geographical constraints make it impractical to have a standard perpendicular intersection. This design helps to optimize space and improve traffic flow. They can result in longer crossing distances for pedestrians and facilitate higher-speed turning movements by vehicles. A four-way intersection , also known as a crossroads, is where two roads intersect each other at right angles, forming a four-way junction. The purpose of Cross Junctions is to facilitate the crossing of two perpendicular roads, allowing vehicles to change their direction of travel. Crossroads are often used in urban and suburban areas and can handle moderate to high traffic volumes. Proper signalization and signage are crucial for managing traffic efficiently. A skewed cross-intersection is similar to a crossroads, but the roads do not intersect at right angles; they are skewed or angled.

8. 8 8 STAGGERED JUNCTION SKEWED & STAGGERED JUNCTION Typically, a minor road will meet a major road and continue onto a minor road slightly further ahead.  Major single-point traffic-light controlled junctions of more than two roads are often reconfigured into staggered junctions in order to increase traffic flow through them. They are often used instead of a standard crossroad in busy areas.  A skewed and staggered junction is a combination of staggered and skewed junctions where both the offset and the non-right-angle elements are present. A  staggered junction  is a place where several roads meet a main road at a slight distance apart thus they do not all come together at the same point. Purpose: This type of junction is often used in complex urban environments where space constraints and irregular road layouts necessitate a combination of skewed and staggered features to optimize traffic flow and safety. Design: The design involves careful planning of the angle of intersection and the staggered layout, taking into consideration traffic volume, turning movements, and pedestrian crossings.

9. 9 9 MULTI – LEG JUNCTION SKEWED JUNCTION A multi-leg junction refers to an intersection with three or more roads converging at a single point. Purpose: Multi-leg junctions are common in urban areas with complex road networks. They are designed to efficiently manage the flow of traffic from multiple directions, including left and right turns. Design: The design of a multi-leg junction involves considerations for traffic signals, turning lanes, pedestrian crossings, and other features to ensure the safe and smooth movement of vehicles from different directions. This type of junction can be challenging for drivers because of the skewed angle, which may require them to make sharper turns or have limited visibility of oncoming traffic. Warning signs are meant to improve safety by providing advance notice to drivers and allowing them to adjust their speed and approach accordingly. A skewed side road junction refers to a road intersection where one road meets another at an angle instead of a typical perpendicular intersection.

10. ROTARIES / ROUNDABOUT INTERSECTIONS Lorem ipsum dolor sit amet , consectetur adipiscing elit . 10 10 Rotary intersections or roundabouts are special forms of at-grade intersections laid out for the movement of Traffic in one direction around a central traffic island. Essentially all the major conflicts at an intersection namely the collision between through and right-turn movements are converted into milder conflicts namely merging and diverging. Traffic flow is regulated to only one direction of movement, thus eliminating severe conflicts between crossing movements. All the vehicles entering the rotary are gently forced to reduce the speed and continue to move at a slower speed. Because of the lower speed of negotiation and elimination of severe conflicts, accidents, and their severity are much less in rotaries . Rotaries are self-governing and do not need practically any control by police or traffic signals. They are ideally suited for moderate traffic, especially with irregular geometry, or intersections with more than three or four approaches. ADVANTAGES OF ROTARY Three types of conflicts when traffic streams interfere with each other: Merging Diverging Crossing

11. Diverging : It is a traffic operation when the vehicles moving in one direction is separated into different streams according to their destinations. Merging : Merging is the opposite of diverging. Merging is referred to as the process of joining the traffic coming from different approaches and going to a common destination into a single stream. Weaving : Weaving is the combined movement of both merging and diverging movements in the same direction. T hese movements are shown in figure. It can be observed that movements from each direction split into three; left, straight, and right turn. DESIGN OF ROTARY DESIGN ELEMENTS OF ROTARY Desi gn elements include design speed ; entry, exit and central island radius; width of rotary; weaving length and width ; entry and exit widths. TRAFFIC OPERATIONS IN ROTARY

12. ADVANTAGES OF GRADE SEPARATION Grade separation eliminates the stopping of vehicles while crossing the roads. It provides safety and reduces the risk of accidents . Speed limits for grade-separated roads are generally higher hence, high speeds can be maintained at intersections which results in saving of travel time. Grade separation can be provided for all likely angles of any two intersecting roads. Grade separation is a method developed to avoid the disruption of traffic flow at intersections. It is adopted at junctions where two or more surface transport axes cross with each other. Grade separation is generally achieved by means of a vertical level. 12 12 The ultimate objective of grade-separated intersections (interchanges) is to eliminate all grade-crossing conflicts and to accommodate other intersecting maneuvers by merging, diverging, and weaving at low relative speed . GRADE-SEPERATORS

13. An overpass also known as a flyover , is a bridge, road, railway, or similar structure that crosses over another road or railway. A pedestrian overpass allows pedestrians to cross over busy roads without impacting traffic. An underpass or a tunnel is an underground passageway, completely enclosed except for openings for ingress and egress, commonly at each end. A tunnel may be for foot or vehicular road traffic, for rail traffic, etc. GRADE SEPARATION CAN BE ACHIEVED BY TWO INTERSECTIONS OVERPASS UNDERPASS 13 13

14. Grade separation eliminates intersection of traffic flow at junctions but it is incomplete without provision for interchanges. Interchanges facilitate the change of direction of traffic from one highway to another highway at intersections. Interchange ramps at grade separations can be provided in three different types and they are : INTERCHANGE DIRECT SEMI-DIRECT INDIRECT 14 14 MAJOR INTERCHANGES Trumpet Interchange Diamond Interchange Cloverleaf Interchange Partial Cloverleaf Interchange Directional Interchange Stack Interchange Rotary Interchange

15. KEY ELEMENTS OF INTERCHANGE These are additional lanes on the main road specifically designated for vehicles entering or exiting the interchange. Africa Asia ENTRY / EXIT LEGS Lorem ipsum dolor sit amet , consectetur adipiscing elit . Africa Asia These are inclined or curved sections of road that connect the main road to the interchange. They can be on-ramps (for entering the interchange) or off-ramps (for exiting the interchange). Bridges that allow one road to pass over another to eliminate intersections and facilitate continuous traffic flow. Distributor lanes or roads help manage local traffic within the interchange, providing access to different ramps and facilitating smoother transitions. A positive line is often painted on the road surface to indicate the correct path for vehicles to follow, helping to prevent lane drifting and ensuring smooth traffic flow. RAMPS OVERPASS DISTRIBUTOR LANE POSITIVE LINE 15 15 15 15 The key elements of Interchange can be classified as follows :

16. Ramps and Loops: Cloverleaf interchanges consist of a series of ramps and loops that connect the intersecting highways. These ramps form a pattern that allows vehicles to enter and exit the highways in a smooth and efficient manner. Loop Ramps: The loop ramps in a cloverleaf interchange are typically used for making left turns or U-turns . These ramps are designed to loop around and pass over or under the intersecting highways, allowing vehicles to change direction. Cloverleaf interchanges contain 4 legs and eight ramps. Cloverleaf interchanges are used at intersections where two major highways cross each other. The objective of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by red lights , even for the left and right turns. Kathipara, Chennai 16 16 CLOVER LEAF INTERCHANGE A  junction  of two  highways , one  crossing  over the other, having a  series  of  exit  and  entrance   ramps , arranged in the form of a four-leaf  clover , such that  traffic  may proceed from either  highway  in all  directions .

17. Trumpet interchanges have been used where one highway terminates at another highway. These involve at least one loop ramp connecting traffic either entering or leaving the terminating expressway with the far lanes of the continuous highway. A trumpet interchange is a type of road junction that features a loop ramp that turns 270 degrees, resembling the shape of a trumpet. It is often used when one road crosses over another but there is not enough space or the terrain is not suitable for a full cloverleaf interchange. Jamnagar-Amritsar Express highway 17 17 A  Trumpet interchange is a road junction that typically uses grade separation, and one or more looped ramps, to permit traffic on at least one highway to pass through the junction without directly crossing any other traffic stream. TRUMPET INTERCHANGE

18. 18 18 Two level semi-directional T interchange in  Orbe, Switzerland . DIRECTIONAL INTERCHANGE A directional interchange refers to a type of highway interchange designed to facilitate the movement of traffic between two major roads or highways in a specific direction. It allows vehicles to transition from one road to another in a smooth and efficient manner. Directional interchanges are typically used in areas where two highways intersect, and they aim to minimize disruptions to the flow of traffic. Directional interchanges are generally preferred where two high-volume freeways intersect. They reduce travel distance, increase ramp speed and capacity, and eliminate weaving movements. Since traffic movements between the two freeways are free-flow with this interchange configuration, at-grade intersections are eliminated, only direct ramp connections from one freeway to the other.

19. The  High Five  in  Dallas, Texas . This is a complicated five-level stack interchange, due to the proximity of  frontage roads  and segregated high-occupancy vehicle lanes. This hybrid design is based on parts of a four-level stack for highways, with a three-level-diamond interchange to handle the frontage roads. 19 19 A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two access-controlled highways that allows free entry and exit for traffic in all directions. These interchanges eliminate weaving problems, have the highest vehicle capacity, and offer shorter vehicle travel distances compared to other types of interchanges. The first directional interchange built in the world was the Four Level Interchange, which opened to Los Angeles Transit in 1949 . STACK INTERCHANGE

20. The first DI in Washington State was built at the Interstate 5 and State Route 510 (Marvin Rd) interchange in Lacey, WA. 20 20 A  diamond interchange is a common type of  road junction , used where a  controlled-access highway  crosses a minor road. Visual showing how diamond interchanges are used, with an expressway running across and a local road running in the center. The freeway itself is  grade-separated  from the minor road, one crossing the other over a  bridge . Approaching the  interchange  from either direction, an off-ramp diverges only slightly from the freeway and runs directly across the minor road, becoming an on-ramp that returns to the freeway in similar fashion. DIAMOND INTERCHANGE

21. Highway 407 Electronic Toll Route  in Ontario 21 21 PARTIAL CLOVERLEAF Partial cloverleaf is a modification that combines some elements of a diamond interchange with one or more loops of a cloverleaf to eliminate only the more critical turning conflicts. It provides more acceleration and deceleration space on the freeway. The Diamond Interchange has four ramps. The Cloverleaf Interchange has eight ramps like the Stack Interchange. Unlike Parclos, it is completely sterically separated and traffic flows without stopping on all ramps and main roads. Parclos usually have 4 or 6 ramps, but rarely 5 ramps. Partial cloverleaf interchanges are often used in situations where a full cloverleaf interchange is not feasible due to space constraints, cost considerations, or other limitations . They provide a balance between the efficiency of a cloverleaf design and the constraints of the surrounding environment.

22. An overpass also known as a flyover, is a bridge, road, railway or similar structure that crosses over another road or railway. A pedestrian overpass allows pedestrians safe crossing over busy roads without impacting traffic. 22 22 ROTARY INTERCHANGE A Rotary interchange is typical to enter a rotary alongside traffic that is circulating in the inside lanes, like a freeway cloverleaf loop entrance where the ramp entrance lane continues under or over a bridge to the next exit. A rotary interchange, also known as a roundabout or traffic circle, is a type of road junction in which traffic moves in one direction around a central island. In a rotary interchange, vehicles enter the circle at various points and navigate around it until they reach their desired exit, which could be a specific road leading away from the circle. The circular design helps to eliminate the need for traffic signals and allows for a more continuous flow of vehicles. Drivers entering a rotary interchange must yield to the circulating traffic before merging into the circle. Rotary interchanges are common in many countries around the world and are considered an effective traffic management solution when designed and implemented appropriately. Rotary interchange in Italy .

23. CONCLUSION 23 23 In closing, the intricate dance of roads converging at a junction symbolizes the interconnected pathways of our transportation networks. Navigating through these intersections requires a harmonious blend of careful planning , innovative design , and advanced technology . As we conclude our exploration of road junctions, let us remember that these intersections serve as the crossroads of progress, enabling the smooth flow of people and goods, fostering economic growth , and connecting communities . Just as roads converge at a junction, so do the various elements of urban planning , engineering , and technology converge to create a safer, more efficient, and sustainable transportation infrastructure. Let us continue to invest in the future of road design, embracing new ideas and solutions that pave the way for a connected and vibrant world.

24. THANK YOU!