Driving along a motorway or freeway, you must have seen gigantic highway interchanges sprawled in a huge area. So, what is a highway interchange? What are the purpose and their types?
Please read this blog for details:
What is the Highway Interchange?
Highway Interchanges are basically road junctions, but they are constructed at grade-separated levels. This allows traffic to change the direction of travel through a junction and join the next motorway or freeway without compromising the driving speed. On the contrary, urban road junctions are designed to control the movements (via signal control of roundabout) to allow the change in direction of travel.
Highway Interchanges are only recommended when at least one road out of the two is a motorway or freeway. That’s why there are two types of highway interchanges based on their functionality.
- Service Interchanges
- System Interchanges
As the name suggests, service interchange connects a motorway or freeway to secondary roads such as national roads, local roads, etc.
In service Interchanges, it is recommended to provide free flow traffic to the motorway traffic but traffic along the minor road are designed to move at a lower speed. In some cases, when traffic exited the motorway and joins the secondary road, it would require controlling it by the signal control system or compact dumbbell roundabout design.
Following are key types of Service Interchanges:
- Compact Grade Separated Junction
- Dumbbell Roundabout Interchange
- Diamond Interchange
- Half Cloverleaf or Partial Cloverleaf Interchange
Compact Grade Separated Junction
Compact grade-separated junction provides left-in left-out facility to and from a high-speed road and connects it to the low-speed road. The compact grade-separated junction is not recommended to use for motorway junction.
It is preferable to provide a compact grade-separated junction on a high-speed road when central reserve prohibits right turn movement and so junction is used to provide right-turn movement.
Dumbbell Roundabout Interchange
The Dumbbell Roundabout Interchange is a fusion of roundabout interchange and diamond interchange.
It provides more or less the same capacity as roundabout interchange, but it takes far less footprint than that. It economical to build because it only needs one bridge and a lesser footprint means less land acquisition. It can easily be upgraded to a signal-controlled junction if needed.
Diamond Interchange is commonly used on Motorways or Freeways where minor roads are busy road in the urban landscape. In the urban scenario, Diamond Interchange takes lakes far less land than other interchanges. Diamond Interchanges mostly comes with a signal-controlled system to regulate traffic movement.
Half Cloverleaf or Partial Cloverleaf Interchanges
As the name suggests, partial cloverleaf provides one or two or three loops as a diversion left lane from one motorway to the other. These interchanges are commonly used to accommodate very high traffic movements two cross-directional motorways or freeways.
In the urban landscape, where land availability is very restricted, Partial Cloverleaf is a preferred option.
System Interchanges connects two Motorways or Freeways in such a way that all the traffic movements continue without any obstruction or lowering the speed. As a result, the overall size of the interchanges is far bigger than a normal signal-controlled junction or service interchanges.
Following are key types of System Interchanges:
- Full Cloverleaf Interchange
- Three Level Roundabout
- Cloverstack Interchange
- Turbine Interchange
- Windmill Interchange
- Direction Interchange or Y Interchange
- Trumpet Interchange
Full Cloverleaf Interchange
Full Cloverleaf interchange allows a completely free-flow traffic movement between two motorways or freeways. A full Cloverleaf needs significant land to provide all free-flow movement as a result, it is normally recommended in rural motorway to the motorway junction.
Although Full cloverleaf interchange provided free flow movement in all direction, if needed, it can easily be converted to a higher volume direction interchange.
One of the very important disadvantages of a full cloverleaf is the “multiple weaving”. When the driver exit from one diverges, complete a loop and enter to next merge to diverge again to make a U-turn, it opens the significant risk of side by a side vehicle collision. It also induces the significant risk of traffic jams due to numerous merge/ diverge in a short span.
Three Level Roundabout
Three-level roundabout interchange is one of the oldest style highway interchanges. These interchanges are constructed using two bridges to complete a circulatory carriageway connecting all approached at the grade-separated level.
These interchanges provide comparatively a lower junction capacity than other interchanges. Also, entering and exiting from these roundabout interchanges are very confusing for drivers.
In modern infrastructure design, this type of interchanges is not considered a preferred option.
Cloverstack Interchange is one of the most efficient free-flow interchanges that caters all direction movement between motorway to the motorway junction. one of the main advantages of clover stack interchange is that it provides nearly a weaving free movement with minimum construction of the interchange.
Three-level cloverstack interchange is one of the most efficient types of interchanges to connect two high-speed motorways.
Turbine Interchange is a customized version of Stack Interchange with three levels of traffic movement. Turbine interchange is very useful for hilly terrain topography as it comes with numerous merge/ diverge ramps and loops.
As a result, the profile of those loops passes through various crest and valley to suffice all free-flow movement. The hilly terrain helps to minimise the excessive cutting or filling of alignment and reduce the construction cost.
Windmill interchange is very comparable to Turbine Interchange, but it comes with a reduces capacity and speed. As a result, it takes far less land take to compare to a Turbine Interchange.
A very know Windmill Interchange is built-in Netherland in the late seventies known as Vaanplein Interchange.
Direction Interchanges or Y Interchanges
Directional Interchange or Y Interchange are very useful to propose when two motorways or three motorways join at one point at almost right angles.
In this case, a two levels directional interchange, with multiple merges and diverge lanes are developed and there will be no need to provide any loop to suffice a traffic movement. As a result, the land take will be significantly lower than other types of highway interchanges.
Although, its shape does restrict the speed when the straight-ahead moment approach to turn left or right direction with desirable minimum radii. Therefore, these types of interchanges are only recommended for a T- shape interchange situation.
Trumpet Interchanges are one of the oldest forms of highway interchange for a T-junction type situation where one motorway terminates by joining another motorway at a perpendicular angle.
In this case, merge and diverge of the terminating motorway, joins the other motorway via loops and create a shape like a trumpet. These types of junctions are commonly seen when a free flow motorway is intended to join a toll road or motorway, which means when non-toll motorway terminates, and a toll road motorway begins.
Hope this blog helps you understand the definition of an Interchange and also helps you to see the difference among all form of highway Interchange. Please feel free to comment and share.
- Types of Road Pavement in Construction: 6 Important Points
Admin, gcelab.com Please see our Pillar Post to know why we founded gcelab.com.
Founder at gcelab.com, Pooja is an Entrepreneur unlocking human potential. Working in the Principles of Lean Start-up, Pooja believes in Transparency and User Happiness the most. Pooja’s background in teaching gives her a sophisticated grasp on even on the most tedious aspect of course building. She is passionate about people who believe that good is not enough.