The cloverleaf interchange is one of the attractive innovations in civil engineering. A cloverleaf interchange is a two-level interchange at which left turns are done by ramp roads (reverse directions in left-driving regions). It is not only aesthetically pleasing but also provides several advantages to the transportation system.

We will go through the main details in the blog.

Let’s start from scratch.

1. What is cloverleaf interchange ?
2. Examples of cloverleaf interchange in India
3. Cloverleaf interchanges – Main problems and challenges
4. Upgrades for cloverleaf interchanges
5. Traffic signals in leu of cloverleaf interchange

What is cloverleaf interchange ?

• A cloverleaf interchange is a two-level interchange at which left turns are done by ramp roads (reverse directions in left-driving regions).
• Vehicles first proceed to go left (in right-hand traffic) as one lane crosses over or below the other. Then, exit right onto a one-way three-fourth loop ramp (270 °) and merge onto the intersecting road.
• The purpose of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by red lights, except for the left and right turns.
• Traffic weaving is the limiting factor in a cloverleaf interchange’s ability.

In the next section, let me take you through some examples of clover leaf in India.

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Examples of cloverleaf interchange in India

1. Kathipara Cloverleaf, Chennai
2. Maduravoyal Cloverleaf, Chennai
3. Koyambedu Cloverleaf, Chennai
4. Badarpur Cloverleaf, Delhi
5. Yamuna Cloverleaf-Noida
6. Mukarba Chowk Cloverleaf, Delhi
7. BMIC Cloverleaf, Karnataka

Also read: Road pavement structure-Components and functions

So, you got an idea about clover leaf roads. Let me quickly walk you through the major challenges and problems associated with this.

Cloverleaf interchanges – Main problems and challenges

• The biggest downside of the cloverleaf’s classic configuration is that at the end of a loop, vehicles converge on the highway immediately before other vehicles exit to go around another loop, causing a dispute known as weaving.
• Weaving restricts the number of traffic-turning lanes.
• Since then, the majority of road authorities have adopted new interchange designs with less-curved exit ramps which do not lead to weaving.
• These interchanges include diamond, parclo and single-point urban interchanges (SPUI) when connecting at the crossroads to an arterial road in non-free-flowing traffic and the stack or clover and stack hybrids when connecting in free-flowing traffic to another freeway or to a busy arterial where signals are not yet needed.

Upgrades for cloverleaf interchanges

• For new interchanges, not only are these ideas valid, but they also hold when existing cloverleaf interchanges are upgraded.
• The exchange between US 13 and US 58 was originally a cloverleaf in Norfolk, Virginia; it has since been turned into a SPUI.
• In addition, several cloverleaf interchanges are being upgraded to parclos on California freeways, such as U.S. 101. In Hampton, Virginia, a cloverleaf interchange was partly unwound into a partial stack interchange between Interstate 64 and Mercury Boulevard.
• As part of a major highway improvement project to upgrade the highway to Interstate standards, four cloverleaf interchanges along I-64/US 40 in St. Louis, Missouri, were substituted with SPUIs between 2008 and 2009.
• Adding a collector/distributor route next to the highway is a compromise; this does not prevent weaving but takes it off the main lanes of the freeway. An example of this is the Sheboygan, Wisconsin, State Highway 23/Interstate 43 interchange, where the exit/entrance roads on and off Highway 23 are two lanes on the north and southbound sides of the road next to the main I-43 freeway.

Traffic signals in leu of cloverleaf interchange

• Several cloverleaf interchanges on the non-freeway route have been removed by installing traffic signals.
• This is also done sometimes at the intersection of two freeways, particularly when one freeway ends at an interchange with another.
• An example of this is at the intersection between Interstate 5 and Washington State Route 512 in Lakewood, Washington, where a noticeable ramp stub reveals that one of the four leaves has been cut, thus removing weaving on I-5.
• The traffic signal will be replaced by a two-lane flyover in the future, again completing the freeway-to-freeway interchange.
• Cloverleaf exchanges often appear to consume much more land than any other form of exchange (with the possible exception of stack interchanges).
• Numerous cloverleaf intersections include the merging of traffic from the clover directly into the collector/distributor lane in the Lower Mainland of British Columbia, Canada.
• This allows the slowly moving driver to merge around the loop ramp with the rapidly moving driver leaving the collector/distributor lane without the ability to accelerate to balance the oncoming driver’s flow.
• This merging velocity gap can be as high as 65 km/h (approx. 43 mph).
• In the United Kingdom, owing to these performance concerns, the cloverleaf interchange was not introduced in significant numbers. Originally, there were three, one in Redditch and two in Livingston.
• In Ontario, most cloverleaf interchanges have been phased out, but with similar traffic patterns, some near variants remain.
• However, the key difference is that single bidirectional carriageways share the adjacent on and off-ramps.
• Examples include the intersection in Belleville, Ontario, between Highway 62 and Highway 401, as well as the interchange in Toronto between Lawrence Avenue and Don Valley Parkway.

So, how was the trip through the clover leaf interchange? Let me know in comments, if you have any queries.