Cloverleafs & Traffic

Imagine you're driving down your local highway when you come to a stop. What is this traffic?, you think. Then you look ahead and see a cloverleaf interchange. Cloverleafs are a type of cheap, low-traffic tolerance interchange. It's so cheap that it only has two sets of bridges—which are way more expensive than regular, ground level roads—versus a traditional free-flowing (or no stops), four-way interchange. Although, cloverleafs are cheap compared to other interchanges they cannot handle high levels of traffic.

How Were Cloverleafs made?

Cloverleafs were created by civil engineer Arthur Hale during 1915, who patented the interchange. The first one was built in 1928 in Woodbridge, New Jersey. Although, it has since been replaced with a partial cloverleaf interchange. 

The first cloverleaf west of the Mississippi River debuted on August 20, 1931.

However, the first cloverleaf interchange in Canada opened in 1937. 

The cloverleaf was patented in Europe, Switzerland on October 15, 1928. The first cloverleaf in Europe opened in October 1935 at Slussen in central Stockholm.

How Cloverleafs Work?

How the cloverleaf works is by having these slip roads to turn right (see in picture). Then to turn left you continue straight through the overlap of highways. After that, turn right on an offramp. Lastly, while on that offramp you loop all the way around to go onto the left side of the other highway.

Why can't Cloverleafs handle large amount of traffic?

Cloverleafs are cheap, although, too much traffic can cause problems. First, traffic enters coming off a loop and goes to your highway. Then, traffic trying to turn left—using the loop—has to cut to the right, while traffic just coming on has to cut onto the highway. 

This means that there is three different traffic routes on one road merging simultaneously: traffic going straight, traffic turning left of the loop, and traffic going straight that just merged with the road. So, cars slow down to be able to weave in between lanes. This problem creates conflict points which can create traffic for roads.

Glossary

Interchange—a road junction designed on several levels so that traffic streams do not intersect.

Slip Roads—a short road used to join or leave a major road, like a freeway or highway, without direct entry or exiting the main traffic.

Offramp—a one-way road leading off the main highway.

Interchange—a road junction designed on several levels so that traffic streams do not intersect.

Slip Roads—a short road used to join or leave a major road, like a freeway or highway, without direct entry or exiting the main traffic.

Offramp—a one-way road leading off the main highway.