A single roundabout can save 80,000 liters of fuel, making roundabouts a new trend of emission reduction in Europe and America. Why are they not very suitable for Chinese cities?

In the state of Indiana, United States, there is a city renowned for its traffic roundabouts: Carmel.

This small city, with a population of just over 100,000, boasts approximately 160 roundabouts, averaging one for every 600+ residents. It is no wonder it is called the "Roundabout Capital of America." If you openly express your hatred for roundabouts here, be careful—you are very likely to draw criticism and dissatisfaction from local residents.

As of August 2025, Carmel had a total of 158 completed roundabouts | Carmel City Hall

While it may sound a bit odd, Carmel's obsession with roundabouts does not stem from some strange collective fetish, but from a focus on safety and environmental protection. Especially at a time when atmospheric warming is accelerating and extreme weather is becoming more frequent, an increasing number of cities are beginning to follow Carmel's example, taking "building roundabouts" as a new way to combat climate change.

It should be noted that the roundabouts in Carmel are not the large-scale roundabouts or circular intersections commonly seen elsewhere. Locals prefer to call them "modern roundabouts."

A roundabout intersection in Carmel | Indiana University

Large-scale roundabouts or circular intersections are usually very huge, with multiple lanes, complex traffic flow lines, and countless traffic lights. Moreover, vehicles often enter the roundabout at a 90-degree "perpendicular" angle, making side collisions extremely likely.

The "modern roundabout" (hereinafter referred to as a roundabout) is much smaller in area, with fewer lanes, lower speed limits, and no traffic lights. In addition, the angle between the lane and the circular ring when entering the roundabout is very small, which can greatly reduce the probability of serious side collisions.

This is one major reason why Carmel actively embraces roundabouts: safety.

At a circular intersection (left), side roads often merge into the roundabout at 90 degrees, making serious side collisions prone to occur

Large roundabouts (left) have more lanes and relatively complex traffic flow lines | All About Roundabouts

A survey conducted by the Insurance Institute for Highway Safety found that at 64 intersections in Carmel that were converted to roundabouts, the number of injury accidents dropped by about 50% compared to traditional crossroads. In a more uniquely shaped "dogbone" roundabout, this reduction was even more significant.

The fatality rate from traffic accidents in Carmel is also remarkably low. For example, in 2020, 1.9 people per 100,000 residents in Carmel died in traffic accidents, compared to 20.8 in Indianapolis, the capital of Indiana, and 11 across the United States as a whole.

Previously, vehicles exiting the highway had to wait for two red lights to turn left across the highway. Engineers then replaced the traffic lights with two roundabouts, forming a dogbone shape | North County Pipeline

Another major advantage of roundabouts is environmental friendliness.

Since Carmel's "modern roundabouts" have no signal lights, vehicles do not need to idle and burn fuel while waiting for red lights, which means fewer exhaust emissions. Moreover, simply removing the traffic lights from 160 intersections can save a considerable amount of electricity and reduce local government maintenance costs.

The Carmel government estimates that roundabouts can reduce carbon emissions at each intersection by 16% to 59%, which on average is equivalent to saving 76,000 liters of gasoline per intersection per year. The reduction in exhaust emissions has even improved air quality in some areas, with a particularly noticeable drop in nitrogen oxide levels.

The circular intersection at Old Meridian Street and Pennsylvania Street features a 13-meter-tall flower sculpture | Online

Today, roundabouts have even become a cultural symbol of Carmel. You can not only buy related books (such as *Carmel Roundabouts: The Best Works from 1997 to 2010* and *Roundabouts Done Right*), but also find a roundabout-themed cultural and creative store—and the main street in front of that store has 11 roundabouts.

A unique "Roundabout Gallery" culture has also taken root here: one roundabout has a racing car sculpture built by artists with lines in its center, and another roundabout has a steel flower standing tall at its core. The roundabout at the intersection of Main Street and Guilford Road is even decorated with elegant boxwood hedges and a three-tiered bronze fountain made in France, earning it the title of Carmel's "epitome of elegance."

Online

Where some people love roundabouts, there are bound to be others who hate them.

One resident complained that out-of-town vehicles often get stuck in roundabouts because they are unfamiliar with the rules, causing congestion. Another resident said that when you are in a good mood, roundabouts seem fine, but if you are in a bad mood and get stuck in traffic, the roundabout will become the "scapegoat."

In 2019, Carmel's roundabouts faced their biggest public reputation crisis. The *Indianapolis Star* published an article stating that after embracing roundabouts, Carmel's accident rate actually rose instead of falling. In response, then-mayor James Brainard refuted that the statistical base of the *Star* was incorrect, because during his 28 years in office, Carmel's permanent resident population quadrupled, and there was also a large amount of out-of-town traffic during the day.

A roundabout sculpture named "Sunrise". A netizen commented: The artist might not be able to keep up with the construction speed of roundabouts | Reddit

Andrea Bill, director of the Traffic Operations and Safety Laboratory at the University of Wisconsin-Madison, admitted frankly that roundabouts do sometimes increase the probability of minor vehicle collisions, but they can indeed greatly reduce the probability of serious traffic accidents.

"It's a bit like the difference between needing a tow truck and needing an ambulance," she said.

To promote the rules of roundabouts, the Carmel government has produced a lot of promotional materials | Carmel

"Modern roundabouts" also have a major limitation: they are almost only suitable for suburban cities like Carmel. These cities have moderate traffic volumes, few pedestrians, and relatively even traffic flows in all directions at intersections, making it easy for drivers to find gaps to enter the roundabout.

However, in large cities like New York or Beijing, the traffic flow in each direction at intersections can be more than ten times that of Carmel. This would cause vehicles on main roads to continuously pile up inside the roundabout, while vehicles on side roads would have no chance to enter at all. Coupled with the large number of pedestrians in big cities, the area around the roundabout could also become completely chaotic.

In some cities, roundabouts may make road conditions worse | Online

But for now, it seems that Carmel has no intention of abandoning roundabouts. At present, there are still two roundabouts under construction in the city, and the remaining traditional signal-controlled crossroads number no more than 8 at most.

References:

[1]https://www.nytimes.com/2021/11/20/climate/roundabouts-climate-emissions-driving.html

[2]https://www.mympo.org/blog/all-about-roundabouts?tmpl=component&print=1&format=print

[3]https://www.forbes.com/sites/marshallshepherd/2023/02/17/will-traffic-roundabouts-save-us-from-climate-change/

This article is from the WeChat official account "Bringing Science Home" (ID: steamforkids), written by Liu Liuqisi, reviewed by A Xian, and published with authorization by 36Kr.