In Support of the Humble Roundabout

In 2020, the National Highway Traffic Safety Administration found that 36% of all accidents either occur at intersections or are intersection-related. Furthermore, the Center for Disease Control found that 27% of fatal bicycle accidents occur at intersections; non-intersection accidents have a higher fatality rate because motor vehicle speeds tend to be higher. In any case, roughly a third of all accidents occur in an area in which bicycles and motor vehicles spend much less than a third of their time, so it follows that improving safety at intersections is a top priority.

Roundabouts, also known as traffic circles, are an excellent means of improving safety at intersections. The very nature of a roundabout prevents distracted drivers from proceeding straight through the intersection without noticing the light has changed, and all traffic is forced to reduce speed. Furthermore, roundabouts eliminate some of the most dangerous behaviors commonly found at intersections - 10.3% of all motor vehicle accidents involve turning left, and another 10.7% involve a car stopped in the roadway, an occurrence most frequently found at red lights.

Importantly, roundabouts are much safer for cyclists. Since bike lanes are typically found on the right side of a roadway, it’s easy to incorporate a bike lane into the outermost region of a roundabout. As motor vehicles inside the roundabout approach a cyclist from behind, the cyclist is directly in their line of sight, reducing the chances that a motorist will hit a cyclist that they didn’t notice. Motorists turning into an intersection will also have cyclists in their direct line of sight as they look left to check for any vehicles approaching from inside the roundabout.

At intersections between large, busy streets, another method is to completely separate the bike lane from traffic within the roundabout - just as it is on the roadway. In this scenario, cyclists would have to cross each roadway in the intersection at pedestrian crossings in order to proceed through the roundabout. This is a minor inconvenience for both cyclists and motorists, who now have to stop at a pedestrian crossing far back from the intersection, but the additional safety is worth a five second inconvenience. Far too often, the speed and convenience of motorists is prioritized over the safety of everyone else.

In addition to improved safety, roundabouts are more effective at moving traffic. In an experiment conducted by the popular television series Mythbusters, an experiment concluded that in 15 minutes, a four-way stop could move 460 motor vehicles using a roundabout, 385 vehicles using a stop sign, and 289 using a traffic cop - essentially the equivalent of a stoplight. The key difference is a roundabout is able to accomodate many vehicles in the intersection at the same time, traveling in different dierections.

Notably, the Mythbusters experiment was done with American drivers, the vast majority of which are unaccustomed to roundabouts.

The true limitation to a roadway's capacity isn't the number of lanes - it's the intersections. When intersections are controlled by stoplights, traffic flows all at once in one or two directions, but is almost or entirely cut off in any other directions. As a result, traffic can only move in small packets of cars; traffic engineers refer to these as "platoons."

Traveling in platoons makes traffic more congested, more dangerous, and less efficient. Cars are forced into driving close to each other at high speeds, increasing the number of chances an accident can take place. Furthermore, it means the roadway is sitting empty most of the time, in between platoons, which is a waste of space and resources.

Roundabouts break up platoons by allowing a constant stream of traffic to flow through an intersection at all times, rather than limiting traffic flow to a series of flash floods in the same direction.

In the late 1990s, the city of Carmel, IN decided to transition many of its intersections to roundabouts. By 2022, the city had over 138 roundabouts, the most of any city in the United States. In that time, Carmel saw a 40% reduction in total accidents and 80% reduction in injury accidents. In 2006, the Carmel Police Department compared the accident rate and cost of each crash at four intersections in Carmel along the same road, two of which had roundabouts, and two of which had stoplights. Due to motor vehicle crashes, the stoplight intersections had an average property damage cost/year of $10,448, whereas the roundabouts had an average damage cost/year of $3,250. Considering roundabouts are exceptionally adept at reducing injury accidents, the difference in medical costs would likely be even greater.

The city also determined that roundabouts cost $250,000 less to build, compared to signaled intersections, and save an additional $5,000/year on electricity costs alone.

Because roundabouts also move traffic more efficiently, Carmel has saved money by not expanding roadways, which can cost $7 million - $10 million per mile, per lane. In addition, the smoother flow of traffic results in less gasoline use, estimated at $7,200,000 per year (based on a gasoline cost of $2.50/gallon). In a city with 37,369 households (2020 US Census), this comes to nearly $200 per household in gasoline costs alone.

When combining the lowered cost of construction for 140 intersections, as well as 20 years of lower electricity cost, fewer accidents, and less gasoline usage, Carmel has saved over $213 million simply by building roundabouts. This doesn’t even include reduced medical costs, nor account for less financially quantifiable benefits, such as noise reduction, improved air quality, improved accessibility for non-motor transportation, and shortened commute time.

Pros:

• Less traffic congestion
• Quieter roads
• Saves on gasoline
• Lower cost to build
• Lower maintenance cost
• Fewer lanes needed
• Fewer accidents
• Safer for bikes and pedestrians

Cons:

• "I just don't like them"