1. Module 6 A 21st Century Transportation Network
Roundabouts in the United States
Module 6 A 21st Century Transportation Network
The Role of the Roundabout in Tomorrow’s Transportation System
Welcome to Roundabouts in the United States. Module 6: A Modern Roundabout in the 21st Century
The vision of a single, multimodal transportation network requires the integration of all of the various modes of transportation. This module considers how a roundabout fits in this system and identifies some of the potential benefits.

2. Opportunities that Roundabouts Provide
Lee Rodegerdts
Source Unknown
A well-designed roundabout requires motorists to slow when negotiating the roadway. Because of this, roundabouts can serve as a method to alert roadway users that they are transitioning from one roadway environment to another, such as from the freeway to the local street system, or from a rural environment to one that is more urban.
Source Unknown

3. Opportunities that Roundabouts Provide
Commercial with angle parking
Or it may identify an expected change in traffic behavior between a commercial area and a residential neighborhood.
Residential
Photo: City of Clearwater, FL

4. Opportunities that Roundabouts Provide
PHOTOGRAPHY SOURCE: Lee Rodegerdts
A roundabout can also serve as a gateway to a community by slowing motorists and alerting them that a different roadway environment lies ahead.

5. Opportunities that Roundabouts Provide
Photo: Paul Ryus
Photo: Lee Rodegerdts
A Roundabout can serve as a traffic-calming device in the community, as the roundabout requires motorists to travel at speeds in the range of 20 – 25 miles per hour. This is an effective design that moderates travel speeds at all times. This can proactively support a goal to slow vehicles traveling through the community, which also benefits pedestrians and cyclists.

6. Opportunities that Roundabouts Provide
PHOTOGRAPHY SOURCE: Lee Rodegerdts
Roundabouts also provide a safe and easy method for U-turn maneuvers. This can be a very positive addition to downtown areas and roadways that have a median barrier to separate traffic flows.

7. Initial Construction Cost of a Signalized Intersection
Exhibit 3-16, p. 71
The initial cost to convert a traditional intersection to a roundabout can be more expensive than to simply add a traffic signal, especially if additional right-of-way is required. There is also added initial expense for the design and construction of the roundabout and landscaping the central island. However, many traffic signal installations at traditional intersections require additional improvements, such as the addition of turn lanes, which results in similar design and construction costs.
In locations where a new intersection is being considered, the cost to develop a roundabout is similar to the cost for building a traditional, signalized intersection.

8. Immediate and Long-term Cost Savings of a Roundabout
PHOTOGRAPHY SOURCE: Lee Rodegerdts
There are some immediate and many long-term cost savings associated with roundabouts as compared to signalized intersections that can be realized over time. One immediate cost saving is that a roundabout may not require storage lanes to accommodate the turning vehicles that are common to a signalized intersection. In order to make a signalized intersection operate well, turn lanes and storage lanes are often required for motorists who are stopped at a red light. Since motorists are not required to stop as they approach a roundabout, there is no need to store vehicles on the roadway in advance of the intersection. This can translate into reduced right of way requirements and construction costs.

9. Long Term Costs of a Roundabout Compared to a Signalized Intersection
Lee Rodegerdts
Lee Rodegerdts
As roundabouts do not incorporate traffic signals, they do not require a constant power supply. This means that a roundabout can continue to function during power failures. Also, roundabouts do not require the installation or maintenance of the traffic detection devices associated with traffic signals.
The cost to install and maintain landscaping can be higher with a roundabout than a signalized intersection, but this is dependent upon the amount of landscaping in the center island and in the general vicinity.

10. Air Quality
A 4-way stop intersection or signalized intersection can result in significant traffic queues and delays for motorists. In addition, the greatest amounts of harmful emissions from motor vehicles are created as motorists accelerate and decelerate. This can often occur when traffic volumes reach capacity, when traffic signals are poorly spaced, or signals aren’t timed to maximize traffic flow.
KAI has recently completed a project that evaluated the likely emissions when comparing a signalized intersection to a roundabout, KAI is in the process of requesting permission to use the findings in this presentation.

11. Air Quality
A roundabout can help to reduce the impact of harmful emissions from vehicles since motorists will tend to idle less at a roundabout.

12. Safety Benefits Associated with Roundabouts
PHOTOGRAPHY SOURCE: Fred Ranck
The most important long-term benefit is the significant reduction in the number and severity of crashes that are likely to occur with a roundabout as compared to other intersection designs. This translates into reduced costs of emergency response, reduced travel delays for other road users when a crash occurs, and reduced costs to property damage. Obviously, the most important savings is the reduction in the number of crashes where people are injured or killed in an auto-related crash.

13. A Modern Roundabout Photo: Maryland SHA Photo: Lee Rodegerdts
The modern roundabout can be used in a variety of urban and rural settings and with a variety of configurations ranging from mini-roundabouts to large multilane roundabouts and interchange ramp terminals. Motorists and transportation professionals alike are realizing the broad potential application and benefit to considering roundabouts along with traditional intersection designs.