---
title: "Signal-to-roundabout conversion"
url: "https://commonwaysystem.org/retrofits/intersection/signal-to-roundabout-conversion/"
id: "RFT-INT-01"
description: "Replaces an existing signalized intersection with a roundabout, removing signal equipment and phasing entirely in favor of continuous yield-controlled circulation."
updated: "2026-10-18"
---

RFT-INT-01

# Signal-to-roundabout conversion

Replaces an existing signalized intersection with a roundabout, removing signal equipment and phasing entirely in favor of continuous yield-controlled circulation.

## Strategy viewer

Illustration in progress

No illustration of Signal-to-roundabout conversion has been made yet. Interactive views are planned for every pattern and Retrofit Strategy.

## Overview

A signal manages conflict by separating movements in time; a roundabout manages it by separating movements in space, requiring every entering vehicle to yield to circulating traffic rather than wait for a green phase. This retrofit is the most direct route between Signal and the Commonway System's own default intersection control, and is the concrete mechanism behind the System's broader roundabouts-first philosophy.

## Related Media

The items below come from outside the Commonway System, external videos, podcasts, and articles related to this page's topic, not part of the guidebook itself.

Aligned

### [What's Behind Connecticut's Growing Roundabout Push?](https://www.roadsbridges.com/traffic-safety/news/55406667/whats-behind-connecticuts-growing-roundabout-push)

Roads & Bridges

The article reports on Connecticut DOT's roundabout program, including a five-intersection study showing severe crashes down 81 percent after conversion. It is real-world evidence for the Commonway System's roundabouts-first intersection philosophy.

MED-049

## Where this leads: Target patterns

-   [Roundabout (Single/Multi-Lane)](https://commonwaysystem.org/patterns/intersections/roundabout.md) (INT-RAB-01)
-   [Turbo-Roundabout](https://commonwaysystem.org/patterns/intersections/turbo-roundabout.md) (INT-TRB-02) at the highest-volume Arterial-to-Arterial locations

## Applicability and thresholds

Applicable at nearly any signalized intersection where right-of-way exists or can be acquired for the roundabout's circular footprint. Volume alone rarely disqualifies a location, since multi-lane and turbo-roundabout designs scale to high-volume conditions, but right-of-way constraints and adjacent property impacts are the most common practical limits.[3]

## Evidence and effectiveness

FHWA reports roundabouts reduce overall crashes by 35 percent, injury crashes by 76 percent, and fatal crashes by 90 to 100 percent compared to the signals or stop signs they replace.[1] An Insurance Institute for Highway Safety empirical Bayes study of U.S. roundabout conversions found a crash modification factor of 0.801, an approximately 20 percent reduction in crashes overall.[2]

## Getting it built

Cannot be meaningfully piloted or demonstrated. A roundabout requires real construction, new pavement, curbs, and central island, to exist at all; there's no reversible, low-cost version of this conversion. This strategy effectively starts at Permanent on the construction spectrum. See [Construction Methodology & The Build Spectrum](https://commonwaysystem.org/guide/construction-methodology-spectrum.md).

An Intersection Control Evaluation is standard practice before this conversion, comparing the roundabout against retaining or upgrading the signal using the same safety and operational data. See [Decision & Evaluation Processes](https://commonwaysystem.org/guide/decision-evaluation-processes.md).

## Who can move this

Typically a city, county, or state DOT capital project, given the construction scope and cost. Right-of-way needs may bring in acquisition or easement tools. See [Legal & Planning Mechanisms](https://commonwaysystem.org/guide/legal-planning-mechanisms.md) and [Funding & Financing Mechanisms](https://commonwaysystem.org/guide/funding-financing-mechanisms.md).

## Related retrofit strategies

None currently cataloged.

## References

1.  Evidence-based [Federal Highway Administration, "Roundabouts," Intersection Safety.](https://highways.dot.gov/safety/proven-safety-countermeasures/roundabouts)
2.  Evidence-based [Persaud, B. et al., "Safety Effect of Roundabout Conversions in the United States: Empirical Bayes Observational Before-After Study," Insurance Institute for Highway Safety, 2001.](https://journals.sagepub.com/doi/abs/10.3141/1751-01)
3.  Legal / regulatory [Rodegerdts, L. et al., _Roundabouts: An Informational Guide_, 2nd ed., NCHRP Report 672, Transportation Research Board, 2010.](https://nap.nationalacademies.org/catalog/22914/roundabouts-an-informational-guide-second-edition)