Roundabout (Single / Multi-Lane)
INT-RAB-01 Roundabout (Single / Multi-Lane)
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.
Are Streets Too Complicated Now?
Asks whether today's proliferation of lines, signals, and lane types on streets is overcomplication or a needed response to modern demands, a question that runs directly through CS's Element-scale catalog and the density-tiered Corridor retrofit paths this video is tagged to.
Why Aren't Dangerous Drivers Punished?
Traces why traffic law rarely punishes road violence proportionally, then makes the case CS already builds on: infrastructure should be designed so mistakes aren't fatal, rather than relying on punishment after the fact.
America Built the Wrong Roundabout (The Dutch Didn't)
Traces the turbo roundabout's origin and safety data, but also reports the Fietsersbond's documented cyclist/pedestrian crossing hazards at turbo roundabouts directly, worth noting since it complicates a clean "aligned" label.
Are Roundabouts Actually Better Than Traffic Lights?
A real head-to-head test (Carmel, IN) backing the case for roundabouts on time, fuel efficiency, and crash severity, while being upfront about roundabouts' accessibility gap for blind pedestrians.
Roads don't have to be FAT to be FAST
Explains the interrupted-flow/platooning physics behind signalized-arterial congestion, then covers Carmel's Keystone Parkway conversion to a limited-access road using compact elevated roundabout interchanges instead of a full diamond interchange.
Let's FIX the HIGH SCHOOL (with 152 ROUNDABOUTS!)
The origin story of Carmel's roundabout program, starting with a contentious school-zone traffic-calming project, and the engineering fix (tightened entries, fatter center island) that made the design work.
Typical at: Suburban Compact Urban Core
Rural is an edge case. Undeveloped is an unlikely pairing.
Design notes
Roundabout is the default control wherever two Collector-or-higher streets meet within the Commonway System's intersection philosophy. Traffic signals remain available but only as a documented last resort, and turbo-roundabouts take over at the highest-volume Arterial-to-Arterial junctions.12
Freight-priority streets
When this pattern serves a freight-priority street (Industrial Collector or any Typology carrying significant truck volume), size the inscribed circle diameter to the current NCHRP Research Report 1043 guidance for large vehicles, rather than the base passenger and bus vehicle range.1
The truck apron is for the occasional oversize check vehicle. The everyday design vehicle should clear the roundabout within the traveled way without off-tracking onto the apron.3
Two cautions apply. Designing every movement for the largest conceivable truck degrades safety for vulnerable users without a demonstrated need, so confirm actual vehicle-classification counts first.3 And oversized intersections carry their own costs: more crash exposure, more confusion, more right-of-way, and longer pedestrian crossings.4
Related patterns
Turbo-Roundabout (INT-TRB-02) (the step up for higher-volume Arterial-to-Arterial junctions, per this page), Signal (INT-SIG-03) (the alternative control competing for the same higher-volume intersections, per Signal's own Design notes), Neighborhood Traffic Circle / Mini-Roundabout (ELM-NTC-46) (the much smaller, unsized analogue for a Local-to-Local intersection), Industrial Collector (COL-IND-03) (a freight-priority street whose intersection answer depends on this page's freight-street sizing note)
Getting there: Retrofit path options
Signal-to-roundabout conversion (RFT-INT-01)
References
- Legal / regulatory Transportation Research Board, Guide for Roundabouts, NCHRP Research Report 1043 (2023). Supersedes NCHRP Report 672.
- 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).
- Legal / regulatory Delaware Department of Transportation, Design Guidance Memorandum (DGM) 1-26, "Roundabouts" (design vehicle versus check vehicle, and the caution against over-designing for the largest possible truck).
- Legal / regulatory Wisconsin Department of Transportation, Facilities Development Manual, FDM 11-25 (costs of oversized truck-accommodating intersections).