Speaking

Building “Compact Roundabouts” has shown to be an expeditious and affordable way to solve mobility and safety problems at existing traditional intersections, be it stop-controlled, signalized or an uncontrolled intersection location. The term “urban compact” roundabout was first introduced to the US transportation profession in the first Federal Highway Administration (FHWA) Guide published in 2000. However, subsequent guides did not carry forth this term, and in hindsight, the term had value and merit further development. 

This presentation will acknowledge and share the value gained by implementing smaller roundabouts and those specifically defined as “compact roundabouts” in the project designation at the road owner’s agency or in components of the smaller diameter roundabout. Additionally, this presentation will share examples of compact roundabouts on the system, including local arterials and state DOT roadways and ranging from 80- to 110-foot inscribed diameters and details of locations of operating compact roundabouts.

A compact roundabout functions similarly to a mini roundabout. For decades in the United Kingdom, mini roundabouts were usually the intersection control of choice due to the lower cost of using paint to define the central portion of the roundabout and mirror the same overall footprint of the existing intersection. Examples will highlight compact roundabout construction to show less expensive than normal-sized roundabouts. A mini-roundabouts function allows larger vehicle movements, usually termed the design vehicle, and passenger vehicles were critical at that existing intersection. Through examples and a case study, a U.S. compact roundabout will be shown to replicate the operations and safety of a normal-sized U.S. roundabout.

Speakers will also present in detail the design elements, including key geometric and roadway elements necessary for the successful implementation of a compact. Select areas of the U.S. brought compact roundabouts into broader use and defined them either in state design guidelines or programmatic designations. Ohio and Washington State have successfully implemented numerous compact roundabouts across a wide array of contexts and road classifications, proving smaller compact roundabouts should be more universally applied where larger roundabouts are dismissed due to their expansive footprint requirements. Roundabouts, in general, are chosen to solve safety and mobility problems. However, smaller roundabouts create discussions involving compromises or tradeoffs, including the decision to move ahead or eliminate a roundabout for consideration. Compact roundabouts are proven effective in solving mobility and safety for all users.

When compact roundabout design alternatives meet location-specific site constraints, the tradeoff discussion allows more subjective conversation on context, vehicle mix and active transportation needs to address safety and delay reduction for all users. Case study locations will share how the original roundabout design was too large and the decision moving forward precluded the roundabout. However, when other alternatives did not mitigate either the mobility or safety problem and do nothing was the outcome, a compact roundabout was reintroduced, and a compact roundabout alternative would prove to be a better path forward than the “do nothing” outcome. Additionally, with compact example projects, it will be shown how assumptions and tradeoffs of the selection will need to be clearly communicated to road owners and users of the facility in the public engagement process to align with expectations. The presentation will demonstrate in most examples of compacts, road owner's ability and willingness to tackle previously difficult intersection locations without requiring extensive environmental mitigation, purchasing property, or having to treat new impervious drainage in expensive detention facilities.