The World’s Smallest Roundabout

Article from our Principal Engineer, Kenn Beer

Roundabout, mini-roundabout, compact roundabout, traffic circle, rotunda, rotary… what’s the difference and why?

I was in Mackay, Queensland, this week running a Safe System Assessment course, and saw on Google Maps the ‘𝗪𝗼𝗿𝗹𝗱’𝘀 𝗦𝗺𝗮𝗹𝗹𝗲𝘀𝘁 𝗥𝗼𝘂𝗻𝗱𝗮𝗯𝗼𝘂𝘁’. Of course, this sparked my interest, so I jumped on an eScooter and made my way there with excitement.

While it was impressively small, I’m pretty sure it’s not the world’s smallest. I made a little video explaining a bit about roundabout design. But a few other questions people often ask:
1. What are the different names for circles at intersections?
2. Why would you design something small like this – why not just make it normal size?
Let me give some quick answers, and then I’ll welcome people adding to this in the comments.

𝗡𝗮𝗺𝗶𝗻𝗴 𝘁𝗵𝗲 𝗰𝗶𝗿𝗰𝗹𝗲𝘀 𝗮𝘁 𝗶𝗻𝘁𝗲𝗿𝘀𝗲𝗰𝘁𝗶𝗼𝗻𝘀:
This one is a bit jurisdictionally specific, but in Australia and New Zealand we would call anything with a diameter less than 4m a ‘mini-roundabout’. Anything that is in accordance with Austroads Guide to Road Design Part 4B would be a ‘roundabout’, and anything in between these sizes would be referred to as a ‘compact roundabout’.
The USA likes to use the term ‘traffic circle’ or ‘rotary’ for larger circles in the roadway with more of a traffic flow focus, and roundabouts for smaller circular infrastructure in the intersection with a safety focus. But it’s a bit different state-by-state. Here’s a fact sheet from Washington for those interested: Traffic Circle vs. Roundabout article.

The only place in the world I’ve heard them using the term ‘rotunda’ for a large roundabout is in the Philippines.

𝗪𝗵𝘆 𝗱𝗲𝘀𝗶𝗴𝗻 𝗮 𝗺𝗶𝗻𝗶-𝗿𝗼𝘂𝗻𝗱𝗮𝗯𝗼𝘂𝘁?
As explained in the video, it’s about disrupting ultimate priority and keeping a smooth traffic flow. They work well in lower speed environments.

Some good 𝗾𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 𝘁𝗼 𝗮𝘀𝗸 𝘆𝗼𝘂𝗿𝘀𝗲𝗹𝗳 with mini-roundabouts:
❓ What’s your design vehicle?
❓ Are there appropriate facilities for pedestrians and cyclists?
❓ Is your pavement up to the task?
❓ What are the general operating speeds in the area, and do further speed calming measures need to be added?