4-Way Stop vs. Roundabout – MythBusters Experiment

MythBusters set up an experiment to determine which intersection works better – 4 Way Stop Signs or Roundabouts – check out the ten minute video below.

Experiment Setup

  • In a parking lot with barrels
  • Single lane approaches at four legged intersection
  • Show driver which way to go (left, through, right) as they pull up to the intersection
  • Test for two 15 minute periods and present average
  • Test all way stop, uncontrolled with “traffic cop”, and roundabout (let drivers warm up in roundabout for a half an hour since we’re Americans, arguably not used to roundabouts)
  • Looked like about forty cars were circulating, enough to keep queues on all four legs
  • Count the total number of cars that goes through the intersection during 15 minute period

Results

Roundabouts win with 460 vehicles going through the intersection during the 15 minutes.  All way stop signs had 385 vehicles go through in the 15 minutes and the traffic cop had 289 vehicles go through.  Roundabouts also have a safety advantage with less severe crashes.

Of course stop signs are a lot cheaper than a roundabout, so there are plenty of intersections that don’t warrant the extra cost of a roundabout but are just busy enough to need all way stop signs.

Takeaway question – should we ever use traffic cops or just go to all way stop control?

 

Need to calculate roundabout capacity? Check out our roundabout capacity analysis spreadsheet. An easy-to-use spreadsheet that can easily be adjusted for standard defaults, such as lane utilization, critical headway or follow-up headway, according to local factors.

 

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One thought on “4-Way Stop vs. Roundabout – MythBusters Experiment

  1. It’s worth noting that they constructed a Concentric Single-Lane roundabout, the type that has separation between entry and exit points rather than a unified conflict point. The drivers, taking the fastest path in the absence of a truck apron, drove in a pattern that began to resemble a crossing roundabout.

    The difference in gap selection of crossing versus joining means that, had they designed a MUTCD-compliant roundabout (without separation between entry and exit conflict points), the intersection probably would have performed even better. Under the MUTCD design, drivers also wouldn’t be decelerating in order to exit the intersection, which causes greater “friction” within the intersection due to braking, which also would have increased the throughput.