2.3 Roundabouts and Rotary Traffic Flow

Modern roundabouts are increasingly built throughout Mississippi—including interchanges in Olive Branch, Oxford, Hattiesburg, and Biloxi—to improve traffic flow and safety. According to the Federal Highway Administration (FHWA) and the Mississippi Department of Transportation (MDOT), modern roundabouts reduce fatal and injury crashes by nearly 80 percent compared to signalized intersections. Mastering roundabout navigation, entry yielding, and lane discipline is vital for the Mississippi driver license test.

Understanding the Modern Roundabout

A modern roundabout is a circular intersection where traffic moves counter-clockwise around a central island. Roundabouts are engineered around two strict principles: yield-at-entry control and low circulating speeds (15 to 25 mph).

Roundabouts achieve safety through geometry. A standard four-way intersection features 32 vehicle conflict points, including 16 crossing points that cause deadly perpendicular 'T-bone' and head-on crashes. A single-lane roundabout reduces conflict points to just 8, all of which are low-speed, same-direction merging movements. Broadside impacts are practically eliminated.

Core Principles of Rotary Flow: Counter-Clockwise Circulation and Yielding

All Mississippi roundabouts operate under two non-negotiable rules:

1. Traffic Always Circulates Counter-Clockwise: All entering vehicles turn right into the circle and travel counter-clockwise around the central island. Driving clockwise or attempting a direct left turn into the circle is an extremely dangerous, test-failing violation.
2. Yield at Entry: Under Mississippi law, entering vehicles must yield to circulating traffic already traveling inside the circle. Circulating vehicles approaching from your left have absolute priority. Drivers must slow down or stop at the dashed yield line and wait for a safe gap before entering.

Entering drivers must also yield to pedestrians and cyclists crossing in crosswalks across entry lanes.

Lane Selection Before Entering Multi-Lane Roundabouts

In a multi-lane roundabout, you must select your lane before entering, following overhead signs and pavement arrows:

Right-Lane Assignment

The right lane is designated for drivers intending to:

• Turn Right (First Exit / 90 degrees): Stay right, signal right, and depart at the first exit.
• Travel Straight (Second Exit / 180 degrees): Enter in the right lane, circulate on the outer ring, and exit straight across.

Left-Lane Assignment

The left (inside) lane is designated for drivers intending to:

• Travel Straight (Second Exit / 180 degrees): Where two through lanes exist, through traffic may use the left lane.
• Turn Left (Third Exit / 270 degrees): Enter from the left lane, circulate on the inner ring past the first two exits, and exit at the third road.
• Make a U-Turn (Fourth Exit / 360 degrees): Enter left, circle the island, and exit back in your original direction.

Rules of Movement Inside the Circulatory Roadway

Once inside a roundabout, drivers must observe two strict rules:

Never Stop Inside a Roundabout

Do not stop inside the circulatory roadway unless avoiding an imminent collision. Stopping blocks traffic and causes rear-end crashes. If you miss your exit, never stop or reverse. Circulate around the island again and exit smoothly on your next pass.

Never Change Lanes Inside a Roundabout

Changing lanes inside a roundabout causes blind-spot side-swipes. Remain in your entry lane until completing your exit.

Large Commercial Vehicles and Truck Aprons

Modern roundabouts feature a raised paved ring around the center island called a truck apron. Large semi-trucks, logging trucks, and buses have long wheelbases that cannot negotiate tight curves without their rear trailer wheels 'off-tracking' onto this apron. The truck apron safely accommodates off-tracking without overturning.

When near commercial trucks:

• Never drive alongside a truck in a multi-lane roundabout. Trucks often require both lanes to complete turns.
• Stay back at the yield line until the truck clears the roundabout, then proceed behind it.

Emergency Vehicles in Roundabouts

When an emergency vehicle with flashing lights or sirens approaches:

• If Approaching the Roundabout: Pull right before reaching the yield line, stop, and let the emergency vehicle enter.
• If Already Inside: DO NOT STOP inside the circle. Stopping blocks the curved lane and traps emergency vehicles. Continue at normal speed to your exit, clear the circle, and then immediately pull over to the right shoulder and stop.

Exiting a Roundabout: Signalling and Pedestrians

When departing a roundabout:

1. Signal Your Exit: Turn on your right turn signal after passing the exit preceding your intended exit to notify waiting drivers.
2. Yield at Exit Crosswalks: Pedestrian crosswalks cross exit lanes. Yield to crossing pedestrians before accelerating onto the departing road.

Roundabout Protocol Matrix

Common Roundabout Exam Traps

• Trap 1: Believing entering traffic has priority. Circulating vehicles inside the roundabout always have right-of-way.
• Trap 2: Stopping to let someone enter. Stopping out of courtesy violates traffic law and causes rear-end collisions.
• Trap 3: Turning left into the circle. You must always turn right and circulate counter-clockwise, even when making a left turn.