Town engineer: How to navigate the mini-roundabout on Rosedale Road at General Johnson Road

A guest post by Jim Purcell, Princeton Assistant Municipal Engineer

The new roundabout on Rosedale Road at General Johnson Road has been in operation for two months now. As with all new things, there has been some confusion among motorists and bicyclists on how to navigate this traffic-calming device.

 The roundabout at this intersection is a “mini-roundabout.” A mini-roundabout is intended to allow the majority of traffic to maneuver around the central island at a slow speed. It is constructed in areas where a conventional roundabout cannot be built due to constraints such as physical obstructions or available land. In the case of the Rosedale Road roundabout, physical constraints include utilities, the nearby sewer pump station, environmentally sensitive areas, and steep slopes near Stony Brook. A conventional roundabout here would have required taking land from both the Greenway Meadows Park and the open space on the north side of the road.

A mini-roundabout is specifically designed with mountable interior curbs to allow for larger vehicles – fire trucks, school buses, and delivery trucks – to be able to maneuver the central island. This is intentional, but it can be easily misunderstood. In many cases, mini-roundabouts do not have any landscaping or other features in the center for that reason – they could constitute obstructions and hinder the ability of these larger vehicles to maneuver the mini-roundabout.

There are many reasons why roundabouts are being used at intersections such as this one. Safety is the primary reason – roundabouts reduce crashes and slow traffic to speeds that result in less severe crashes if they were to happen. Modern roundabouts reduce severe crashes at intersections by an average of 80%. Efficiency is another reason – a more efficient intersection is a safer intersection1. In the case of the Rosedale Road – General Johnson Road intersection, motorists leaving Johnson Park School during morning and afternoon peak hours were experiencing significant delays and difficulty in turning onto Rosedale Road. These delays and difficulties often result in risky behavior that can lead to crashes.

Pedestrians crossing Rosedale Road found this intersection to be difficult as well. With the new roundabout and additional rectangular rapid flashing beacon (the pedestrian warning signs) and refuge islands on either side of the roundabout, pedestrians crossing the road are significantly safer.

So, do you know the rules of the roundabout? They are fairly simple – Slow, Look, Yield:

    • Going slow provides more time to make decisions and to be better prepared to yield to other road users.
    • Entering the roundabout at a slower speed ensures that crashes that do happen are much less severe.
    • Slowing down helps drivers do a better job of seeing pedestrians and bicyclists and sharing the road with them.
    • Look around to see other drivers, bicyclists, and pedestrians to anticipate their movements.
    • Obey the signs and markings. There are speed reduction signs, yield signs, and pavement markings to help in maneuvering the roundabout.
    • Keep looking around and checking the crosswalks to see if anyone is waiting to cross or is already crossing. Be ready to stop and let them safely finish.
    • Drivers must yield to traffic in the roundabout. Drivers and bicyclists in the roundabout have the right-of-way.
    • Bicycles can use the full lane – do not pass them in the roundabout.
    • Use your turn signals if it isn’t clear to others where you are heading.
    • Look around one more time for anyone in the crosswalk and be ready to yield to them as you exit the roundabout.

A very important concept of roundabouts is that vehicles entering the roundabout are required to yield to vehicles in the roundabout. Vehicles in the roundabout should not stop while traveling around or through.

If everyone follows these simple rules, all of the users of Rosedale Road can safely travel, whether on foot, by bike, or by car.


  1. With nothing in the center or more than an inch or two above the road bed, it is very hard for the driver approaching the roundabout to know there is something diverting his straight line thru the intersection. Do trucks really need to go thru the center of the raised portion? Even a pulsing light at the center of the circle which could be inserted so that it doesn’t protrude above the level of the low concrete barrier would be helpful.

  2. Unlike most states, NJ has no regulation governing which vehicle should yield to which when entering a traffic circle. (If you believe this is too ridiculous to be true, go and try to find the regulation.) If Princeton wants drivers to yield, they should put up signs to clarify.

    1. They have yield signs and dotted white lines indicating that traffic in the roundabout has right of way.

  3. There are Yield signs and white dotted lines indicating that the traffic in the roundabout has the right-of-way.

    1. Thanks Phil, glad to hear that there are yield signs! So, the reason that drivers should yield to traffic in the roundabout is because there are yield signs (and not because it’s a roundabout, as the guest post claims).

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