Roundabouts: Part 1 Quiz

Hint

The modern roundabout was developed in the United Kingdom to rectify problems associated with these traffic circles. In 1966, the United Kingdom adopted a mandatory “give-way” rule at all circular intersections, which required entering traffic to give way, or yield, to circulating traffic. This rule prevented circular intersections from locking up, by not allowing vehicles to enter the intersection until there were sufficient gaps in circulating traffic. In addition, smaller circular intersections were proposed that required adequate horizontal curvature of vehicle paths to achieve slower entry and circulating speeds.

Hint

For the purposes of this guide, roundabouts have been categorized according to size and environment to facilitate discussion of specific performance or design issues. There are six basic categories based on environment, number of lanes, and size:

• Mini-roundabouts
• Urban compact roundabouts
• Urban single-lane roundabouts
• Urban double-lane roundabouts
• Rural single-lane roundabouts
• Rural double-lane roundabouts

Hint

At some traffic circles, left-turning movements are allowed to occur to the left of (clockwise around) the central island, potentially conflicting with other circulating traffic.

Hint

With a roundabout, it is unnecessary for traffic to come to a complete stop when no conflicts present themselves, or else deceleration will avoid a conflict. When there are queues on one or more approaches, traffic within the queues usually continues to move, and this is typically more tolerable to drivers than a stopped or standing queue.

Hint

The UVC specifies that “when two vehicles approach or enter an intersection from different highways at approximately the same time, the driver of the vehicle on the left shall yield the right-of-way to the vehicle on the right” (UVC §11-401). This runs contrary to the default operation of a roundabout, which assigns the right-of-way to the vehicle on the left and any vehicle in front. This requires the use of yield signs and yield lines at all approaches to a roundabout to clearly define right-of-way.

Hint

Hint

This guide recommends that a roundabout be specifically defined as a single intersection, regardless of the size of the roundabout. This intersection should be defined as the area bounded by the limits of the pedestrian crossing areas around the perimeter of a single central island. Closely spaced roundabouts with multiple central islands should be defined as separate intersections, as each roundabout is typically designed to operate independently.

Hint

Rural roundabouts that may one day become part of an urbanized area should be designed for slower speeds, with design details that fully accommodate pedestrians and bicyclists. However, in the interim they should be designed with approach and entry features to achieve safe speed reduction.

Hint

Hint

Roundabouts are generally safer than other forms of intersection in terms of aggregate crash statistics for low and medium traffic capacity conditions

Hint

Pedestrians are accommodated by crossings around the perimeter of the roundabout. By providing space to pause on the splitter island, pedestrians can consider one direction of conflicting traffic at a time, which simplifies the task of crossing the street. The roundabout should be designed to discourage pedestrians from crossing to the central island, e.g., with landscape buffers on the corners. Pedestrian crossings are set back from the yield line by one or more vehicle lengths to:

• Shorten the crossing distance compared to locations adjacent to the inscribed circle;
• Separate vehicle-vehicle and vehicle-pedestrian conflict points; and
• Allow the second entering driver to devote full attention to crossing pedestrians while waiting for the driver ahead to enter the circulatory roadway.

Hint

Operating and maintenance costs of roundabouts are somewhat higher than for other unsignalized intersections, but less than those for signalized intersections. In addition, traffic signals consume electricity and require periodic service (e.g., bulb replacement, detector replacement, and periodic signal retiming). Operating costs for a roundabout are generally limited to the cost of illumination (similar to signalized alternatives, but typically more than is required for other unsignalized intersections).

Hint

Mini-roundabouts are small roundabouts used in low-speed urban environments, with average operating speeds of 60km/h (35mph) or less. They can be useful in low-speed urban environments in cases where conventional roundabout design is precluded by right-of-way constraints.

Hint

• If a driver intends to exit the roundabout more than halfway around it, the left lane must be used.

Hint

Hint

Elderly pedestrians, children, and the disabled find it more difficult to cross unprotected road crossings. 

Hint

For the purposes of this guide, roundabouts have been categorized according to size and environment to facilitate discussion of specific performance or design issues. There are six basic categories based on environment, number of lanes, and size:

• Mini-roundabouts
• Urban compact roundabouts
• Urban single-lane roundabouts
• Urban double-lane roundabouts
• Rural single-lane roundabouts
• Rural double-lane roundabouts

Hint

The complexity of vehicle interactions within a roundabout leaves a cyclist vulnerable, and for this reason, bike lanes within the circulatory roadway should never be used.

Hint

Roundabouts should always be designed for the largest vehicle that can be reasonably anticipated (the “design vehicle”). For single-lane roundabouts, this may require the use of a mountable apron around the perimeter of the central island to provide the additional width needed for tracking the trailer wheels.

Hint

A splitter island is a raised or painted area on an approach used to separate entering from exiting traffic, deflect and slow traffic, and provide storage space for pedestrians crossing the road in two stages.