Roundabouts have been proven to be safer and more efficient alternatives to traffic signals and 4-way stop sign controlled intersections.  One reason for these improvements is that roundabouts depend on the training and judgement of the driver more than other intersection controls and no computer can outperform the capability of thousands of well-trained drivers.  Another is that due to the demands of the traffic environment drivers tend to be more conscious and defensive while navigating roundabouts.

By observing the following tips you will help to improve driving conditions for your fellow drivers and reduce the risk of a collision:

	•         Approach the roundabout as you would a typical four-way intersection: o    If you are making a right turn, you should be in the right lane; o    if you are making a left turn, you should be in the left lane; o    through movements can be made from either lane.
	•         YIELD to traffic already in the roundabout and pedestrians in the crosswalks.
	•         DO NOT turn left at the splitter island. •         Once you are in the roundabout; o    travel in a counterclockwise direction; o    check for exiting traffic, and; o    DO NOT CHANGE LANES.
	•         If you entered the roundabout in the right lane; o    look for your street; o    use your right-turn signal, and; o    exit the roundabout.
	•         If you entered the roundabout in the left lane; o    look for your street; o    check your blind spots for traffic; o    use your right-turn signal, and; o    cross over the outside lane to exit the roundabout.
	•         As you exit the roundabout, watch for and yield to pedestrians and bicyclists.
	•         If you miss your street, travel around the roundabout again and exit at the desired street; o    check for exiting traffic.

There Florida Department of Transportation created A Guide to Roundabouts, a pamphlet which provides more detailed information about driving roundabouts.  Also, the state of Wisconsin Department of Transportation created an animation which provides excellent guidance.  By observing the preceding roundabout rules you will improve conditions and reduce the risk of causing a collision.

The Federal Highway Administration (FHWA) published the Roundabouts: an Informational Guide report in the year 2000.  Within the guide the FHWA published the results of several studies in Australia, France, Germany, the Netherlands, the United Kingdom, and the United States where signalized intersections were replaced by roundabouts.  In summary the studies found the following:

•         The average reduction in total reported crashes ranged between 36 percent and 61 percent.

•         The average reduction in injury crashes ranged ranged between 25 percent and 87 percent.

The Insurance Institute for Highway Safety has a number of articles discussing the safety benefits of roundabouts.  According to their informational page on roundabouts several independent studies of 23 converted intersections show 40 percent reductions in total crashes and 80 percent reductions in injury crashes.  They have also been shown to reduce collisions involing pedestrians and bicyclists.

This reduction in crashes occurs for several reasons:

There are less conflict points between vehicles in roundabouts than at signalized intersections.  As the locations for potential crashes decreases, so does crash frequency.  For example:  

Traffic signals allow vehicles to proceed at the speed limit, generally in the 35 to 50 mph range.  At those speeds the reaction time necessary to avoid a collision is very small, and the distances required to stop are very long.  For example, a vehicle travelling at 25 mph needs approximately 155 feet to stop whereas a vehicle travelling at 50 mph requires approximately 425 feet.  A difference in speed of 25 mph requires an additional 270 feet.   Any danger requires early detection and response.

Roundabouts are designed to keep speeds in the range of 25 mph.  Lower speeds mean that drivers have more time to react, increasing the probability of avoiding a collision.  Lower speeds also mean vehicles have less momentum which substantially reduces stopping distance and reduces the amount of energy vehicles impart when crashes happen.  That is why crashes in roundabouts tend to be “fender-benders”.

On February 2, 2010 the Engineering Division conducted a speed study in the Wickham/Lake Andrew roundabout to determine the 85^th percentile speeds in the approaches, circulatory roadway, and exits to the roundabout (the 85^th percentile speed is defined as the speed which 85 percent of the vehicles are travelling at or under, when measured under free-flowing conditions).  The results of the study are included below, and show that most vehicles in the circulatory road travel between 10 to 24 mph.

The damage caused When two vehicles collide is directly related to how fast the vehicles were travelling relative to each other.  For example; in a race track, two vehicles travelling behind each other at 100 mph and 102 mph collide travelling in the same direction.  The collision does minor damage because the relative speed is 2 mph.  Such collisions occur relatively frequently and do not always cause problems for the drivers.  However, if one of the vehicles was travelling at 2 mph and was rear-ended by a vehicle travelling at 100 mph, the relative speed is 98 mph, and the collision would cause severe injuries.

In a traffic signal there are vehicles travelling at 35 to 50 mph past vehicles that are stopped, travelling perpendicular to their path, or worse.  The FHWA estimates in their report on Intersection Safety that rear end and and sideswipe collisions make up 9 percent of all collisions at intersections.  In those cases relative vehicle speeds are high (35-50 mph if one vehicle is stopped), causing greater damage during collisions.

In a roundabout all vehicles are travelling in a counter-clockwise direction in the circulatory roadway and are maintaining low relative vehicle speeds.  In the case of a collision, the relative speed means that vehicles will impart less damage.  The speed study conducted by Brevard County shows that relative vehicle speeds in the circulatory roadway range between 5 and 10 mph.

The direction of two vehicles in a collision will make significant difference in the damage caused.  To revisit the previous example; we know that two vehicles travelling in the same direction at relatively the same speed will cause minor damage.  However, if one of the vehicles was turned around and travelling at 100 mph, while the other vehicle approached at 102 mph,  the vehicles would collide head-on at a relative speed of 202 mph and the resulting collision would likely be fatal.

The FHWA estimates in their report on Intersection Safety that left-turn or right-turn collisions make up 45 percent of all collisions at intersections while head-on (opposite direction) crashes make up about 14 percent.  In other words; in 59% of all intersection crashes vehicles are travelling in directions which result in damage caused by a combined speed that is greater than the speed of either of the vehicles alone.

If a collision does occur at a roundabout the angle of impact is small because crashes are between vehicles travelling in, or close to, the same direction.  An extraction of all crashes reported to the County’s database that occurred during 2008 at the Lake Andrew & Wickham roundabout shows that 40% of all crashes were “angle” crashes, indicating an angle less than 90 degrees, and the remaining 60% were sideswipes.  In those conditions, because the angle of impact is small, the resulting damage is also small.

Various sources estimate that signalized intersection maintenance costs between $3,000 and $5,000 per year.  These costs include:

·         Electricity:

o    Traffic signals require electricity 24 hours a day, 365 days a year.

·         Maintenance of equipment:

o    Traffic signals are composed of expensive and sophisticated electrical components.

o    Traffic Signal Maintenance can only be performed by qualified signal maintenance technicians certified by the International Municipal Signal Association.

o    Equipment must be replaced regularly as it is constantly subjected to a harsh environment.

o    Traffic signal maintenance sometimes requires law enforcement support to maintain safe traffic flow at additional cost.

·         Emergency repairs:

o    Traffic signals are susceptible to damage from the effects of heavy rains, lightning, hurricanes, power outtages, power spikes, traffic crashes, vandalism, road construction, corrosion, temperature fluctuations, insects, rodents, sun, and a variety of other factors common to our environment.

o    Traffic signal failures often require the deployment of law enforcement to maintain safe traffic flow.

o    Emergency traffic signal maintenance means qualified staff must be available 24 hours a day, 365 days a year to respond to traffic signal outtages.

The maintenance costs directly associated with a roundabout are limited to landscaping and sign maintenance which is substantially less expensive and usually performed as part of normal right of way maintenance operations.

As population changes in the County so do traffic flows.  New families add vehicle trips to our roadways and therefore demand more time from our traffic signals.  In order to accommodate the changes in traffic volume signals must be re-timed regularly.  It is recommended that signals be re-timed at least once every two years but construction of big developments (i.e. a new shopping center) could require adjacent signals be re-timed sooner to account for the change in traffic volume.  Traffic signal timings must be developed by a qualified traffic engineer, which can cost thousands of dollars, particularly if signals are part of a string of closely spaced signals which must be re-timed together to maintain good flow.

Roundabouts do not require timings because they are constructed to depend on the driver to determine when they have the right of way.

All traffic signals use the familiar green-yellow-red sequence in order to safely manage traffic.  The delay associated with intersections is caused by:

·         Delay to vehicles stopping during the yellow change interval;

·         Delay to all vehicles during the all-red interval;

·         Delay to vehicles as they start to move during the start of their green light; and

·         Delay to vehicles waiting for their green light.

Those delays are built into the system which intersection controllers depend on for safe operation.  Unfortunately, these safety features will tend to delay vehicles unnecessarily.

The Roundabouts: an Informational Guide document shows that roundabouts tend to provide less approach delays.  This is due in large part to the fact that roundabouts are yield-controlled intersections and allow constant traffic flow.  Because multiple vehicles will be able to enter the intersection without stopping from multiple directions, and simultaneously make what would be considered “conflicting movements” at a traffic signal, roundabouts offer substantially less delays to traffic.  Also, each driver is evaluating their approach and making the most optimal decision for their situation, instead of having to wait until they are assigned the right of way.

The capacity of a roundabouts tend to be higher than that of equivalent signalized intersections. Less delays means more vehicles can travel through the intersection in an hour, for example.  Also, because all through and turning movements are allowed at the same time, it provides a further capacity increase.  Furthermore, traffic signals are designed to allow the major movement to have the majority of the green light, meaning that side streets have longer waits.  By not assigning right-of-way to any particular direction roundabouts provide equal opportunity to the major and side streets.

Roundabouts, with their landscaped center islands and splitter islands tend to be much more pleasing to drivers than traffic signals, which are beautiful only to the engineers who design them.

We hope that this document has provided some valuable information on the proper function, operation, and reasoning behind roundabouts.  If you have further questions please feel free to contact the Public Works Engineering Division at (321) 633-2077.