by Alex Fagnand, Keith Hall, Max Scheideman & Kate Drennan.
- Executive Summary
- CROW Manual on Roundabouts
- Single Lane Roundabouts
- One-way Cycle Tracks
- Two-way Cycle Tracks
- Two-way Cycle Tracks: A Case Study
- Bike Lanes in a Roundabout
- Mixed Traffic
- Multi-Lane Roundabouts
- Crow Manual Design Guidelines for Roundabouts
- Roundabout Inventory – Delft, Rijswijk, Ypenburgh-Leidschendam
In the Netherlands, roundabouts have become a commonly used treatment at intersections. They are favored because of their excellent safety record, as well as the ability to continuously move vehicles, bicycles and pedestrians through an intersection, minimizing delay to all modes. Roundabouts are often paired with separated cycle tracks, though they sometimes contain striped bike lanes or mixed traffic with no bicycle treatment. According to the CROW Manual, which sets road design standards, separated cycle tracks are considered the safest treatment, and striped bicycle lanes are the least safe.
At most roundabouts, cycle tracks rings the vehicle lane. The cycle track is given priority over entering and exiting vehicles, reinforced by ‘sharks teeth’ which instruct users where to yield. Many roundabouts also have other traffic calming and safety features such as red bricked paths(commonly used for bike facilities), raised and striped crosswalks for pedestrians, and sometimes yield signs instructing auto users to be mindful of pedestrians and cyclists. Though two-way cycle tracks were discouraged in the past, more recently thinking has changed and many modern roundabouts now include cycle tracks moving in both directions. Observations and field counts have shown that roundabout users in the Netherlands have very high rates of compliance toward yielding, reinforcing the belief that roundabouts are a very safe and effective method for dealing with intersections.
CROW Manual on Roundabouts
The Dutch Design Manual for Bicycle Traffic (CROW, 2007) guides planning and design of roundabouts in the Netherlands. There are big differences between single-lane and mulit-lane roundabouts. According to the manual, whenever possible the intersection should have a single lane roundabout. These are the safest for pedestrians, bicyclists and vehicles because there are fewer conflict zones and decision points. If more capacity is needed, a two lane roundabout can be built, and is preferred over a signalized intersection in rural areas where there are few pedestrians. However, in urban areas multilane roundabouts are almost never used because of the hazard they pose to pedestrians.
Where multilane roundabouts are needed, the CROW manual calls for a fully separated bypass route or a below grade underpass for cyclists and often pedestrians. The “turbo-roundabout” is the preferred form form multilane roundabouts.
On single lane roundabouts with light traffic, bicycles sometimes share the circulatory lanes with cars. Most of the time, however, Dutch roundabouts have a separate path (cycle track) for bicycles. Dutch policy is that within built-up or urbanized areas, the bike path has priority where it crosses roundabout entries and exits, while in rural areas the bike path must yield priority at roundabout entries and exits.
Click Here for a video showing an example of bike priority at a Dutch roundabout.
The CROW manual also makes recommendations for how to separate a cycle track from the road at a roundabout. A “relatively quiet” roundabout, up to 6000 PCUs per day, requires no dedicated bicycle facilities. However, installing a cycle track is still encouraged to improve subjective safety (the feeling of safety). Many cyclists, especially children, feel uncomfortable sharing a sharply curved lane with motor vehicles. Above 6000 PCUs, dedicated cycle tracks are required. Striped bike lanes are not recommended based on research showing their higher crash rate. Because of this, some Dutch roundabout with bike lanes have been retrofit to create cycle tracks. However, there are still several roundabouts with bike lanes in the Netherlands that have not seen any safety problem, which is why the bike lanes have been retained.
The following graph, which forms the basis of the CROW recommendations, shows the number of casualties per year as a function of the volume of motorized traffic for different kinds of bike facilities at roundabouts. (Source: ”Pedestrian and Bicycle Friendly Roundabouts: A Dilemma of Comfort and Safety,” a presentation by Lambertus G. H. Fortuijn of the Stategic Policy office of the province of South Holland and the faculty of TU Delft.)
Number of Casualties per Bicycle Facility – Lambertus G.H. Fortuijn, Pedestrian and Bicycle Friendly Roundabouts
This graph illustrates that where daily traffic volume at a roundabout exceeds 5000, the treatment with the least casualty rate for bikes is a dedicated, separated cycle track. The next safest design is no bike facility or treatment at all. The most worst safety record is for roundabouts with painted bike lanes. However, it should be noted that bicyclist volume is not accounted for in this analysis. The apparent advantage that “no path” has over bike lanes may be because bike lanes tend to be used where bicyclist volumes are higher, and “no path” where bicyclist volumes are lower.
The reason for bike lanes’ poor safety record is thought be related to right-hook crashes at exits. Bikes stay to the right to avoid slowing cars, but often don’t have the sight line to see a car starting to turn into them. Because of their close proximity they may not have the reaction time to yield or accelerate to avoid a turning car. In roundabouts with no facilities, bikes may be more likely to take the lane and cars will not attempt to pass or hook right in front of a cyclist. However, because roundabout lanes tend to be wide (5.5 m or 18 ft), it can be hard for bikes in a “no path” roundabout to take the lane, exposing them to right hooks as well.
The CROW manual also states that at the location where a cycle track crosses the spurs leading to / from a roundabout, the bike facility needs to be extremely visible and conspicuous. A driver of a motor vehicle should have excellent sight lines while approaching the roundabout exit, and be looking for a bicycle traveling parallel to them on their right. The cycle track facility itself should also be clearly designated with red asphalt, or other visibly different pavement, and proper signage. Furthermore, the entries and exits to and from the roundabout should have the “shark’s teeth” marking applied to the pavement indicating that the motorist must yield to crossing cyclists. There must also be “elephant’s feet” markings indicating the location of the cycle track crossing (because colored pavement is not sufficiently visible at night). In the photo below, in addition to those features, there are “piano key” markings that indicate an elevation change in the form of a very mild speed hump. The raised crossing is so mild that it doesn’t really slow motor traffic, but it works to grab a motorist’s attention that they are about to cross a special zone.
Cyclist Priority at a Roundabout Leg Crossing
The CROW manual does not specify a particular type of curbing or separation method for cycle tracks, but it is clear from Dutch practice that designers believe that greater separation leads to greater safety. This principle applies up to 6 meters of separation, after which point Dutch law considers the cycle track an entirely separate road, with confusing consequences regarding priority. Since there is no separation standard in the manual, the Dutch use many different methods of separation to accomplish the same means of safe passage. A cycle track may be placed 6 meters away with a full raised median dividing motor vehicles and bicycles, or it may run in the roundabout with “hogback” C curbing separating it from the motor vehicle lanes.
Single Lane Roundabouts
One-way Cycle Tracks
When an intersection serves more than 6,000 vehicles a day, a one way cycle track roundabout is the preferred treatment by the CROW manual. They satisfy all of the safety recommendations and requirements previously discussed and create cycle traffic flow in the direction anticipated by motor vehicle operators. This makes the areas where cycle track cross the spurs of the roundabout more safe, but potentially less convenient for the cyclist who may prefer to ride contraflow because it is a shorter distance. One way cycle tracks can be distinguished from two way tracks by the lack of a center line marking and the use of directional arrows to direct bike traffic.
The width of the track is not a clear indication as one-way cycle tracks. In Delft and Rijswijk, one way cycle tracks were between 2 meters (most narrow) and 3.9 meters (widest). Width of the cycle track near a roundabout is typically governed by available space, not function of the track. Still, the average width is approximately 3 meters.
The tracks in Delft and Rijswijk were separated from the vehicles by medians of varying width. These widths ranged from 4 to 5.5 meters and appeared to also depend on availability of right of way rather than a standard. The Dutch also employ simple “hogback C curb” dividers in situations where space is extremely limited; with the resulting cycle track akin to a separated lane. Typically this is done in urban areas such as Rotterdam, where intersections are retrofitted into the available space.
The presence of the hogback curbing not only creates a physical barrier for all motor vehicles, it creates psychological awareness that cyclists will be using the roundabout. Additionally, it prevents motor vehicles from cutting through the cycle track while exiting a roundabout.
Cycle Track separated from the vehicle lane by “Hogback C Curbing”
Click Here for a Hogback “C” Curbing example in Westland, NL.
Two-way Cycle Tracks
At the time of the last publication (2006), the CROW manual recommended against two-way cycle tracks at roundabouts for safety reasons:“Two-way tracks on a roundabout are avoided whenever possible because drivers of motor vehicles do not expect cyclists from the unexpected [clockwise] direction.”
Drivers are less likely to yield to bicycles riding from a direction they are not expecting. This can lead to a collision at roundabout entry points, where a driver looks left for a gap in the car traffic and fails to look right before beginning to move because he or she is not expecting a bike or vehicle from that contraflow direction.
However, in the past few years design policy in the Netherlands has shifted to promote two way cycle tracks. The governing opinion in some municipalities is that two-way tracks are more convenient and therefore will promote wider use of cycling. They also reason that if a roundabout has two-way cycle tracks on the approaches, it should continue around the circle. This creates better connectivity and minimizes travel distances. Also, the extra width can be used for passing or people who may ride two abreast.
Generally, two-way cycle tracks are nearly the same width as older one-way cycle tracks, averaging around 3 meters. The median structures for two way cycle tracks are also similar in style and variance of width. The primary difference with two-way cycle tracks is the presence of a center line marking, either a painted stripe or inlaid white brick. In some roundabouts a bi-directional arrow will also be featured beneath the cycle track designation sign. This bi-directional arrow is also intended to alert the motor vehicle approaching to look both ways before entering the roundabout and yield to bicycle traffic coming from either direction.
Two-way Cycle Tracks: A Case Study
The City of Delft, NL recently rebuilt a major signalized intersection in a highly populated area, transforming it from a safety hazard for cyclists and motor vehicle operators to a modern roundabout. Called the Delftlandplein, it is the junction of Papsouwselaan (north leg), Voorhofdreef (south leg), Martinus Nijhoflaan (west leg), and the minor street Minervaweg (east leg).Before the reconstruction, it was a large signalized intersection with three entry lanes per approach, plus a pair of tram tracks in a median reservation making a 90 degree turn. The junction is pictured below in its 2009 signalized intersection form.
Delflandplein before 2009 as a signalized intersection
Rebuilt Delflandplein featuring a modern roundabout with a two-way cycle track and tram / bus roadways through the middle
As part of a road diet (reducing the northern leg, Papsouwselaan to only one through lane per direction), the City of Delft decided to replace the signalized intersection with a single-lane roundabout. Due to Dutch design principles, a roundabout with crossing bicycles and pedestrians — which are unavoidable here — should have only one circulating lane. All of the approaches were therefore reduced to a single entry lane (there had been 3 entry lanes at each leg) and one exit lane, with a cut-through for both trams (making a 90 degree turn between north and west) and buses (running through on the tram ROW from north to south). The roundabout in its current form is pictured above.
The roundabout handles the daily capacity demands so well, that the new roundabout causes less delay for motorists than the old signalized intersection had, even with the 50% reduction in lane capacity. The design of this roundabout has several key features. There is a dedicated busway and tramway running through the middle of the roundabout which receives priority while traveling through the intersection. The only signals on the roundabout are to alert motorists, cyclists and pedestrians of approaching transit vehicles.
The roundabout also features a two-way cycle track. From the picture, one can see the two-way track does not hug the round motorist roadway, but instead the cycle track is squared so that when it meets the roundabout entries and exits, cyclists approach the road at a 90 degree angle. This promotes safety because it increases visibility and awareness for both the cyclist and the motorist. The 90 degree angle solution is not commonly used, but can be applied in situations where there is enough space to expand the footprint of the cycle facilities.
Sometimes simplicity is the best solution. At mixed traffic locations bicycles, mopeds, cars, and trucks all coexist within the same roadway. In these situations the roundabout is generally small with both low volume and speed. There are no signals and all vehicles/cycles have to yield to traffic already in the roundabout. Mixed traffic roundabouts are safer than roundabouts with bicycle lanes because the cyclists can move directly in front of (or behind) the vehicles while passing through the roundabout to prevent any chance of a right hook collision.
Mixed Traffic Observations
There is a mixed traffic roundabout in the city of Delft at the junction of Westplantsoen, Hof van Delftlaan, and Adriaan Pauwstraat in the residential neighborhood of Hof van Delft. It is the only roundabout in Delft without separated bicycle facilities.
Click Here for the location of the mixed use roundabout in Delft.
We performed a sample field count during AM peak hour traffic on Tuesday, July 9th, 2013 for 20 minutes between 9:00am and 9:20am. Bicycles made up the majority of users (66%), followed by passenger vehicles (27%), mopeds (5%), trucks or heavy-grade vehicles (1%), and bus traffic (1%). In total, 237 users were recorded traversing the mixed use roundabout, which is approximately one user every five seconds. The high traffic volume included a variety of users, including school children, middle-aged, and older adults.
Sample field counts, 09-07-2013
Compliance rates for proper yielding in traffic at the mixed roundabout were high and estimated to be above 90%. In most instances, bicyclist entered the mixed traffic roundabout from the advisory lane and took the full lane once they entered the roundabout. Motorists rarely passed bicycles in the roundabout, unless the bicyclist was traveling at low speeds and staying in the outer circumference of the roundabout. In our 20 minute observation, we didn’t observe any near misses and all users seemed secure and comfortable in sharing the roundabout. Furthermore, we did not observe bicyclists needing to stop intermittently or perform drastic maneuvers while interacting with vehicle traffic in the roundabout.
Bike Lane in a Roundabout
As previously mentioned, the least statistically safe bike treatment for a single lane roundabout is placing bike lanes in a roundabout. Thus the CROW manual recommends against it. As of July 2011, however, bike lanes in roundabouts still exist as legacies where they have a good safety record. At the location shown below in Zwolle, this bike lane in a roundabout has a good safety record, traffic volumes are well above the 6,000 vehicle/day limit for mixing bikes with cars, and the bike lane is heavily used.
Roundabout in Zwolle, NL featuring a bike lane.
One way to retrofit a bike lane in the roundabout is to create a one-way cycle track with no median, by placing “Hogback C Curbing” in the roundabout between the motor vehicle and cycle lane. This creates a definitive location for the bike lane that is more noticeable to vehicular traffic. Examples of this kind of retrofit can be seen in Wateringen, in the southwestern part of the Hague, and in Zwolle; there is also a new construction example in Leidschendam. In the retrofit situations, there was no space available to create a dedicated cycle track separate from the roundabout and so a cycle track inside the roundabout was created as an alternative. A second retrofit treatment is to remove the bike lane and have no marked bike zone at all together, making the roundabout a mixed-traffic roundabout – trucks, cars, mopeds, and cycles – but this can only be done in situations where the roundabout volume does not exceed 6000 vehicles per day.
Bike treatments at Multi-lane Roundabouts
Engineers and designers have a few options for bike treatments at multi-lane roundabouts and they all involve removing bicycles from the facility. The preferred solution is a bicycle underpass. The CROW manual says the underpass is the most “elegant” solution. At a roundabout, there is generally a major street intersecting with a minor street. Due to Dutch planning and design principles, major routes often carry no bike traffic as they do not access any local destinations directly on their route. However, the minor street will usually be a bike route. An underpass can carry minor street bicycle traffic underneath the roundabout.
Two different types of underpasses have been observed in Holland. The first is an underpass directly connecting the two ends of the minor route by tunneling underneath the roundabout – a “straight through underpass.” The second type was found in the “bike-mecca” city of Houten, where a bicycle roundabout was installed beneath the motor vehicle roundabout. This bike roundabout, which had four underpasses – one under each spur approach, was built to link the old north side of town with the new south side of town because there was heavy bicycle traffic coming from all directions. It provides phenomenal connectivity for the bike network and helps mitigate the divisive effects of a major vehicular route cutting through the center of a city.
A second solution is to bypass the roundabout all together. This can be accomplished by using a different route parallel to the roundabout for the bike road or cycle track. This solution is often applied to major through roads. Instead of placing the cyclist in constant contention with the motorist, the approach dictates that the cyclist is moved off the major route completely and shifted to a calmer parallel route, such as a bike boulevard. This approach can be seen in the city of Pijnacker (Click Here) where a turbo roundabout was bypassed completely with a parallel route. The solution benefits both the cyclist and motorist by removing the bikes from the complex multi-lane roundabouts.
CROW Manual Design Guidelines for Roundabout Types
Please click the following link to navigate to the Roundabout Inventory page: