Galway Cycling Campaign -Feachtas Rothaiochta na Gaillimhe

Multilane Roundabouts

An Information Sheet

© Galway Cycling Campaign, February 2001

What's the issue?

Despite the existence of serious reservations [1] the character and fabric of many Irish towns has been drastically altered, some would say systematically destroyed, by the use of multilane roundabouts of a design that is demonstrably hostile, dangerous and inappropriate.  For pedestrians, cyclists, motorcyclists and many motorists, these junctions are the most loathed and feared locations on the roads network.  On multilane roundabouts of the design specified by Irish guidance manuals cyclists have an injury accident rate that is 14-16 times that of motorists.  Motorcycle/Scooter users are only marginally better off at 10-13 times the injury rate.  Roundabouts represent one of the major deterrents to increased cycle use in Ireland.  They are also a major obstacle to the development of a modern integrated transportation infrastructure.

But aren't large roundabouts needed to cope with heavy city traffic?

No, an uncontrolled roundabout actually has a lower peak capacity than an equivalent signalised junction.  In congested conditions roundabouts get "locked up" by one dominant, stalled, traffic stream.  Roundabouts are incompatible with modern urban adaptive traffic control systems, which manage traffic in response to changes in demand.  They are also incompatible with modern bus priority systems, which use detectors and traffic signals to give priority to buses [2] .  In urban areas the main justifications for multilane roundabouts are 1) they are favoured by property developers because it is thought they give a better impression to property investors [3] .  2) they give motorists the illusion of reduced delay at off peak times, this is obtained at the expense of increased traffic as cyclists and pedestrians are forced off the roads 3) they incur lower annual running costs than traffic signals (but require more land).

Solutions to roundabouts

There is a hierarchy of measures available for dealing with multilane roundabouts, 1) replace with signalised intersection, 2) install full time signal control on the roundabout, 3) physically change roundabout geometry, the latter two options may be combined.  Recommended geometric modifications include changes to entry/exit layouts, circulatory lanes and visibility parameters.  A "radial" format is used, with entry/exit lanes made perpendicular, rather than tangential, to the central island by removing flares and modifying splitter islands.  A narrowed circulatory lane is used and/or separate lanes are marked.  If enforceable, there may also be scope for the application of special speed limits on roundabouts.  The established concerns about wider Irish junction design practices and excessive vehicle entry speeds are also relevant to roundabouts [4] .  Irish design practice requires that entering drivers be given a clear view of the roundabout conditions from at least 15m back [5] .  It is suggested elsewhere that roundabouts with stopping sight distances of 15m or more could lead to drivers misjudging the speeds of traffic, including cyclists, already on the roundabout [6] .  

These might be seen as excessively involved and expensive solutions by some.  However the essential point is that the use of high-flow roundabouts in urban areas has been an expensive mistake.  Their use is incompatible with integrated transportation systems, involves a loss in peak hour capacity and is also a direct cause of increased motor traffic and traffic congestion.  Finally in Galway, large roundabouts have been associated with up to tenfold increases in the number of material damage crashes between cars [7] .  This suggests that they also represent a serious financial burden on the city's motorists.

Defensive action for cyclists.

The Irish authorities have been aware since at least 1987 that there is likely to be little or no scope for the use of segregated facilities at roundabouts.  The predominant type of car / cycle collision on roundabouts involves entering motorists crashing into circulating cyclists.  The recommended tactic for collision avoidance is for cyclists to adopt a prominent position within the main traffic stream and negotiate the roundabout in exactly the same manner as someone in a car [8] (this was the original function of the ghost islands on roundabout splitter islands [9] ).  It is our understanding that Swiss Federal traffic law has now been changed to facilitate cyclists in staying within the main traffic stream.  Conversely, logic dictates that a cyclist who attempts to circulate outside the main traffic stream by using a cycle lane will experience an increased risk of collision.  This is confirmed by the recent experience of Dorset county council who marked such "annular ring" cycle lanes on several roundabouts, apparently without prior consultation [10] .  These are now being removed following a doubling of the casualty rate.  However don't tackle roundabouts unless you are very sure of yourself and your bicycle.  If you aren't sure then dismount and walk.

Bypasses

There is the issue of constructing cyclist bypasses around large roundabouts.  Where adequate land is available this might be thought an attractive option.  However such bypasses are of most benefit to left-turning cyclists, who already have the least problems at roundabouts.  Cyclists going straight on or turning right suffer the most inconvenience at roundabouts.  These are likely to experience substantially increased delays on bypass systems and so be deterred from using them.  When a bypass system using back streets was provided around the Elephant and Castle roundabouts in London 63%-75% of cyclists continued to use the main road [11] .  We understand that a similar situation obtains at the Artane Roundabout in Dublin.  This is not intended to dismiss the use of bypass systems but merely point out that in urban areas they are not an alternative to removing/modifying roundabouts.  

© Galway Cycling Campaign, February 2001

The Galway Cycling Campaign can be contacted c/o the One World Centre, The Halls, Quay St, Galway