Galway Cycling Campaign -Feachtas Rothaiochta na Gaillimhe

Irish Junction Design Practice

An Information Sheet

What's the issue?

Up to 75% of car/cycle collisions happen at junctions.  In Ireland RT181 Geometric Design Guidelines: Intersections at Grade has been the standard design guidance for 17 years.  There is evidence suggesting that for priority junctions RT181 is based on both a philosophy of design and the use of actual designs that are associated with increased risk of collisions [1] .   In particular there is evidence suggesting that junctions constructed to this standard are likely to be associated with increased risk of the most common types of car/cycle collision [2] .  Concerns have arisen regarding both the visibility parameters specified by RT181 and on the issue of the recommendations regarding kerb radii.  Our model system is the T-junction, which accounts for the majority (40%) of junction collisions.  However the issue may apply to other priority intersection types and particularly to roundabouts.  The national authorities were first made aware of this issue in 1998 but so far have failed to provide any response.

Junction collisions

Cyclists who fail to yield, overtake on the left or who use cycle lanes are at increased risk of collision.  However, the majority of car/cycle collisions at junctions involve motorists who fail to yield to lawfully proceeding cycle traffic.  These collisions have been associated with excessive visibility envelopes and also with large entry dimensions, (kerb radius + lane width).  This is not just an issue for cyclists, research has identified length of stopping sight distance on all arms as a multiplying factor for several types of accidents.   1) On major left arm, increased accident risk for right turn from the major with major left to right accidents 2) On major right arm, increased risk for right turn from the minor with major right to left accidents 3)  On the minor arm, increased risk for two types of accidents: right turn from the minor with major left to right accidents and for left turn from the minor with major right to left accidents [1] .

Visibility parameters

Current UK guidance is to specify minimum and maximum visibility parameters for priority intersections [3] .  In addition a separate visibility envelope is specified for the immediate area of the junction.  Maximum (not to be exceeded) visibility parameters are set out because long sight distances are associated with excessive entry speeds and consequently with increased risk of collisions.  Sight triangles exceeding 9 x 25m have been associated with increased risk of car/cycle collision.  In the UK a "Desirable Minimum Stopping Sight Distance" to the junction is provided to allow "drivers time to slow down safely at the junction, or stop, if this is necessary".  However, UK guidance expressly cautions that "increased visibility shall not be provided to increase the capacities of various turning movements".  Irish design guidance an apparently opposing philosophy is seen where visibility is provided which permits a minor road driver "to turn into or cross the major road without stopping".  Irish guidance only allows for minimum sight distances and by implication encourages the use of large visibility envelopes.  

Kerb/corner radii

The Galway Cycling Campaign is still seeking satisfactory guidance on the general issue of kerb radii (curvature).  There is guidance recommending radii of less than 6m on intersections with cycle routes [4] .  Large entry half widths (lane +kerb radius >10m) are reported as being associated with increased risk of car/cycle collision.  It should be taken as a general principle that the indiscriminate use of large kerb radii (>4m) in urban areas can only add to the general hostility of the traffic environment for vulnerable road users, including pedestrians.  Despite these concerns Galway corporation has chosen to specify minimum radii of 6-10m regardless of the mix of traffic.

Defensive action for cyclists

The best defensive action for cyclists is to adopt a prominent road position when passing side roads/roundabout entries, always try to stay well clear of any yield/give way markings [5] .  Even if you wear high visibility clothing, assume that you will not be seen unless you're also positioned where other drivers are looking.   However, be prudent, particularly on faster roads and at night.  In congested conditions resist the temptation to overtake on the left.  If you choose to use cycle paths/lanes then be aware that they increase your risk of being hit by a car.

© Galway Cycling Campaign, February 2001

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