M17/M18 - Gort to Tuam [open to traffic]

Dear Mr. xxx,

In your email of the 16th December, 2009, you expressed 3 main concerns regarding the design of the junction and also commented on the proposed Motorway Service Area access:

1. ‘Underpowered’ – You appear concerned that large traffic volumes on the M6 Galway to Dublin motorway and the M17/M18 Limerick to Tuam Motorway will limit the capacity of the junction;
2. ‘Difficult to upgrade’ – You also expressed concerns that the proposed junction will create difficulties if the junction was to be upgraded to a full free-flow junction such as a cloverleaf, partial cloverleaf, 4-level stack or similar; and
3. ‘An apparent attempt to save money by using a small land footprint’.

In May 2004, McCarthy Hyder Consultants Ltd in association with PJ Tobin & Co Ltd, prepared a ‘Junction Strategy Report’ to assess junction options for the 3no. junctions along the N18 Oranmore to Gort Scheme – namely Gort Junction, Kiltiernan Junction and Rathmorrissy junction. For the Rathmorrissy Junction there were 6no. options considered, including, dumbbell type junction (two level), oval roundabout junction (two level), oval roundabout junction with free flow slip lanes (three level), free flow clover leaf junction, roundabout junction (three level) with free flow left turn lanes (360m diameter) and roundabout junction (three level) with free flow left turn lanes (240m diameter). It was concluded in the report that the roundabout junction (three level) with free flow left turn lanes (240m diameter) be recommended as the preferred junction and it was this junction that was taken forward to preliminary design and through to the EIS and approved by An Bord Pleanála. While land take issues were considered in the junction selection, it was not the determining criteria. Junction performance and safety issues were also assessed in conjunction with the overall cost of the junction.

The proposed Rathmorrissy Junction comprises a three level junction with:

1. The M6 Galway to Dublin Motorway unimpeded through the junction on the lower level;

2. The M18/M17 Limerick to Tuam Motorway unimpeded through the junction on the upper level;

3. Free-Flow unimpeded left turn slip lanes on all four arms:

i. M18 from Limerick – M6 to Galway;
ii. M6 from Galway – M17 to Tuam;
iii. M17 from Tuam – M6 Dublin;
iv. M6 from Dublin – M18 to Limerick.

4. Slip Roads off the mainline motorways to a roundabout on the middle level serving the right turn traffic movements of:

i. M18 from Limerick – M6 to Dublin;
ii. M6 from Galway – M18 to Limerick;
iii. M17 from Tuam – M6 to Galway;
iv. M6 from Dublin – M17 to Tuam.

The traffic flows (at year of opening) published in the EIS for the M17 Galway to Tuam scheme is summarised below:

[see attached image]

You make reference to 50,000 vehicles per day (at opening) passing through the junction, however it should be noted it is only the right turn traffic movements that will interact with the proposed roundabout junction. In addition, the right turning peak hour flows will be tidal, where by in the AM, the peak right turn will be the M17 from Tuam – M6 to Galway and in the PM, the peak right turn will be the M6 from Galway – M18 to Limerick.

An analysis of the operation of the roundabout has been undertaken using ARCADY (a widely accepted computer program used to model the operation of roundabouts). The analysis indicated that in the peak hour in the design year (20 years after opening), the roundabout will comfortably accommodate the predicted traffic flows with ample spare capacity. In the event that traffic flows do increase significantly greater than those predicted, the layout of the roundabout will accommodate traffic signals (should such remedial measures be required to improve traffic management) since the spacing between adjacent entry / exits are sufficiently large to accommodate vehicle storage.

We note your comment that the roundabout junction was only specified to provide access to a proposed Motorway Service Area. However the decision on a possible motorway service area was made well after the decision to continue with the roundabout junction (three level), as demonstrated by the timeline listed below:

· May 2004 – Issue of N18 Oranmore to Gort – Junction Strategy Report – recommending the roundabout junction (three level) with free flow left turn lanes (240m diameter) as the preferred junction arrangement;

· In 2005 the Authority was requested by the Minister for Transport to undertake a review of policy with regard to the provision of service areas on motorway and high quality dual carriageway sections of the national roads network;

· The Authority announced in September, 2006, the decision to secure directly, through the PPP mechanism, on-line service areas was accompanied by a map indicating the intended locations of the priority service area facilities to be procured on the major inter-urban routes, including the M6 at the M6/M17/M18 junction.

· In October 2007, the NRA published ‘Policy for the Provision of Service Areas on Motorways and High Quality Dual Carriageways’ and included in this document was a preferred service area location at the M6/M17/M18 junction;

I trust the above addresses your queries and concerns.

Regards