A
road traffic model was built which covered both the northern and
southern sections of the route corridor. Existing data from origin-destination
surveys, carried out at six locations during 1997 and 1998 and new
data collected in March / April 2001 were used to provide a base
year trip matrix.
Forecasting of traffic growth was carried out in accordance with
the methods used in the National Roads Needs Study for a design
year of 2022. In addition, an estimate was made of the potential
transfer of longer distance trips to the N9/N10 corridor from other
parallel corridors, as a result of construction of the scheme. A
number of initial routes were tested. These routes included routes
close to the N9 and N78 and bypasses to the east and west of Carlow.
Further south the tests included a route close to the N9 (Thomastown)
corridor and a route close to the N10 towards Kilkenny.
Further tests were carried out during the route selection process,
to evaluate the effects of a route following the N9 corridor (Route
9) a route following the N78 corridor towards Athy (Route 10) and
a route following the N9 (Thomastown) corridor (Route 11).
The conclusion reached was that an eastern bypass of Carlow had
advantages in traffic terms. An eastern bypass could easily distribute
the traffic around Carlow with junctions on the N9 to the north
and south of Carlow Town. Traffic from a western bypass would overload
the N80 to the west of Carlow Town and would cause circulation difficulties
within the Town. Junctions were located to serve Athy and Paulstown
and on the N80 east of Carlow to serve County Wexford.
Movements to and from Kilkenny were shown to be crucial in the traffic
assignments and there was clearly a benefit in route options which
passed close to Kilkenny.
Access to Kilkenny was also an important factor in the location
of proposed junctions. It had been concluded from the traffic analysis
that junctions should be provided to the east and south of Kilkenny
(in both cases close to the N10) and that a new single carriageway
link should be added between the new junction on the east side of
Kilkenny and Kilkenny City (linking to the ring road). Thomastown
would best be served by a new junction in the vicinity of Knocktopher
and an additional junction was planned at Mullinavat to serve the
local community rather than for overall strategic reasons.
The economic benefits of the route options were compared using the
UK COBA (Cost Benefit Analysis) programme using default parameters
calculated for Irish conditions. The results showed Benefit to Cost
ratios in the range of 1.66 to 2.11 and these were used to compare
the relative economic performance of the various options.
