COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF TERENURE-RATHFARNHAM AREA COMMITTEE 1

Tuesday, December 04, 2007

HEADED ITEM NO. 6

RIGHT TURN BAN SPRINGFIELD AVENUE

The traffic section has completed its findings of the analysis of the Templeogue Road and Springfield Avenue junction. Two scenarios as follows were tested.

(1) Existing layout, right turn ban to Springfield Avenue in place, with a bus lane / left turn lane and a straight ahead lane provided.

(2) Right turn permitted and lanes altered thus: a combined ‘bus lane, left turn lane and straight ahead lane’ and right turn lane.

Comparison of the results for the existing and modified junction showed the following:

• The provision of a right turn lane would confine all the other traffic (left turning, straight ahead and bus traffic) into one lane.
• There would be less straight ahead and left turning traffic accommodated at the junction. This would result in traffic queueing back into Templeogue village.
• Journey times for buses would be increased due to additional congestion in the village.
• A new phase is required to permit the traffic to make the turning movement removing ‘green time’ from the remaining movements.
• The provision of the right turn would increase the amount of traffic using Templeogue Village in order to access the turn.
• The associated congestion would have a negative impact on the environment of the village.

In summary in light of the above, it is recommended that the right ban is retained.

Analysis

The data fort this report was analysed on two models, firstly a network model was used to calculate the effect the removal of the right turn ban would have on traffic flows and the potential demand for the turn. This model provided a data set for the junction analysis which looked more closely at signal operation for the two models.

Network Model

The network model used to calculate the traffic flows is the same model the DTO use for modelling changes in the Dublin road network.

“5 Conclusions

5.1.1 The Local Area Traffic Model developed for South Dublin County Council was used to assess the removal of the right-turn ban from Templeogue Village onto Springfield Avenue. SATURN is a predictive modelling tool and uses an ‘equilibrium’ technique based on an optimum combination of all-or-nothing assignments, so that for a given Origin-Destination pair a range of routes is normally used but each has the same minimum Origin-Destination cost.

5.1.2 The output from the model has used the Pessimistic matrix in the assessment works as it best met the counties employment scenario. This is based on a slower rate of growth in the South Dublin Region in terms of employment and population.

5.1.3 The analysis of this option was undertaken based on a comparison of traffic flows around Springfield Avenue, via network wide summary statistics from the traffic model and select link analysis techniques. The option has been compared against the 2016 DM network.

5.1.4 Option DS1 reduces the actual flow on Templeogue Road to the north east of the Templeogue Road/Templeville Road/Springfield Avenue junction and increases traffic levels on Springfield Avenue itself.

5.1.5 The overall results demonstrate that the implementation of the removal of the right turn ban would have a negative impact on the overall network performance. There is a deterioration in the overall network performance equating to an additional 171 pcu hrs of overall network travel time and 516 km of overall travel distance in the network in the one hour period modelled.

5.1.6 A select link analysis has been carried out on the right turn from Templeogue Road to Springfield Avenue which shows that 169 vehicles could potentially use this right turn if the existing ban was removed. This equates to approximately 19% (169 of 896 vehicles) of the total eastbound flow on Springfield Avenue.

5.1.7 It is recommended that the removal of the right turn ban at the Templeogue Road/Templeville Road/Springfield Avenue junction is assessed more fully using the appropriate traffic signal program. This will have the effect of optimising the signal timings which should avoid the increases in traffic flows on Wainsfort Road and Fortfield Road that the SATURN model is predicting.

5.1.8 From a SATURN traffic forecasting viewpoint the removal of the right turn ban from Templeogue Road onto Springfield Avenue shows an increase of 66 vehicles between the DM and DS1 options however the total level of traffic that could potentially use the right turn if the ban was lifted is 169 vehicles. The difference is due to the fact that a redistribution of traffic occurs across the network when the ban is removed.

5.1.9 SDCC will have to come to a view on whether to proceed with the removal of the right turn ban after taking into account other factors that may come into play regarding the increase in flows on Springfield Avenue e.g. increase in noise and pollution levels and also whether a right turn lane can be provided without prejudicing bus priority and straight ahead traffic movements.”

Junction Model

From the network model the signals were analysed for an increase of 19% in traffic volume representing the right turning traffic. This was compared to a current scenarios model of the junction.

For the existing arrangement the PRC (practical reserved capacity) for the junction is 23%, this indicates the junction works within its capacity. If the PRC drops below 10% the junction is considered to be congested as it will tend to block approaching traffic.

For removal of the ban and the introduction of the right turn lane and signal the PRC dropped to -14% (minus 14%) i.e. the traffic demand exceeded the theoretical maximum capacity for this junction. The model reports the traffic needs to be reduced by 16% for the junction to operate

“Unable to find a cycle time for which the junction is within capacity because the junction is heavily overloaded.

Flows must be reduced by 16 percent.”