TII GE-STY-01022 - Network Safety Ranking
Network Safety Ranking is a process described in TII Publications under TII GE-STY-01022. Network Safety Ranking uses collision data to rank the safety of national roads and to identify high collision locations on the national road network. The results of this collision analysis go towards targeting annual road safety remedial measures. The EU Directive on Road Safety Infrastructure Management (EU RISM) provides a formal procedure for TII GE-STY-01022, although similar methods have been implemented in Ireland since the 1970’s.
The TII GE-STY-01022 Network Safety Ranking standard can be downloaded here.
Collision Data
Collision data is recorded by An Garda Síochána. This data is used by the Road Safety Authority (RSA) and Transport Infrastructure Ireland (TII) for research purposes. The collision data can be viewed on the RSA Ireland Road Collisions page. TII carries out TII GE-STY-01022 on an annual basis using the latest three years of collision data.
Collision Analysis
Collision data and traffic volume data are used to estimate collision frequency and collision rates for the national road network.
National roads are assigned to one of five reference populations for TII GE-STY-01022 analysis. The roads in each category are of similar type and therefore are expected to have similar safety performances. The average collision rate and average collision frequency is calculated for each reference population.
The national road network is then divided into 1 kilometre sections. The collision rate and collision frequency are calculated for each 1 kilometre section and the results are compared against the average collision rate and collision frequency for the reference population.
The 1 kilometre sections are classified by their collision rate; this is the network safety ranking element of TII GE-STY-01022. High collision locations are the 1 kilometre sections where the collision rate is twice above the average for the relevant reference population and the collision frequency is three or more in the last three years.
Site Visit
Each high collision location is investigated by a site assessment team. Click here to view the qualification requirements for site assessment team members on the TII Publications website.
The records for collisions at high collision locations are thoroughly examined prior to the site visit. This gives details of the types of collisions that have occurred and highlights common factors that explain how the road users failed to cope with their environment.
A site visit is carried out at the high collision locations. The purpose of the visit is to understand the site from the point of view of those involved in a collision and to take note of road features.
The inspection of the site’s collision history, coupled with the site visit, determines if an engineering countermeasure will improve the safety performance of the location.
Ranking and Implementation
The high collision locations that require engineering remedial solutions are identified. The possible options are considered. Each location is ranked against all other similar sites on the national road network. This ranking process is used to target the implementation of road safety remedial schemes.
Evaluation
TII is committed to the evaluation of the road safety remedial measure programmes. The remedial schemes are assessed in terms of the reduction in the number of collisions at the site and the first year rate of return. The evaluation involves a comparison of collision data for the five years before the remedial scheme with the collisions in the three to five year period following the implementation of the remedial measures.
The evaluation reports that have been completed to date are available below:
The Low Cost Remedial Measures Programme. Evaluation of Programme 1 (1994-1995)
The Accident Remedial Measures Programme. Evaluation of Programme 2 (1996-1997)
Road Safety Remedial Measures Programme. Evaluation of Programmes 3-8 (1998-2003)
Road Safety Remedial Measures Programme. Evaluation of Programmes 7-10 (2002-2005)
Road Safety Remedial Measures Programme. Evaluation of Programmes 9-11 (2004-2006)