Network Safety Analysis

TII Publication: TII GE-STY-01022

Network Safety Analysis Process

Network Safety Analysis is a process described in TII Publications under TII GE-STY-01022. Network Safety Analysis uses collision data and vehicle kilometres travelled to assess the safety of national roads and to identify high collision locations on the national road network. The outputs of this collision analysis goes towards targeting annual road safety remedial measures. The EU Directive on Road Infrastructure Safety Management (EU RISM) provides a formal procedure for Network Safety Analysis, although similar methods have been implemented in Ireland since the 1970's. Results from past analyses can be accessed through the TII Open Data Portal. The average collision rates from the most recent analyses are also available here.

The TII GE-STY-01022 Network Safety Analysis standard can be view on TII Publications 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. Validated 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 vehicle kilometres travelled are used to estimate collision frequency and collision rates for the national road network. 

National roads are assigned reference populations for the Network Safety 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 approximate 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.

High Collision Locations are subsequently identified through benchmarking sites against threshold levels (collision rates and collision frequency) established for each specific reference population. Current thresholds used for identifying high collision locations are available here through the Network Safety Analysis Procedures available in TII Publications.

Site Review

Each high collision location is reviewed by a competent review team. The records for collisions at high collision locations are thoroughly examined as part of this process. This information gives details of the types of collisions that have occurred and are used to help establish if any particular collision pattern is evident. This inspection of the site’s collision history, coupled with the site visit where appropriate, helps determines if an engineering countermeasure will improve the safety performance of the location.