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Network Safety Analysis HD 15
Collision Analysis on the National Road Network
Louise Doherty
NRA, Road Safety Section
Email: [email protected]
Network Safety Analysis HD 15
• Background
• HD-15 process
– Data collection
– Identification of high collision locations
– Network Safety Ranking
– Diagnosis
– Priority ranking
– Implementation
HD 15 Network Safety Ranking
Network Safety Ranking means a method for identifying, analysing and classifying parts of the existing road network according to their potential for safety development and accident cost saving.
European Parliament, 2008
January
February
March
April
May
June
July
August
September
October
November
December
Collision Data
Injury Collisions:
January – December 2005
Exposure to Risk: Population Data
Dublin = 3.5 per 100k
Cork = 7 per 100k
Carlow = 13.5 per 100k
Sligo = 13.8 per 100k
Donegal = 18.4 per 100k
Monaghan = 21.2 per 100k
Road Fatalities (2003 –2005) per
100,000 population by County
Exposure to Risk: Traffic Volume (AADT)
AADT on national roads: 2004
RP - Rural 2 Lane
RP - Motorway RP - Rural Dual Carriageway
RP - Urban Dual Carriageway RP - Urban 2 Lane
Reference Populations on the National Road Network
“Reference Populations are subsets of the Network which have similar features and, as such are expected to have similar safety performances”
European Commission, 2008
Motorway Sites
Rural Dual Carriageway Sites Rural 2 Lane Sites
Urban Sites
Reference Populations on the National Road Network
HD 15 Network Safety Ranking
Identify high collision locations and Network Safety Ranking
• Collision Frequency
– Number of collisions
• Collision Rate
– Ratio of collision frequency to AADT
Calculating Collision Rates
∑ fi ×108 ________________________________________________
365.25 × P × ∑Lj × Qw Rrp =
Where
Rrp = Average collision rate for the reference population
fi = Collision frequency at site j P = Period of analysis in years Lj = Length of section j (km)
Qw = Weighted average annual daily traffic (AADT)
SOURCE: PIARC: World Road Association – Road Safety Manual
2008-2010 Rural 2 Lane Roads
Collision Rate =
Collision Rate = 11.418 per 100 million
(10^8) Veh Km
1183 x 108
365.25 x 3 x 2040.99 x
4632.9
Twice Below = < 5.709
Below = <11.418
Above = >11.418
Twice Above = >22.835
Collision Frequency Vs Collision Rates
Collision Rate
• There is a bias towards low volume traffic
sites.
Collision Frequency
• There is a bias towards high traffic volume
sites.
Below average rate
Twice below average rate
Above average rate
Twice above average rate
Collision Rates
Collision Frequency
Twice below average frequency
Below average frequency
Above average frequency
Twice above average frequency
Collision Cluster Sites
=
+
To help reduce the effect of the
bias inbuilt in both types of
analysis, sites are marked
CLUSTER when both thresholds
are twice above average.
Collision Frequency
Collision Rate
Hazard Sites
Collision Rate Analysis 2008-2010
NRA HD 15 NETWORK SAFETY RANKING
Summary
• Collision data
• Reference Populations
•
• Collision rate
• Collision frequency
