iRAP Road Attribute Risk Factors
Facilities for Bicycles
This factsheet describes the road attribute risk factors used in the iRAP methodology for Bicycle Facilities.
Facilities for Bicycles records the presence of purpose-built facilities for non-motorised vehicles.
About road attribute risk factors
Road attribute risk factors, sometimes called crash modification factors (CMF), are used in the iRAP Star Rating
methodology to relate road attributes and crash rates. Risk factors (or CMF) are described by the Crash Modification
Factor Clearing House as follows:
A crash modification factor (CMF) is a multiplicative factor used to compute the expected number of crashes
after implementing a given countermeasure at a specific site.
For example, an intersection is experiencing 100 angle crashes and 500 rear-end crashes per year. If you
apply a countermeasure that has a CMF of 0.80 for angle crashes, then you can expect to see 80 angle
crashes per year following the implementation of the countermeasure (100 x 0.80 = 80). If the same
countermeasure also has a CMF of 1.10 for rear-end crashes, then you would also expect to also see 550
rear-end crashes per year following the countermeasure (500 x 1.10 = 550).
Related documents
This factsheet should be read in conjunction with:

iRAP Methodology Fact Sheets (http://irap.org/about-irap-3/methodology).

Star Rating and Investment Plan Coding Manual (http://irap.org/about-irap-3/specifications).

Road Safety Toolkit (http://toolkit.irap.org).
Risk factors
Risk factors by road attribute category, road user type and crash type
Facilities for Bicycles
Bicyclist likelihood along
Bicyclist likelihood
intersection
Bicyclist severity
along
Segregated bicyclist path with barrier
0.0
1.0
0.0
Segregated bicyclist path without barrier
0.1
1.0
90
Dedicated bicyclist lane on roadway
12
1.0
90
None
20
1.2
90
Extra wide outside (≥4.2m)
17
1.2
90
Signed shared roadway
19
1.0
90
Shared use path
1.0
1.0
90
Facilities for Bicycles
Bicyclist likelihood along
Bicyclist likelihood
intersection
Bicyclist severity
along
Paved shoulder >= 2.4m
16
1.2
90
Paved shoulder 1.0m < width < 2.4m
17
1.2
90
Paved shoulder 0m < width<= 1.0m
18
1.2
90
Selection of risk factors
The risk factors describe a wide range of risk situations.
Elvik and Vaa (2004) are cautious in their expectation of the benefits of bicycle facilities and show crash modification
factors in some work of greater than 1 (that is, crash rates increase). This is repeated in several studies from the CMF
Clearing House and justifications of benefits are likely to have been based on assessment of large-scale networks and
to be relatively few in number. The picture is complicated by the fact that demand may go up if a bicycling facility is
provided. The increase in exposure does not lead to a proportional increase in risk and a “safety in numbers” effect
has been identified by Turner et al (2006).
Work by SWOV 2012 reviewed this topic, and commented as follows:
“A separate bicycle track is preferable for distributor roads, because the large degree of separation offers the
best possible protection against the large speed differences between motorized traffic and cyclists. Not only
the separate bicycle track, but also the measure moped on the carriageway is a way to separate fast and slow
traffic, mopeds and bicycles in this case. This measure, which has been operational since late 1999, involves
mopeds using the carriageway on roads with a speed limit lower than 70 km/h. Another guideline for the
application of bicycle facilities (CROW, 2006) is that they should not be located adjacent to parking spaces so
that conflicts between parking vehicles (manoeuvres, doors opening and passengers getting out) and passing
cyclists are avoided. Finally, a one-way bicycle track is to be preferred to a two-way bicycle track (CROW,
2006). A crash analysis carried out by the Dutch Centre for Transport and Navigation DVS (Schepers &
Voorham, 2010) shows that the risk of an intersection crash is also greater on a two-way bicycle track than on
a one-way track. When a two-way track is indeed chosen, compensatory measures like speed humps are
required at those locations where bicycle tracks cross the carriageway (CROW, 2006).”
“...we already concluded that bicycle facilities appear to have a positive road safety effect on road sections of
urban distributor roads. No recent data, however, is available about the safety level of the different types of
bicycle facilities on these road sections.”
On the basis of research from the 1980s (Welleman and Dijkstra, 1988) and taking account of the fact that mopeds no
longer use the bicycle track, Wijnen, Mesken and Vis (2010) estimate that the construction of a separate bicycle track
results in a 4.4% reduction in the number of injury crashes. This refers to a reduction in all types of crashes (also
those not involving bicyclists), and to urban distributor roads with a separate bicycle track as opposed to the types of
road without a separate bicycle track or parallel road. Welleman and Dijkstra (1988) furthermore concluded that
bicycle lanes were less safe than no bicycle facility. Unfortunately it is not known whether this is still the case and
whether this applies to all construction types of bicycle lanes. There are indications that for busy rural distributor roads
with many connections it is safer to construct a parallel road than a bicycle track, but this requires further investigation
(Godefrooij et al. 2008).
Turner et al (2009a) comment “Studies conducted to compare the crash rates for on- and off-roadway cycling have
shown that footpaths are much less safe than other on- or off-roadway cycling options, with data indicating that
footpath cycling is 1.8 to 2.5 times more dangerous than cycling on the roadway, and 8 to 11 times more dangerous
than cycling on an off-roadway track (with very few or no driveways or vehicle crossings). In Denmark, before-andafter studies of off-roadway cycle paths were undertaken over a period of three years. The results showed that cyclist
casualties increased 48% following introduction of off-roadway cycle paths. In addition, vehicles, moped riders and
pedestrians suffered more crashes, with an overall rise in casualties of 27%. These footpath dangers arise principally
from conflicts with motor vehicles, pedestrians and other cyclists.”
For the iRAP model, comparing facilities, as a baseline, it is assumed that on a segregated bicycle path there is zero
risk of vehicle versus bicycle crashes. On a segregated bicycle path with a barrier it is recognised that there is a small
possibility of a crash with a motorised vehicle if that vehicle has left the carriageway. Signed, shared roadways are
expected to have relatively little benefit, with increasing benefit provided by increasing width of paved shoulder and a
step change in improvement if a dedicated bicyclist lane is provided on the roadway.
Background research and model development
In outlining the research on which earlier versions of the iRAP model was based, Lynam (2010) reported that initially
these risk factors have been assumed to have a similar effect on bicycle crashes as the motorcycle facilities have on
motorcycle crashes. Elvik and Vaa (2004) suggested there was little evidence that cycle tracks reduced bicycle
crashes, but this appears mainly due to the increased cycle flows they encourage so the risk per cyclist should reduce.
They suggest physically separating bicyclists onto a separate pavement reduces bicycle crashes by 30%, but cycle
lanes on the road only reduce cycle crashes by a very small percentage. Cycle lanes through signalised junctions
reduced cycle crashes by 12% but increased vehicle crashes by 39% leading to an overall increase in total crashes of
14%.
Turner et al (2009) assessed the effectiveness of different cycle facilities. A review of on-road facilities based on
overseas research indicated crash reductions for cyclists of between 35 and 50%, although some studies actually
detected an increase in crashes (perhaps due to inadequate widths of lanes). An analysis of New Zealand data
indicated only a 10% reduction in cycle crashes from the use of on-road cycle lanes. Again this recent research will
be used to inform any future revision of the risk factor described here.
Rating risk on a dedicated bicycle lane implies the same risk patterns as experienced on-roads. In some
circumstances this is not a good description of risk. For example, in this and other situations, it may exaggerate the
threat to life during run-off crashes.
Risk factors in earlier versions of the iRAP model
Facilities for Bicycles
Bicyclist likelihood along
Segregated bicyclist path with barrier
1.0
Segregated bicyclist path without barrier
1.0
Dedicated bicyclist lane on roadway
1.5
None
2.0
Primary references
The following publications are the primary references used in the selection of the iRAP road attribute risk factors. A
complete list of citations is available in: iRAP Road Attribute Risk Factors: Full Reference List.
Elvik, R, Hoye A, Vaa, T, and Sorensen, M. (2009). The Handbook of Road Safety Measures, Second Edition (2009)
Emerald Group Publishing Limited. ISBN 978-1-84855-250-0.
Lynam, D (2012). Development of Risk Models for the Road Assessment Programme. RAP504.12 and TRL Report
CPR1293, Published by iRAP and TRL and available at: http://www.trl.co.uk and at http://www.irap.org.
Mak, K. and Sicking, D. (2003). Roadside Safety Analysis Program – Engineer’s Manual. Transportation Research
Board (TRB) National Cooperative Highway Research Program (NCHRP) Report 492. ISBN 0-309-06812-6.
Turner, B. Steinmetz, L., Lim, A. and Walsh, K. (2012). Effectiveness of Road Safety Engineering Treatments. APR422-12. Austroads Project No: ST1571.
Turner, B., Affum, J., Tziotis, M. and Jurewicz, C. (2009). Review of iRAP Risk Parameters. ARRB Group Contract
Report for iRAP.
Turner, B., Imberger, K., Roper, P., Pyta, V. and McLean, J. (2010). Road Safety Engineering Risk Assessment Part 6:
Crash Reduction Factors. Austroads AP-T151/10. ISBN 978-1-921709-11-1.
University of North Carolina Highway Safety Research Center and U.S. Department of Transportation Federal
Highway Administration (2013). Crash Modification Factors Clearing House: http://www.cmfclearinghouse.org/.
17 July 2014