This post is by Dr. Hank Weiss, an injury epidemiologist with
over 3 decades experience in injury prevention research and
practice, and a SPOKES member.
uni-directional separated/protected bike
are the safest on-road design
when they cross driveways and intersections
Recently, a New Zealand Transportation
Agency (NZTA) and Dunedin City Council (DCC) staff working
released an ‘update report’ describing options for
separated cycle lanes along the dangerous SH1 one-ways in the
Central City. Just getting underway is a period of public comment as NZTA begins
reviewing the preferred options. The report recommends two
options for further consideration. Both options offer people
who cycle greatly enhanced mid-block vehicle protection from
being hit from behind and car door hazards. However, there
are important differences that arise for each.
Option 1 – The first option features a
uni-directional (one-way) 2.6m separated cycle
lane Separated Bicycle Facility (SBF) on the
right-hand side of each of the SH1 one-way streets,
with cyclists riding in the same direction as the traffic
(both mid-block and intersection example profiles shown
below). This was the top option favoured by the working
Example uni-directional mid-block
Example uni-directional intersection profile (barriers
do not go through intersection).
2) The second option entails a
3.2m bi-directional (two-way) separated cycle
lane SBF along Cumberland Street with cyclists riding in
two-way formation along the right side (both mid-block and
intersection example profiles shown below).
Example bi-directional mid-block profile.
Example Bi-directional intersection profile (barriers
do not go through intersection).
Safety Rationale for
I wish to focus on the safety advantages of Option 1, the
uni-directional separated cycle lane. To do so, I will
revisit SPOKES’ earlier discussion of the findings from a
Canadian study and a recent further analysis of these data. I
also draw from a recent cycle tracks safety review paper
(Thomas et. al, 2013).
SPOKES blog readers will recall that Teschke et. al (2012) found much greater
safety on Canadian cycle tracks when compared to cycling on
major streets with only painted bike lanes or no bike
infrastructure at all. They found, for example, that cycle
tracks were about six times safer than unprotected
bike lanes with parked cars, and nine times safer than
streets with parked cars and no lanes or
Bike lanes with vehicle parking were about 7 times
riskier than fully protected lanes.* In the second peer-reviewed paper from this
study, more attention was paid to road section types and what
settings and configurations were safer than others.
When cyclists arrive at an
intersection from the opposite direction to traffic in
two-way situations (option 2), most studies show the crash
and injury risk goes up substantially. The difference
was statistically significant in
Harris’ et. al. analysis of protected cycleways. In their
multiple regression model, the opposite direction scenario on
tracks with intersections resulted in a large elevated risk
ratio of 7.8 (95% CI = 2.0-30.3) compared to uni-directional
Astute observers will find online references to some older European
studies (for example, [Jensen, 2008] suggesting that protected cycle
tracks might be less safe than unprotected bike lanes. Such
findings, however, were based on older studies that: a)
combined either shared pedestrian paths and protected tracks
or uni-directional and bi-directional protected tracks into
single analytical categories, b) used absolute numbers
instead of rates, c) did not take injury severity into
account, or d) had statistically insignificant results. When
uni-directional protected cycle tracks are analysed
separately they stand-out as the best option for reducing
serious injury (Thomas et. al, 2013). In summary,
properly designed uni-directional separated/protected bike
lanes are the safest on-road design when they cross driveways
Intersection considerations and design treatments are
important for all types of cycle infrastructure because about
60% of bike/motor vehicle crashes occur at intersections. A
protected track in the same direction as the traffic doesn’t
appear to add any more intersection risk than unprotected
lanes (they essentially become unprotected lanes at
intersections because turning cars must cross them). But
adding new protected lanes creates the opportunity for
improving safety even more by upgrading intersection designs
to modern practice. Key concepts to improve cycle
intersection crossings include the following (adapted from
Cycle Toronto and Thomas et al.):
- At intersections, bring the cycle track closer to
parallel traffic for visibility.
- Place a motor vehicle traffic stop line at least 20m
- Mark cycle crossings through the intersections (just as
crosswalks mark pedestrian paths).
- For unsignalised intersections, where the cycle track is
along the priority road, it can help to keep cycle track
elevated through the crossing (essentially a speed hump).
- At signalised intersections, (1) traffic signals can be
limit conflicts between cyclists and turning cars. Where
are not entirely eliminated, (2) use of geometric measures
tight corner radii, medians and speed humps can help ensure
traffic moves slowly. With years of trial and error, many
consider the Dutch Junction
design state of the art.
- Modern technology allows signals that can control the
when the time that it is safe for bikes to cross differs
from the time
that the parallel traffic phase is green.
- Reduce the number of motor vehicle turns across the cycle
offering parking on the opposite side and limiting cross
by time, vehicle type or place.
- Eliminate bus/cycle conflicts by opposite road side
separation (as chosen for both Dunedin SH1 options).
Winner: Strongly in favour of Uni-directional
Conflicts between cyclists from
vehicles turning into driveways will remain mostly
unchanged with the uni-directional option unless the right
side of the street has more or fewer driveways than the
currently used left side. The removal of parked cars,
however, has the extra benefit of improving motorist
visibility of cyclists and pedestrians while turning
into driveways. It is hypothesised that a bi-directional
track could lead to some drivers overlooking the contra-flow
cycle traffic during drive-way manoeuvres, but to our
knowledge this has not been quantified. Removal of parked
cars from alongside the cycle track will also reduce
existing hazards by opening up sight-lines between
vehicles pulling out of drive-ways and cyclists.
Various means of signage and elevated entries can help
further improve awareness during driveway manoeuvres.
Winner: In favour of Uni-directional option
3. Right-hand intersection or driveway turns
right-hand lane placement on the one ways for both options
may offer increased motorist visibility of cyclists during
vehicle right-hand turns since the driver will now be on the
same side of the vehicle as the cyclist, reducing vehicle
However, we are not aware of studies that have quantified
this. On the other hand, with a larger turning radius,
right-hand vehicle turns may obtain higher speeds which could
negate visibility benefits. It is unknown how these factors
might be different for cycle traffic moving in the same or
opposite direction. Intersection studies suggest on first
principles that it will be better for uni-directional cycle
travel. We have talked to a road engineer in San Francisco
where an opposite side uni-directional buffered track has been
in place and they reported no particular turning issues.
Overall Safety Winner: Option 1 –
Uni-directional separated lane