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.
Properly designed uni-directional separated/protected bike lanes
are the safest on-road urban design
when they cross driveways and intersections
Recently, a New Zealand Transportation Agency (NZTA) and Dunedin City Council (DCC) staff working group 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 group.
Figure 1. Example uni-directional mid-block profile.
Figure 2. 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).
Figure 3. Example bi-directional mid-block profile.
Figure 4. Example Bi-directional intersection profile (barriers do not go through intersection).
Safety Rationale for Recommended Priorities
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 infrastructure. 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. In Harris’ et. al. analysis, the opposite direction scenario at intersections resulted in a large elevated risk ratio of 7.8 (95% CI = 2.0-30.3) compared to uni-directional tracks.
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 and intersections.
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 before intersections.
- Mark cycle crossings through the intersections (just as crosswalks mark pedestrian paths).
- For unsignalised intersections, where the cycle track is running along the priority road, it can help to keep cycle track and footpaths elevated through the crossing (essentially a speed hump).
- At signalised intersections, (1) traffic signals can be used to limit conflicts between cyclists and turning cars. Where those conflicts are not entirely eliminated, (2) use of geometric measures such as tight corner radii, medians and speed humps can help ensure that turning 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 cycle track 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 track by offering parking on the opposite side and limiting cross traffic turns 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 option
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
The 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 blind spots. 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.
4. Usable Road Width
A two-way cycle lane will take up more width along the road way right-of-way, while typically allocating less room per lane of cycle traffic. This has safety ramifications for all road users. In the mid-block profiles proposed above, for each lane of cycle traffic the bi-directional lane allocates 1.6m vs 2.6m for the uni-directional lane. Therefore, the uni-directional lane allows for passing without concern for oncoming cycle traffic, has more room for passing, and offers more comfortable and social riding. In addition, the greater overall width of the bi-directional option (3.2m vs 2.6m) means narrower lanes for motor-vehicles, since the extra width has to come from somewhere (if the road is not widened to accommodate it).
Winner: In favour of Uni-directional option
Overall Safety Winner: Option 1 – Uni-directional separated lane
Editors Note: Section 4 was added November 29 and the last photo switched-out
Take Action NOW!
SPOKES urges its members, friends and all concerned citizens to consider the options outlined in the NZTA/DCC report and consultation website and support the need for some form of separated lanes. If you agree with the above safety analysis for the recommended uni-directional option, we encourage you to mention that as well. SPOKES has made it very easy to quickly do this on our own Submission Website.
*Other recent studies also show the relative safety of separated cycle tracks:
- 3 cycle tracks in NYC showed a decrease in total cyclist injuries: 9th Ave: -57%; 8th Ave: -30%; Prospect Pk West: -62% (NYC Department of Transportation).
- Sevilla, Spain: Construction of 164km of cycle tracks led to a halving in cyclist serious injury rate per 100,000 trips from 2006 to 2010 (personal communication via John Pucher from Ricardo Marqués, Universidad de Sevilla).
- In a study of 19 cycle tracks in the USA, the average injury rate per million bike km was much lower on cycle tracks (2.3) than on roads without cycling facilities (range of 4-54 in other published studies). (Lusk et al., 2013, Am J of Public Health).
- In Montreal, a study of 6 cycle tracks showed an average cyclist injury rate 28% lower than on nearby “reference streets.” (Lusk et al, Injury Prevention, 2011).