A few weeks back Peter had an interesting post about retrofitting Albany. In his post he suggested that we know that certain neighbourhood street networks lead to better urban outcomes. They are more walkable and easier to serve by public transport, etc. – yet, we continue to churn out dysfunctional neighbourhoods.
Zooming in a bit lower from the neighbourhood structure, I thought it would be useful to consider what we know about residential streets. Here is a list of features of residential streets that are often considered desirable features:
- Narrow widths,
- Short blocks,
- Continuous street trees (between the footpath and kerb),
- On street parking that is often occupied,
- Lots of intersections, preferably X-type.
Lets take a closer look at narrow streets. While outdated road manuals tend to require wider lane dimensions, more sweeping curves, and clear sightlines, we know that that these designs increase vehicle speeds, increase stopping distances, and lead to more crashes as well as more severe crashes.
Narrow streets, in particular ones with parked cars and continuous street trees, slow vehicles. This is something that can be observed by using the street and experiencing how the geometry and complexities require much more attention which in turn slows drivers.
We know that narrow and slower streets lead to safer streets. A study surveying 6000 streets in Longmont, Colorado, (Residential Street Typology and Injury Accident Frequency) found:
“As street widths widen, accidents per mile per year increases exponentially, and the safest residential street width are the narrowest (curb face).”
Specifically they found that a typical 36-foot (11m) wide residential street has a 487 percent increase in accident rates compared to 24-foot (7.3) street.
Here is an 11 metre wide street in Favona (Mckinstry Ave). It is representative of a 1970s-era neighbourhood street in Auckland. This street type is common across Auckland and New Zealand.
And below is a 7.3m wide street in Balmoral/Mt Eden.
The following is a quick look at the accident data of those particular streets over the last 15 years from the NZTA CAS database. This is a screenshot of crash data in the Mt Eden neighbourhood north of Balmoral Road.
Looking at the residential streets (not Dominion or Sandringham Roads) there are very few (11) crashes and all are classed minor injury.
Here is the same scale screenshot of the Favona neighbourhood.
What stands out immediately is the sparse and branching street network. The difficulty in providing public transport and the requirement for car ownership and associated carparking space represents an unfunded liability both for the residents of this area and the rest of the city.
Another liability is the safety issue associated with these types of streets.
Not counting Buckland Road (it’s an arterial), the equivalent study area has about 12 minor injury crashes, but significantly one fatal crash on Mckinstry Ave.
This unscientific snapshot seems to be consistent with the Longmont research. At some point I’ll run a GIS analysis of the crash data to test international research.
Besides confirming what we know, it would be good to start developing solutions to make these wide and curvey streets safer, and of course to stop building them like this in the first place.
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The good thing is that both developers and AT are nowadays much keener/willing to use narrow streets on new projects (this from my own professional experience of working on several development projects). There’s been quite a change in the last 10 years.
The bad thing is that there’s still very little money or appetite yet to retrofit the thousand kilometres of racetracks we have built through our suburbs.
It does seem so in some cases – I have family moving to the new Long Bay developments (which I thoroughly oppose) and the kerbs seem built out with trees and obstacles to slow things down. Still nowhere to walk to though.
“Nowhere to walk to” seems a bit harsh – there’s the Long Bay beach itself, and the regional park, and the high school next door, the primary school slightly further away, and there will be some local shops in the future. Must be at least as good as most other suburbs from that perspective.
‘At least as good’ still isn’t good 🙂 It’s just another auto-dependant suburb pushing nature that much further away.
A few 30km/hr speed limit signs should do it, can’t cost much can it? Unlike most countries, most NZers abide by the speed limit (+ tolerance) as we have so many cops out there trying to make their quota. If AT drop the speed limit on residential streets, people will slow down. Why spend stupid amounts of money to redesign existing streets when a simple change in speed limit will probably do (at least try it). I notice they have done this in Hamilton.
Of course for new developments a grid of narrow streets seems to make sense (to slow people down, to save land, and to save costs)
You are joking right? For every 10km/h you drop a posted speed limit without doing anything else, at best you usually see a 2-3km/h reduction in mean speeds. If you’re just after *some* reduction in speeds, then that might be fine, but if you’re actually aiming to get 30km/h travel speeds you’ll need something more in terms of street environment.
FWIW I think 30Km/hour would be a negative move. This is not because I think 50Km/hour just fine. I don’t and on residential streets I try to keep it to 40. But I think that if you actually posted 30 a lot of people would just snort with disbelief and unless they thought there might be cops around, they would ignore it. I really do think that posting 40Km/hour would be an excellent move for residential streets, and would have considerable effect. I think 30 would be resented and ignored.
Could be wrong but …
jj
Make it harder to drive fast and keep cars out if they don’t need to be there: http://blog.davidroos.co.nz/content.html?id=20150412WestEnd
This matches my experience in Pukekohe. Our street -Victoria Street – has seen far fewer speeding vehicles (and therefore, one hopes, fewer accidents) since they put in chicanes a year or two ago.
jj
Chicanes are dreadful things. Just put in kerb build outs along the street. 6m wide max
Sorry, I am using the wrong language. I think chicanes are those things that you kind of do a slalom through? If so, then I am talking about kerb buildouts. They are just kind of U-shaped things that stick into the road. But they have definitely stopped the hooning up and down Victoria Street in Pukekohe.
jj
In that case then, yes, you are correct. Where I live: https://onedrive.live.com/redir?resid=F31283F46AE7B673!10858&authkey=!ANAW4-nwcPwNMPI&v=3&ithint=photo%2cjpg
Requires the trees though – they’ve done the build outs down a side street near us, but it has had no effect as the road still looks wide, so folk still drive fast. There does seem to be some slowdown when there’s a lot of cars parked between build outs, which suggests that trees in the build outs may work.
I read an article some years ago where an experimental street system was retro fitted to glen Innes. Trees were planted in the middle of the street and playspaces and other obstacles placed in or near the road. This is not disimilar to shared spaces which basically humanise the street. I tried to do the same thing by deliberately designing a narrow lane with twists and turns and poor sight lines to serve 7 new village style houses. Auckland Councils urban designer ” freaked” and couldnt be convinced, despite Europe being full of such lanes. Bureaucratic inertia is the prime reason that innovative living is not a reality in New Zealand
This is the (Point England) study I believe you mean – http://www.sciencedirect.com/science/article/pii/S0001457510001703. Treated local streets are still there (although a couple of the plants need a bit of TLC). I’m a big fan of vertical things in the middle of the road like that because they break up the sight-line down the road, and available sight distance is one of the key influences on people’s travel speeds.
I’ve driven through there quite a bit and I hate the trees in the middle of the road. I find them distracting and that distraction tends to keep your focus on the object in the middle of the road rather than the entire road and kerbs.
Some of the extra width can be used to create cycle lanes. They can be at the roadway level, or raised above (so the kerb would be between the cycle lane and the roadway). But, important, they should have some bright color, like green or pink. Having those bright colored lanes next to the roadway makes it appear more narrow.
I love it how some of these things are presented as fact when they are not.
Many readers may be interested to know that this is not international best practice and we should not be changing our streets to satisfy a small, angry mob of white people who have a bizarre hatred for cars. In saying that some aspects of this article hold true. Road width for instance can be a relevant factor in some instances.
Evidence shows that if we get rid of traffic obstructions, street signs and other impediments that are passed off in NZ as “traffic calming” it results in better outcomes for all. Cars move more efficiently and with lower congestion the road becomes a safer place for other users.
https://www.minds.com/blog/view/248215469679448064/german-town-abolishes-traffic-lights-and-codes-accidents-are-now-almost-non-existent
http://thecityfix.com/blog/naked-streets-without-traffic-lights-improve-flow-and-safety/
We need to base our roading on common sense and courtesy, not rules and restrictions.
Are you serious Matthew? Faster moving cars is safer for little kids crossing the road?! There is no reason for cars to be doing more than 30kmph on a residential street.
Those links you give actually refer to removing of signs and controls of vehicles and giving priority to pedestrians. They already had narrow streets to begin with and high pedestrian numbers to bring speeds down. You cant apply that in NZ because cars have right of way on the roads which is half the problem.
That’s what the evidence shows
If we clear cars more efficiently through the streets it creates greater periods in which other users can utilise the street
What twaddle. ‘Clear cars more efficiently’ is mumbo-jumbo for give cars all the space and allow them to go faster. This always results in higher death and injury for every other user, until and unless all other users are banished from the route, ie is it a motorway?
I’ve been in Germany most of last month, German people are very friendly, German drivers not so friendly, you may be correct about the over us of signs doesn’t help.
Once of the motor-way the speed limits are low, nearly all residential streets are 30kmh with lots of street calming and narrowed. There are also lots speed cameras. I don’t agree with you reference is evidence from what I’ve seen.
But German drivers are friendlier than the Parisians whose road have very few making.
“a small, angry mob of white people who have a bizarre hatred for cars” – Unlike the small angry mob of white men who have a bizarre love of cars and basically designed the auto dependent Auckland that we are all now trying to change?
I know the examples of Bohmte and Poynton well as I wrote this blog post for CAA: http://caa.org.nz/the-benefits-of-traffic-anarchy/
You are completely missing the point of what was done in those towns. The point was to create uncertainty for motorists so they would be more careful and give pedestrians and cyclists a chance to actually use the roads. Not to increase the traffic flow or reduce congestion.
And it worked as it brought the high street back to life.
So they basically created shared spaces. Not the pseudo motorways that you and your (presumably non-white) ilk would turn every residential street into.
So it’s white people this week. Last week he was making offensive comments about Polynesians.
With his latest idiotic “logic” motorways would be the safest streets for pedestrians!
Hmm I wouldn’t describe it as an angry mob. Hipsters maybe, but not a mob.
But you are most definitely right about the need for common sense and courtesy.
The issue at hand is that currently the only thing taken into consideration is making it as convenient as possible for cars to pass through. Without any regard for other people. The first step is recognizing that walking (or cycling) somewhere instead of driving is a legit use of the road.
Drive through any street, with shops on both sides, and you’ll see pedestrians standing on the center line, waiting to cross the other half of the street. With cars passing by centimeters away on both sides. I don’t consider that a normal situation, in my opinion there should be a safer (saner?) way to get to the other side of the street. Like a zebra crossing or a traffic light. Does that qualify as a bizarre hatred for cars? I don’t think so, I would call that basic courtesy towards people living on those streets.
Now courtesy is something that goes both ways of course. Putting random obstacles on the street to slow cars down is just obnoxious and dangerous. Maybe it’s OK on the really quiet residential streets, but I can’t see that working out well on main streets or arterials.
“there should be a safer (saner?) way to get to the other side of the street. Like a zebra crossing or a traffic light”
or slow the traffic to such an extent that it’s easy to find a gap to cross the road, cars have time to stop if you make a mistake and it’s unlikely your killed if they can’t stop.
Good point. If someone actually has the stones to lower the speed limit.
But then again… see http://m.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11442350
I think even places like Hustmere Road in Takapuna (the part between Anzac Ave and Lake Rd) still have a limit of 50kph.
“Cars move more efficiently…” You say that like it’s a good thing. Greater efficiency for people who choose to walk, cycle, or use public transport, and less for people who choose cars. That’s the answer.
The best outcome is greater efficiency for all road users.
Road efficiency for cars and other road users is not necessarily a mutually exclusive concept as the case studies show.
You forget that we are talking about places people live. Efficiency of movement may be the primary focus for arterials, but for residential streets their primary focus is as a place.
I’m intrigued how many people misinterpret the “naked streets” stuff. What you see clearly in Drachten and other places that have implemented this type of approach is that SPEED MANAGEMENT via street design is the key. You can take out all the signs, signals and markings you like if you start with a layout of narrow streets, with textured surfacings, raised platforms, etc that reduce maximum travel speeds. So traffic calming (or “impediments”) are an essential part of making them work. You couldn’t just do this with typical NZ streets and expect a miracle tomorrow.
I’m not so sure about the desirability of “occupied on-street parking”. To me this clutters a neighbourhood with ugliness. It also adds a big hazard for cyclists unless the street is a purely local one with only low-speed traffic and no driver-expectation of any ‘main-thoroughfare’ status.
One of the major hazards that urban cyclists face is the conflicting need to, 1) give parked cars a wide-enough berth to be safe from suddenly-opening doors, and 2) ride as close to the left as possible so as not to be in the way of moving traffic. Unfortunately It takes a very wide road to provide enough room for this conflict not to occur:
a) 0.2m distance of parked vehicle out from kerb,
b) 1.8m width of parked cars
c) 1m door-zone clearance for cyclists
d) 0.5m handlebar-width of bicycle itself
e) 1.5m recommended bicycle-clearance allowance for overtaking traffic
f) 2.5m width of traffic itself (allowing for larger vehicles)
g) 0.5m clearence of traffic from the centre-line.
That all tots up to 8m per-direction, or *16m kerb-kerb road-width*!
Without parked cars, b) and c) can be eliminated, thus reducing the conflict-free-road-width to 5.2m each side, or 10.4m kerb-kerb.
Methods of preventing this from becoming a race-track are either:
i) to provide kerbed bays for the parked traffic such that even when vacant the parking does not look like part of the road, or
ii) to provide dedicated bike lanes out-of-the-way of the door-zone, and reduce the width available for moving-traffic.
Roads of less-than this width, which are intended as, or at least used as traffic-thoroughfares and make no specific provision for bicycles, should not allow on-street parking.
I’d be interested in seeing what an urban street would look like under your proposal. I tend to favor residential street designs that slow vehicles to a point where bicycles can easily use every street. I recognize that there are few places in NZ where this is possible due to the road rules, intersection designs, neighbourhood structure, and street design.
We’re really talking about two different scenarios here:
(1) Arterial routes where parking is an optional extra so, sure, remove parking if need be so that you can provide suitable safe/efficient provision for cycling and motor vehicles respectively.
(2) Local streets where access, not efficient thoroughfare, is the key, and the speed/volume profile should be low enough for bikes to easily take the lane. On-street parking can help to achieve sped reduction.
I had a student recently look at the effect of parking levels on local street speeds. Between on-street parking levels of 0% to 100%, there was about a 10km/h difference from one extreme to the other. See here for the IPENZ-TG Conf paper – http://conf.hardingconsultants.co.nz/workspace/uploads/paper-koorey-glen-effect-55060e66a3367.pdf
Thanks for sharing. This is interesting.
I do wonder how the correlation is with traffic density. I don’t see any data on number of cars passing through the different streets. If there is a higher number of cars going through the wider roads, then there is a higher chance of having more incidents anyway, due to the density of the traffic. More cars, more accidents. Fewer cars, fewer accidents. Does that sound logic?
Sounds logic. The study mentions they only consider streets with “less than 2,500 Average Daily Traffic (ADT)”.
If there’s correlation between traffic volume and street width, then this will skew the outcome of this study. But I suspect street width is not dependent on the traffic volume, but rather on the guidelines of the period when any area was developed.
I was thinking the same thing; exposure to traffic volumes is generally the biggest predictor of crash numbers (not necessarily linear though). In comparing Mt Eden with Favona for example, you have neglected to mention that none of the local Mt Eden streets have more than 2000veh/day, whereas McKinstry Ave has ~6000veh/day. That’s why all crash models I know of start with traffic flow (e.g. AADT) being a default factor and then look to add other possible modifying factors such as road width, traffic speed, intersection type, or whatever else you’re investigating.
Hence I was somewhat sceptical of the relationship derived in Longmont with the y-axis showing “accidents per mile per year”. If it was “accidents per veh-miles travelled” then it might be more meaningful. I suspect that traffic volumes are reasonably well correlated to road widths (i.e. busier roads usually have wider widths), so what you’re seeing in the chart, at least partly, is actually that busier roads have more accidents. Unfortunately the underlying paper doesn’t discuss collinearity between the factors studied; however it also notes that AADT was equally significant a predictive factor. Not an issue to have factors that are correlated, but potentially misleading to include only one in your model and imply that it is the causative factor.
I certainly believe that road width has an influence on traffic speeds and hence street safety, but we need to be careful not to overstate its value.
McKinstry has 6k VPD? Looking at a map of the area, this doesn’t make sense.
From what I recall the Longmont study was re-visited to include traffic volumes. And isn’t traffic volume a fundamental feature of the network design? In Mt Eden type grids you have 3-4 times more streets compare to the branching arterial-collector-local typology. This may be more relevant to analysing crash data across the neighbourhood street structure like Garrick has done?
Yeah, their second relationship showing accidents/yr/1000AADT is more useful (although their assessment of the AADT factor using a 5th order polynomial is not that helpful) – that accounts for traffic while still showing the effect of width.
As for road networks, certainly an unconstrained grid network will spread the traffic out more than a hierarchical “tributary” network (where you have limited choice about which route to take). That probably explains somewhat why McKinstry has so much traffic; it’s one of the few useful short-cuts here. However, the density of intersections is also a key determinant of traffic safety, particularly X-roads that traffic can drive straight through. I note that Mt Eden has a typical grid layout that includes a reasonable number of X-intersections, whereas Favona only has T-intersections. In both cases you’ll see that quite a lot of the crashes are located at intersections. On low-volume roads however it can be a bit of a crap-shoot as to where the next crash will occur; hence it’s better to look at aggregate numbers over an area and treat on an area-wide basis (e.g. low speed zone) rather than try to “fix” a local street crash site that probably won’t see another crash there for years/decades anyway.
This design concept implicitly directs traffic to adjoining arterial streets. In the two snapshots provided the number of accidents is higher in Mt Eden than in Favona when the arterial streets are included. If having less overall accidents is the preferred result, the wider curved street design appears to be better.
Safer residential streets is a lot broader than just considering traffic accident data. The impact of street design on other factors such as crime also needs to be considered. As an example there is evidence that burglaries are a lot lower for houses located on a street with only one exit than an area where multiple getaway routes are available to the offenders. The traffic design needs to be considered as part of the overall neighbourhood design and not in isolation.
Not sure where you’re getting your ‘evidence’ Martin; do let us know. I’m aware of plenty that says the opposite, in widely published studies. Space Syntax looked at various countries:
Britain: http://www.spacesyntax.net/symposia-archive/SSS2/SpSx%202nd%20Symposium%2099%20-2003%20pdf/2nd%20Symposium%20Vol%201%20pdf/29%20Shu%20300.pdf
Holland: http://joss.bartlett.ucl.ac.uk/journal/index.php/joss/article/viewFile/296/pdf_25
Taiwan: http://www.spacesyntax.net/symposia-archive/SSS4/fullpapers/46Shu-Huangpaper.pdf
Martin, I agree it would be good to consider some of the other impacts of street design. Here I’m focusing on crash data. Some of the other things worth considering might be: mode share, how kids get to school, social connections, obesity levels, maintenance cost, etc.
In case people haven’t clicked through, I’d urge you to have a look at the examples that David J Roos gives of streets in Vancouver – in his comment 3rd from the top. Some really good precedent examples of what looks like beautiful streets with built in traffic calming, and very clever cycle / pedestrian links, transforming standard grid traffic intersections into far more ped friendly crosswalks. Fantastic work David – some great examples for NZ to follow suit on.