Thread by @FWBRyeg

Another, recent research paper we hope urban infrastructure planners have read:
nature.com/articles/s4159…

Researchers Szell et al synthesized an urban bike network development model, then tested it against reality of 62 cities. Their findings point to the need for city authorities to recognize the need to get to a critical threshold, quickly. /2

IOWs "cities must invest into bicycle networks with the right growth strategy, and persistently, to surpass a critical mass."
(Remember the time @CityofEdmonton built a #bikelane, then removed it? Apparently a classic cold feet/shying at an initial decreasing return error). /3

Szell & colleagues were motivated by the overwhelming scientific consensus that meeting the 1.5° goal is required to resolve the #ClimateCrisis; that #transport is the most problematic sector & with most humans living in cities, making #urbantransport sustainable is urgent. /4

They note that while EVs are "a potential solution to exhaust pollution", they bring the same issues as combustion cars: space allocation, road safety, particulate matter pollution that is mainly caused by non-exhaust emissions, public health & equity. EVs are not the answer. /5

They say "boosting active travel in cities has some of the highest potential to mitigate #ClimateChange & to improve public health". They're also aware of "historical political inertia in growing 🚲 networks". Hence the research on city-wide, comprehensive dev't strategies. /6

What's really compelling about their modelling is how it confronts the received wisdom (from Amsterdam & Copenhagen, eg: the Dutch CROW manual most planners rely on) that it takes decades to develop a bike network that enough people will use. /7

They then model possible bike network growth strategies as if from scratch, based on their sample of 62 cities, using criteria of #betweenness, #closeness, & #random growth. (They use 'from scratch' b/c most cities have negligible 🚲 infra, w/ 100s of disconnected components.) /8

What their research shows is:
"To be successful in developing well-connected bicycle networks, cities must invest with the right growth strategy, & *persistently*, to surpass a *critical mass*."
*Persistence & *Critical Mass are 🗝️ points. /9

Is it time in the thread for an image?
Here's Szell et al's infographic showing the gradient between 'economic' (el cheapo/$0.00) & most resilient (🚲-preferred/fully connected) types of bike networks: nature.com/articles/s4159…
/10

Perhaps you want to see their modelling? Edmonton isn't in the list of 62 cities, but Montrèal & Toronto are:
growbike.net/city/montreal

growbike.net/city/toronto
/11

The biggest take-away, for Edmonton's situation is this: bike network consolidation (convergence of directness, connectedness & efficiency) happens at different stages, depending on the growth strategy adopted. /12

•Betweenness growth=fast coverage, intermediate connectedness & directness, & low local efficiency.
•Closeness growth=optimal connectedness & local efficiency but slow coverage.
•Random growth=fastest coverage but low directness, connectedness, & efficiency.
/13

In all strategies, there is a dip, & then transition. This is 🗝️ for policy & planning: the transition point represents ⬆️investment in network building. Stopping investment & growth b4 transition leads to a net loss in investment. Pushing past the threshold leads to big gains!

The common “random growth” strategy that follows local, stepwise refinement [ie: as a part of Neighbourhood Renewal...] substantially shifts the critical threshold, holds up the development of a functional cycling infrastructure & can fuel objections to bike lane expansions. /15

We've seen this in Edmonton, already: “We've already built many bike lanes but nobody is using them, so why build more?”
Szell et all emphasize: "it is not a network’s length that matters but how you grow it." /16

Comparing their modelling to actual cities found close parallels, & policy implications:
"To grow bicycle networks successfully, cities must invest into them persistently, to surpass short-term deficiencies until a critical mass of 🚲 infrastructure has been built up." /17 /end