Riding the City
Suburban Cul-de-Sacs Make Short Trips Long
A destination half a mile away as the crow flies can be a three-mile ride in a subdivision, and the cause is street connectivity rather than distance.
In many American suburbs the store is visible from the house and still takes fifteen minutes to reach by bike. The distance is short; the network connecting them is not.
Connectivity is a measurable property of a street network
Planners compare straight-line distance between two points with the distance actually travelable on the network. The ratio describes how directly the streets connect.
A dense grid produces a ratio close to one, because there is usually a street heading roughly the right way. A branching subdivision produces a much higher ratio.
That ratio is what a rider experiences as a detour, and it applies to every trip within the neighborhood rather than to one awkward corner.
The tree structure has one exit
Postwar subdivision layouts are typically hierarchical: cul-de-sacs feed loop streets, loop streets feed a collector, and the collector meets the arterial at one or two points.
Any trip leaving the neighborhood must therefore route through the collector, regardless of which direction the destination lies in.
The design was intended to keep through traffic off residential streets, and it succeeds at that. The cost is that local trips inherit the same constraint.
Detour length falls hardest on the slowest modes
An extra mile of driving is a minute or two and disappears into the trip. The same mile on foot is twenty minutes and on a bike is several.
Because walking and cycling are more sensitive to distance, network detours suppress them disproportionately even where the underlying separation is small.
This is one reason short trips in low-connectivity areas are made by car at very high rates. The car is absorbing a penalty the other modes cannot.
Cut-throughs change the map more than lanes do
A paved path linking the end of a cul-de-sac to the street behind it can remove a mile of detour at a fraction of the cost of any lane project.
These connections are attractive to planners for that reason, and many newer subdivision codes require them where a block exceeds a certain length.
They are also contested, since residents often bought into the layout specifically for its lack of through movement, which makes each one a local negotiation.
Retrofitting is easier at the edges than the middle
Existing neighborhoods rarely gain new streets, but they can gain connections along drainage corridors, utility easements, school grounds, and park boundaries.
These edges are often already public land, so a connection there needs less acquisition than one between two private lots.
Mapping where a short link would collapse a long detour is usually the highest-value analysis a suburban jurisdiction can run before it spends anything on pavement.
Questions readers ask
Why do people ride on the road next to a cycle path?
Usually because the path is slower, gives up priority at every side road, or does not go where they are going. Directness is a real requirement, not a preference.
Why does a new cycle route sometimes seem little used?
Often because it does not yet connect to anything at either end. Network value grows as links join up, so early sections can look disappointing until the gaps close.
