Neighborhoods - Street Networks

Street corridors are the connective tissue for cities. High value street corridors don’t just provide a pathway for cars and trucks, they can provide communities with places of commerce, human interaction, and even civic pride.  Street corridors are often a visitor’s first impression of a city – and they can’t be hidden from view.

A Community’s vibrancy is inextricably linked to the quality of its street corridors. Vibrant walkable cities have street corridors that encourage (not just allow) multiple forms of transportation such as: buses, streetcars, bicycles, scooters, and – the oldest and most reliable form of transportation: pedestrians (both abled and disabled). Street corridors that encourage a multi-modal set of transportation options increase the value of private property along them.  This is because those street corridors have multiple ways people can access the buildings and business along them, allow a greater number of slower moving people to occupy them, and offer environments which encourage visitors to stay longer and return sooner.

Even in neighborhoods where a lower level of vibrancy is desired, well-connected street networks – which are designed with the pedestrian in the forefront of the designer’s mind – provide a more valuable asset for a community. Reasonably narrow streets, with cars parked along both sides, with short block-lengths and many intersections, result in more walkable, livable neighborhoods.

If a community has too few streets, or too many streets that are disconnected, traffic on those few streets that actually do connect can become choked. Many American suburbs have subdivisions that access main arterial streets in only a few intersecting places.  In addition to insinuating an unhealthy isolated lifestyle for residents, disconnected street networks force every driver onto the same few arterial streets to start their morning commute or buy a loaf of bread.  This, along with segregated land uses, is the primary cause for traffic congestion – not a lack of vehicle lanes.

Contrary to an often held opinion, disconnected street networks are less safe. Traditional, pedestrian-friendly neighborhoods have a tightly woven network of intersecting streets.  In contrast, most conventional communities developed in America after World War II have roads that are too long (meaning with too few intersections); roads that are too wide; and roads that have very little “street friction” (on-street parking, streetlights, etc.). The result is a set of roads that encourage fast moving vehicles to the detriment of pedestrians, bicyclists, and even vehicle occupants. One analysis (Marshall & Garrick), which studied over 130,000 crashes, showed that vehicle occupants are twice as likely to die, or have severe injuries, in cities with fewer intersections (disconnected) than in cities with more intersections (well-connected).  One of America’s sad ironies is that many people purchase homes in cul-de-sac neighborhoods thinking they are safer; in reality they are not – “unless those people never leave their cul-de-sac” (Marshall, quoted in City Lab, September 9, 2011).

Disconnected street networks can also delay emergency responders. During a design charrette a police officer recounted an experience he had with cul-de-sac neighborhoods. He was parked in one cul-de-sac neighborhood when he was called to an emergency run for an adjacent cul-de-sac neighborhood.  He had to drive a circuitous route to get where he needed to go – even though he could see through back yards to the other emergency. The overuse of cul-de-sacs in suburban America has created an absurd environment.

Well connected street networks, on the other hand, are safer and healthier than disconnected ones. They usually result in slower vehicular traffic speeds (calmer traffic) because there are more connective intersections with stop signs and stoplights.  This is much safer for pedestrians, bicyclists, and even vehicle occupants. Where street corridors provide safer more comfortable places for pedestrians, people will populate those sidewalks along with the homes and business that line them. Well connected, traditionally developed, neighborhoods are economically healthy and sustainable for the long term.

Contrary to what many believe, well-connected street networks with reasonable narrow roads, also have a high transportation capacity. Through an engineering analysis Walter Kulash, one of the USA’s most preeminent traffic engineers, proved that fine-grained street networks not only provide better systems for pedestrians, bicyclists, and micro-mobile travelers, they actually have more capacity for motor vehicles than less connected road networks (often found in suburban environments). 

The street network of most existing cities, and even of most suburbs, is pretty well set.  However, changes are always occurring to street networks – they evolve incrementally over time.  Often communities seek to modify portions of their street networks to try to solve a perceived problem like traffic congestion (by widening a road) or through traffic (by cutting off a road).  Unfortunately, those modifications often create more problems than they solve.  

A robust, well-intersected street network will provide a community with a long-term infrastructure that can weather economic slow-downs, periodic ebbs in development activity, and other occasional threats to vitality, because they provide fertile ground for thriving urbane areas.  Well-connected street networks have been providing a sustainable structure for cities for decades – even centuries.