Functional Harmony: The Restriction of Through Traffic in City Centers
Introduction: What is Systematic Safety?
The Systematic Safety law (proposed in 1992, and adopted in 1997), is the Dutch Road Safety Program, aiming to eliminate high risk and dangerous areas before collisions and injuries can occur. Systematic Safety is comprised of 5 principles, the second of which is Functional Harmony.
Functional Harmony in Delft
Functional Harmony is the principle of removing incompatible road functions from the streets, for example, removing cut through traffic from residential neighborhoods. To understand why cut through traffic streets and residential streets are deemed incompatible, the Dutch have defined four types of streets. Every street or road in the Netherlands is one of these four types:
- Local Road: residential neighborhoods and shopping streets. 20 mph target speed limit
- No lane markings – more priority to pedestrians and cyclists
- Traffic diversion
- On street parking
- Neighborhood Principals: target speed of 25 mph
- 1 travel lane per direction
- Possible Bike lanes
- Frequent Crosswalks with pedestrian islands
- Urban Arterials: target speed of 30 mph
- Signalized crossings
- Separated Bike Paths
- No high intensity commercial activity
- Regional Flow Roads
- Wide intersection spacing
- Limited access functions
- No storefronts or driveways
Many Dutch cities have historic city centers. The streets in Delft, for example, are predominantly local roads, as they predate the invention of cars and thus are narrower and can not hold traffic. This is important when attempting to remove incompatible road functions.
Typical Local Street in Delft Historic City Center
Other streets in Delft, like the one below, are wide enough for through traffic, which if used for car traffic can result in incompatible functions.
Functional Harmony in Dutch Practice: Delft
Faced with historically narrow streets (built prior to cars) and busy storefronts and residences from corner to corner, almost the entirety of the city center street grid fell into the Local Road designation under the Functional Harmony principle. The city now had to remove incompatible road functions from the city center. The incompatible road functions were local streets (with associated compatible functions: shopping, residential, safe biking and safe walking, efficient biking and efficient walking networks) being used by locals for local road functions and by through traffic.
Vehicles would cut through the tight network of local streets in the city center in order to reach destinations both in the center, and not in the center. This caused the entire city center to became a space for through traffic, even though it is the main shopping area for the city.
Delft decided that to preserve and improve the city center vibrancy, as well as character and culture of the city and central residential neighborhoods, the streets needed to be returned to the people. Delft set out to make the city center a combination of car-free and car-lite areas.
Car-Lite vs. Car-Free
Car-free areas are when cars, delivery trucks, and busses are not allowed onto streets in an area, and only walking and biking are permitted. No vehicular traffic is allowed. Car-lite areas are pedestrian and bicycling priority streets and areas where cars and vehicles are guests. In a commercial car-lite area, private vehicles are usually banned, and delivery trucks can drive in to make deliveries at certain times. In residential car-lite areas, residents can have a car, but the streets are designed so that only local residents will drive in that area. Car-Lite is more practical and logistically simpler for cities to manage. They keep out through traffic, and in some cases all traffic, while maintaining functionality for business deliveries and city service vehicles.
The Groningen Model:
The northern Dutch city of Groningen pioneered a street design model for dealing with the through traffic problems that Groningen and Delft both had in their city centers. The model is shown below in it’s simplest form:
The black circle is the ring road. This allows cars to get to the city center and access the neighborhoods from the exterior, but not allow into the city center neighborhoods. The city center within the ring road is divided up into compartments. These compartments have few entrances for cars, which are all located on the ring road. Cars can not drive from compartment to compartment without driving on the ring road; as illustrated by the dotted black arrows, the path of cars is to go in and back out onto the ring road. The separation between the compartments are barriers, indicated in red, and so it is literally impossible for through car traffic to go through these neighborhoods.
Barriers are defined broadly. They can be a bollard, a stretch of canal with no bridges, a stretch of buildings with no streets coming through, and many other variations. The Groningen model diagram shows these barriers as a line, but in reality they are a string of barriers that form a car-lite or pedestrian area. The function of barriers is to block car traffic so that through traffic is eliminated. The compartments are essentially large scale dead ends, where only residents in these areas would need to drive. There is no car connection to other parts of the city, so through traffic disappears in the neighborhoods because there is no where for cars to go.
It is important to recognize that barriers block car traffic, but not bicyclists or pedestrians. These barriers are actually permeable barriers: blocking cars and vehicles, but allowing bikes and pedestrians to permeate the barrier to access the car-lite and pedestrian areas beyond the barriers. In the Groningen model, car through traffic is eliminated within the core, but due to the nature of permeable barriers, through trips for pedestrians and bicyclists are still allowed. Their trips actually become safer as car traffic is reduced and/or eliminated, reducing conflicts on the street.
The Groningen Model: Delft Application
Delft’s city center has a similar set up to Groningen. There is a ring road around the historic city center, which has been used to divert through traffic out of the center, to around the center.
The ring road is indicated by the black line. The green and blue overlays are the separate neighborhood compartments. Most of the compartments have direct access via the ring road, however some of the inner compartments have bridge connections that lead directly to the ring roads. In the Groningen model, there is absolutely no car connections across barriers between compartments. In Delft, however, there are car connections between compartments. However, car traffic was still able to be eliminated because the street grid is irregular. This means that cars trying to cut through can not do it quickly since there are so many turns and intersections, in addition to new barriers installed. Most cars go in and out of their compartments via the ring road and rarely cross into other compartments via car.
The red lines above are the barriers to cars, with the red overlay indicating the area between the barriers that have been made car-lite and car-free. Many of the barriers in Delft are made by long stretches of canals and buildings without crossings or streets. This limits accessibility to areas by car, as many of these long stretches do in fact have some small cut throughs or bridges that can logistically only be navigated on foot or by bike.
Other barriers were put in intentionally to deter or restrict cars. For example, there are bollards and signs, which are very common. These barriers are permeable, where bikes and pedestrians can flow freely through the barriers, unlike hard barriers like canals and buildings which block all modes.
The most common form of permeable barriers in Delft are bollards:
Sometimes the road and the sidewalk are leveled out when approaching a permeable barrier, prompting cars to slow down as they turn away from the barrier. In the background of this picture below, the only indicator of a barrier is the “no entry sign”. This works as a barrier to cars because drivers don’t want to go the wrong way down a road, or in a place they don’t belong because it’s illegal, and they can get in trouble with law enforcement.
The surface material of the streets also serve to deter cut through traffic. The ring road around the city center is paved with asphalt, which is ideal for cars as it allows for higher speeds and a smoother ride. This is in contrast to the streets of the city center, where they are paved with brick, which is less smooth of a ride for cars and does not allow for high speeds. As a driver, the asphalt is more appealing and most cars will thus stick to the ring road to drive around the city center.
Application in the United States: North End
The North End of Boston, Massachusetts, is similar to Delft in that they are both historical areas with an unorganized street grid, and are popular shopping centers and residential areas. The North End is where Delft was 20 years ago: narrow, local streets built before cars overrun by vehicular through traffic.
The North End is in a position to go car-lite. The North End has it’s own ring road, just like Delft. The historic street grid within the ring road is irregular with almost no straight roads crossing the area, just like Delft.
Based on the research and design of Delft and Groningen, I am proposing that Hanover street becomes car-lite. The ring road around the edge will stay open to cars and the existing bus route, so that cars can get to the North End and park on the edges in garages (currently in existence), but not so cars can go into the North End. I’m proposing splitting the North End into 4 compartments with a central car-lite zone. This car-lite zone is made in between the permeable car barriers (as in Delft) separating the compartments, and also happens to be the busiest commercial zone of the North End.
The North End redesign will look more like the original Groningen model than Delft, as no cars can go in between the compartments and must use the ring road to go to another compartment. In addition to the barriers separating compartments, there are also barriers within compartments. This is to reduce the number of entrances and exits into compartments from the ring road. Additionally, barriers are installed halfway down some blocks in order to reduce the number of car circulation routes within compartments. The idea is that only local traffic would want to or need to drive into these compartments.