Tag Archives: slow streets

Redeveloping the Boulder Community Hospital Site in Boulder, Colorado

By Dom Nozzi

January 27, 2017

The most important task of the urbanist is controlling size. – David Mohney

As owners of the Boulder Community Hospital (BCH) site bounded by Broadway, Alpine, 9th Street, and Balsam, the City of Boulder has a golden opportunity to demonstrate the preferred vision for creating compact, walkable development in appropriate locations within Boulder.

For too long, citizens have rightly attacked many new projects in Boulder. We now have a chance to show how to do it right.

The following is one man’s opinion about how we can do it right at the BCH site.

First Determine the Context

Our very first task in establishing a “How to Do It Right” vision is to determine the “context” of the site. Where is it located in the community? Is it a walkable town center? A drivable suburb? A farmable rural area? Only when we answer that question are we able to know which design tactics are appropriate and which are inappropriate. For example, if we are in a suburban context, it is inappropriate to insert shops and offices within the neighborhood, or use small building setbacks. However, if we are in a town center context, those design tactics are entirely appropriate and desirable.

transect

In the case of the BCH site, it is generally agreed by the City that the context is walkable town center (what is called “Urban Center Zone” in the above figure). It is now important, given that, to ensure that the design of the site is compatible with that vision.

How do we do that?

A Form-Based Code

Perhaps the most effective way to do that is to establish what is called a “form-based code (FBC)” or a “subcommunity overlay plan,” which was successfully used to guide the development of the Holiday neighborhood in North Boulder.

The FBC or plan emphasizes the importance of “form” by specifying the appropriate and desirable building placements, street dimensions, and building materials. This differs from the conventional “use-based” zoning codes, which over-emphasize the importance of uses within a building, and only specify designs and dimensions that are prohibited, rather than specifying what is desired by the community.

As Andres Duany notes[1]

…A FBC protects us from the tendency of modern designers to disregard timeless design principles in favor of “anything goes.” An “anything goes” ideology too often leads to “kitschy” buildings, unwalkable streets, and other aspects of low-quality urban design.

…A FBC protects us from the whims of boards and committees.

…A FBC is necessary so that the “various professions that affect urbanism will act with unity of purpose.” Without integrated codes, architects, civil engineers and landscape architects can undermine each others’ intentions by suboptimizing.

…A FBC is necessary because without it, buildings and streets are “shaped not by urban designers but by fire marshals, civil engineers, poverty advocates, market experts, accessibility standards, materials suppliers and liability attorneys” – none of whom tend to know or care about urban design.

…A FBC is necessary because “unguided neighborhood design tends, not to vitality, but to socioeconomic monocultures.” The wealthy, the middle-class, and the poor segregate from each other, as do shops and restaurants, offices, and manufacturing. A FBC can ensure a level of diversity without which walkability wilts.

…A FBC is necessary to reign in the tendency of contemporary architects to design “look at me” buildings that disrupt the urban fabric.

…A FBC is necessary to ensure that locally appropriate, traditional design is employed, rather than “Anywhere USA” design.

…A FBC is needed to protect against the tendency to suburbanize places that are intended to provide compact, walkable urbanism.

…A FBC is necessary to protect against the tendency to over-use greenery in inappropriate places such as walkable town centers. In particular, grass areas tend to be inappropriate in walkable centers. Over-using greenery is a common mistake that tends to undermine walkability.

…A FBC is needed because codes “can compensate for deficient professional training. Because schools continue to educate architects towards self-expression rather than towards context, to individual building rather than to the whole.”

We can craft a FBC in hands-on workshops driven by citizens and urban designers. When crafting a FBC, such workshops are called “charrettes,” where professional urban designers provide attendees with a one- or multi-day training course in the time-tested design principles of creating a successful town center, suburb, or rural area. Armed with such knowledge, citizens and designers craft a FBC that is appropriate for the context and community values.

Designing the BCH Site

The following are my own individual suggestions for a FBC that would employ time-tested principles for creating a successful walkable, lovable, charming town center.

The overall layout is compact and walkable. For example, building setbacks are human-scaled and quite modest. Private front and backyards are similarly small in size. Public parks are smaller pocket parks rather than larger, suburban, fields of grass (note that abundant grass and athletic fields are provided adjacent to the west of the BCH site). Some of these parks are relatively small public squares formed by buildings that face the square on all four sides. If surface parking is unavoidable at the site (and I would very strongly urge against such parking), the parking should be designed as a public square that occasionally accommodates parked cars. Block sizes are relatively small, based on a street grid, and include many intersections. Internal streets and alleys are plentiful and narrow enough to obligate slower speed, more attentive driving. Give-way streets, slow streets, woonerfs, and walking streets are all appropriate and desirable.

Internal streets should have a spacing of at least one-to-one (or two-to-one or one-to-two) ratio of flanking building height to street width. (Pearl Street Mall has a ratio that fall within the ranges below).

ratio

To promote vibrancy and safety, the City should encourage 24/7 activity by discouraging weekday businesses, such as offices, that close after 5. Businesses that close after 5 create night-time dead zones.

Service vehicles that may use streets, such as buses, delivery vehicles, or fire trucks should be small enough that they do not obligate the establishment of overly large streets or intersections. When such vehicles cannot be relatively small, it is appropriate for such vehicles to be obligated to move more slowly and carefully. Dimensions, in other words, should be human-scaled, not tractor-trailer-scaled.

If feasible, Goose Creek under the BCH site should be daylighted. It would be appropriate to create a bustling, miniature version of the San Antonio Riverwalk, with homes and shops lining the creek. At a minimum, a daylighted creek needs to be relatively permeable with several pedestrian crossings along the way to promote walkability. Since the BCH site is in a compact, walkable zone, wide suburban greenspaces flanking the creek would not be appropriate.

Alignments are more formal and rectilinear. Internal streets, sidewalks and alleys have a straight rather than curvilinear (suburban) trajectory. Street trees along a block face are of the same species (or at least have similar size and shape), have a large enough canopy to shade streets, and should be formally aligned in picturesque straight lines rather than suburban clumps. Building placement is square to streets and squares rather than rotated (to avoid “train wreck” alignment more appropriate for suburbs). Buildings that are rotated rather than parallel to streets and squares are unable to form comfortable spaces.

Streets deploy square curbs and gutters. Stormwater requirements should be relaxed at the site to prevent unwalkable oversizing of facilities. Streets are flanked by sidewalks. Signs used by businesses are kept relatively small in size. For human scale, visual appeal, and protection from weather, shops along the street are encouraged to use canopies, colonnades, arcades, and balconies. When feasible, civic buildings or other structures with strong verticality are used to terminate street vistas.

Turn lanes and slip lanes in streets are not allowed on the site.

Street lights are relatively short in height to create a romantic pedestrian ambiance and signal to motorists that they are in a slow-speed environment. They are full cut-off to avoid light pollution.

Buildings are clad in context-appropriate brick, stone, and wood. Matching the timeless traditional styles of the nearby Mapleton Hill neighborhood is desirable. Building height limit regulations exempt pitched roofs above the top floor of buildings to encourage pitched roof form and discourage the blocky nature of flat roofs. Obelisks and clock towers are also exempt from height limits.

Buildings taller than five stories should be discouraged for a number of reasons. First, they tend to be overwhelming to pedestrian/human scale. Second, they tend to induce excessive amounts of car parking. Finally, if we assume that the demand for floor space is finite at the BCH site, it is much preferable from the standpoint of walkability for there to be, say, 10 buildings that are 5 stories in height rather than 5 buildings that are 10 stories in height.

Floor-area-ratio (FAR) is a measure of how much square footage can be built on a given piece of land. A relatively high FAR is supportive of walking, transit, and bicycling. In commercial areas, FAR should be at least 1.0.[2]  Richard Untermann, a well-known urban designer, calls for FARs of 2.0-3.0 in town centers.[3]

FAR

Buildings along the street are often graced with front porches to promote sociability, citizen surveillance, and visual desirability.

Relatively small offices and retail shops are sensitively interspersed within the neighborhood. For additional walkable access to shops and services, Broadway to the west of the BCH site should incorporate designs which make the crossing more safe and permeable. Narrowing crossing distances and various slow-speed treatments can effectively achieve increased permeability.

First floors of buildings along sidewalks provide ample windows. First floors of buildings are not appropriate places for the parking of cars.

Given the affordable housing crisis in Boulder, ample affordable housing must be provided. Residences above shops are desirable, as are accessory dwelling units and co-ops. An important element in providing affordable housing will be the fact that the inclusion of shops, services and offices within the neighborhood, residences will be able to allocate larger proportions of household money to their homes and less to car ownership and maintenance (since the household would be able to shed cars by owning, say, one car instead of two, or two instead of three).

An important way to make housing more affordable is to unbundle the price of parking for residences from the price of housing. Available parking is modest in quantity and hidden away from the street. Parking is space efficient because shared parking is emphasized and tends to be either on-street or within stacked parking garages. No parking is allowed to abut streets, unless the parking is on-street, or in a stacked garage wrapped with retail and services along the street.

The BCH site is exempted from required parking, and is also exempt from landscaping requirements.

Unbundling the price of parking and reducing the land devoted to parking are both important ways to create more affordable housing.

The Washington Village neighborhood project a few blocks to the north on Broadway and Cedar is a good model for appropriately compact and walkable spacing at the BCH site.

Let’s not squander this important opportunity. Let’s insist that we build a neighborhood that fits the pattern of walkable Siena, Italy, not drivable Phoenix Arizona.

phoenix

 

References

[1] “Why We Code,” Sky Studio. http://www.studiosky.co/blog/why-we-code.html?utm_content=bufferdde8c&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer

[2] SNO-TRAN. Creating Transportation Choices Through Zoning: A Guide for Snohomish County Communities. Washington State (October 1994)

[3] Untermann, Richard. (1984). Accomodating the Pedestrian, pg190.

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What Are the Obstacles to Making Our Streets Safer?

By Dom Nozzi

July 1, 2016

There have been a great many traffic injuries and deaths in the Boulder area in recent weeks. This is a terrible tragedy and tracks what is happening nationally. If we are to call ourselves a civilized society, there are effective things we must do to make our streets safer.

A very large percentage of neighborhood streets in Boulder (and the region) are excessively wide, which induces excessive driving speeds and dangerously inattentive driving. Boulder needs to redesign many of these streets to be safer. Good tactics are the common and effective traffic calming measures which narrow the street (yet still allow adequate emergency vehicle response times), including the use of slow streets, give-way streets, design-for-slow-streetsand shared streets. Each of those designs deliver slow design speeds which are crucial for neighborhood safety. A quick, easy and low-cost way to create slower, more attentive neighborhood streets is to allow and encourage a lot more on-street car parking, in addition to bulb-outs, traffic circles and chicanes. Slow speed neighborhood streets dramatically improve neighborhood quality of life and safety, and effectively promote more walking, bicycling and sociable neighborhood interactions.

An extremely common suggestion to address dangerous speeding is to lower speed limits. But mounting signs with lower speed limits, as nearly all traffic engineers know, is highly ineffective unless we also redesign the street. The typical motor vehicle speeds are generated by the design speed of the street rather than speed limit signs (which are so commonly disregarded that many derisively call them “suggested” speed limits). It is also unfair to the motorist to install a speed limit sign that is far below the street design speed. When the street design strongly encourages motorists to drive at higher speeds than the speed limit, a large number of speeding violations and tickets result.

I have been a bicycle commuter in a great many cities in the US, and in my opinion, the state highways in Boulder (in particular, Broadway, Canyon, and 28th St) are among the most hostile, deadly state roads I have ever bicycled or walked. The state highways in Boulder are death traps not only for bicyclists, pedestrians, and transit users, but also motorists. Those streets (and their huge intersections) are too big and therefore too high speed to be located within a city. It is important to note that city health is promoted with slow speeds, so these state highways are undermining the quality of life in Boulder.

The fierce opposition to the Folsom street reconfiguration project, as well as opposition to other safety and quality of life street redesign measures such as the traffic calming program in the 1990s, suggests that many in the Boulder population are not ready to accept enactment of street designs which effectively improve street safety and quality of life.

Even in Boulder, it is nearly impossible for the vast majority to travel anywhere without a car. American cities (including Boulder) are designed so that regular, safe, convenient travel by bicycle, walking, or transit is out of the question for almost all of us (mostly because roads are too big and distances are too large). That means, inevitably, that large numbers of people are obligated to drive a car even though it is too dangerous for them to do so. They have had too much to drink. Or they are angry or emotionally upset. They are distracted or exhausted by their multi-tasking, busy lives. Or their driving skills are questionable due to age or poor eyesight or other factors. In a society where nearly all trips must be made by motor vehicle, this problem is large and unavoidable.

It is incumbent on us, therefore, to design our streets and communities to be more compact and slower in speed. Otherwise, dangerous streets and unacceptably high numbers road crashes will always be a part of our lives.

 

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The Junior Academy (Trailhead) Residential Project at 2600-block of 4th Street in Boulder, Colorado

By Dom Nozzi

April 25, 2015

A new neighborhood has been proposed on the west side of Boulder, Colorado. It is the former site of the Junior Academy, and is called “Trailhead” (due to its proximity to the popular Sanitas trail in western Boulder.

The proposed project is located adjacent to a walkable, compact, pre-1930s historic Mapleton Hill neighborhood within walking distance of the Boulder town center. The Mapleton neighborhood Bldr Aug 2015 (4)intent of my recommendations for the project is to see that the design of the project promotes walkability, sociability, neighborhood safety and security, travel choice (particularly for seniors and children), relatively low noise levels, timeless styles and design, and low per capita car trip generation.

Parking

Providing two-car garages for each unit is radically out of character within the Mapleton Hill neighborhood, undercuts pedestrian ambience by creating more sterile facades that send the message that the area is suburban drivable, rather than walkable. If any is provided, the project must unbundle the cost of the parking provided for each residential unit so that owners/renters have the option of paying less for the residence in exchange for having less parking provided to the unit. Ideally, no parking should be provided off-street for any of the residential units. On-street metered parking is highly preferable. Should this project provide any publicly-accessible parking, such parking must be modest in number and priced or metered.

Street Design

In the vicinity of this project, 4th Street must be traffic calmed. On-street parking – perhaps pocketed on-street parking formed with bulb-outs to reduce curb-to-curb width – should be at least one component of the traffic calming. Calming tactics should be focused on horizontal interventions (such as very narrow shared or slow or give-way streets, and perhaps using roundabouts or bulb-outs) rather than vertical strategies such as speed humps. Sidewalk on 4th Street must be provided along the length of this project. Any street lighting provided for/by the project on 4th Street must be pedestrian-scaled (i.e., no more than 15 feet in height) and full cut-off.

Density

This project should achieve the maximum allowable density and floor area ratio allowed by the land development code. If allowed by code, this project should incorporate accessory dwelling units. Front porches should be aligned and either abut the front ROW/sidewalk or be no more than a “conversational distance” from the sidewalk (i.e., front porches no more than 10 feet from the back of ROW/sidewalk).

Mixed Use

If allowed by code, this project should incorporate small scale retail and office components.

Re-Zoning (amendments to the land development code)

If not allowed by the land development code, the project property (and the Mapleton Hill neighborhood) should have its land development codes revised to allow higher densities, accessory dwelling units, more than one-family allowed per property, mixed use (to allow small-scale retail and office), smaller (or no) yard setbacks, a prohibition on (incompatible) modernist architectural styles, and elimination of any minimum parking requirements (maximum parking requirements should replace any minimum requirements).

In general, each of the above design recommendations will ensure compatibility with the Mapleton Hill neighborhood and would minimize per household car trips in the long run.

 

 

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The Proposed Student Village in Gainesville Florida

By Dom Nozzi

December 14, 2005

I reviewed plans for the design of a new “student village” in southwest Gainesville Florida in late 2005.

I am an enthusiastic advocate of walkable, quality urbanism and was therefore quite pleased to see the dense, mixed-use, walkable, compact design that had been created by a student studio project group for this southwest Gainesville location at the southwest gateway to the University of Florida campus.

Here are some items that concern me:

I believe it is unwise to allow the size of fire trucks to dictate the height of the buildings and the width of the travel lanes, as this plan proposes. If walkable design requires certain dimensions, I don’t think it is a good idea to revise those dimensions to accommodate over-sized trucks. I would suggest that the final report recommend that the City and County invest in smaller fire trucks (and maybe smaller transit vehicles) to accommodate the walkable, compact, human-scaled neighborhoods that we will increasingly be building in our communities.

Yes, buying such trucks would probably be more expensive. But it is a lot more expensive to save money on the conventional over-sized fire trucks and then be obligated to bear the large costs (car crashes, lower-value/lower-quality development, etc.) that result from those big trucks.

Quality urbanism is somewhat more expensive than mediocre urbanism, but this community needs to have the wisdom and the pride to willingly want to pay those extra costs by, for example, buying smaller fire trucks.

I was impressed by how the proposal is illustrating block size comparisons for the downtowns of well-known cities in other parts of the world. It is crucial for walkability that the block sizes used in the Student Village be as small as possible (200 to 400 ft). Note that Portland OR is widely admired for its modest block sizes.

Similarly, it is crucial that the design maximize connectivity and accessibility, as this significantly adds to travel choice and walkability, not to mention substantially reducing traffic congestion.

In my opinion, the design options are showing an over-abundance of park space. While I acknowledge that a large number of SMALL parks, plazas and squares is important for quality urbanism, we should be careful about relatively large parks. Such parks can detract from the human-scaled proximity that walkability requires by introducing walking Tetro_Student_Village_Renderings_003distances that are too large. As a side note, I would be concerned that the quantity of greenspace in the proposal might have a significant deadening effect on the Village — walkability is better promoted when we have a bustling, compact concentration of mixed and vibrant buildings in close proximity to each other. Parks, if not laid out modestly, can detract from that.

I wonder about how much dense urbanism we can realistically expect in this location. While it is close to the UF campus, I don’t know that it will contain a major transportation “crossroads” that throughout history has been essential in the emergence of dense urbanism. Main Street and University Avenue originally did that in Gainesville. Today, it is primarily the I-75 interchanges that provide such a critical mass of vehicle trips. Can we realistically expect a critical mass of trips in this location to drive dense urbanism? I believe this is an important question, as doing such things as changing land use designations from low density to high density doesn’t do much at all to influence the emergence of dense urbanism.

I am uncomfortable with the recommendation to allow buildings that are 7-10 stories high. Taller buildings typically detract from walkability, because they generally result in excessive amounts of auto parking surrounding them. Taller buildings also result in a smaller number of buildings in the Village. For walkability, I’d rather have, say, 6 five-story buildings than 3 ten-story buildings. More buildings means more vibrancy and more proximity, and less dead space. Paris, for example, is one of the great cities of the world with regard to quality urbanism, and I believe they limit their buildings to 5 stories.

I am uncomfortable with the idea of creating tall, dense development in the southwest corner of our urban area. Frankly, I don’t believe that poly-centric cities are a good idea. My concern is that a second “downtown” for Gainesville would drain retail, office and residential energy that is so desperately needed in Gainesville’s original downtown. Also, it seems to me that for the sake of creating a sense of community and reducing vehicle travel, our civic, socially-condensing institutions should be located in a single place (downtown, and to a lesser extent UF), rather than creating a second set of civic buildings at our urban edge.

One could argue, I suppose, that the Village could become a stand-alone “new city” that is distinct from Gainesville, but again, due to the lack of an important crossroads here, I’m not sure this is a realistic idea.

I applaud the project for recognizing the importance of creating low-design-speed streets in the Village. That is essential if this is to be a successful, dense, vibrant, walkable project. As I indicated at the meeting, there are a great many designs that can be introduced to slow vehicle speeds beyond creation of 10-foot wide travel lanes. I firmly believe that to create safer, low-speed, high-quality streets, we need to move back to the timeless tradition of re-introducing friction in our streets (on-street parking, buildings and street trees close to the street, bulb-outs, no more than 3 lanes of street width, etc.). Streets are safer when motorists are obligated to pay attention and be careful. Streets are less safe when we follow the “forgiving street” convention of removing friction, which enables inattentive, high-speed car travel.

A dilemma for this project in its desire to create low design speeds is that the Village is located in a suburban, high-speed environment. That means that when driving in this portion of our urban area, motorists have a very strong expectation of being able to drive very fast and very inattentively. That means that it is crucial that the Village incorporate strong, unmistakable messages at its borders. That is, high-visibility Gateway Street treatments are important. As a motorist enters the Village, the street should clearly announce that the motorist is entering a slow-speed, pedestrian-oriented village. Features that could be used to announce such a message might include a narrowing of the street, buildings closer to the street, lower-profile post-mounted traffic signals, perhaps a roundabout, landscaped monument signs (and maybe a banner of some sort) proudly announcing entrance to the village, on-street parking, brick paving, painted paving, etc.

In my opinion, parking strategies are essential to the success of this project as a walkable, vibrant, urban place. First, it is very important that this project strongly encourages (or if feasible, requires) new residential (and ideally, commercial) development to UNBUNDLE parking from the cost of the residential unit. The convention of bundling the cost of the parking into the price of the residence is almost begging people to own and use cars at the residence. Since the project recommends a strong transit element, I am confident that a good number of residents would opt to forego paying more for their residence by not purchasing a parking space (only possible if the parking is unbundled from the residential price).

I have some concerns about the project calling for structured, multi-story parking garages. The per-space cost for such parking is quite enormous, and I am not at all sure that the land/market where the Village is located will be able to justify such an expense. How many retailers or prospective residential tenants, in other words, would be willing to pay roughly $10,000 per parking space in this location? Also, I have learned over the years that people tend not to want to park in structured parking unless they will be parked for several hours (for a job, a major entertainment event, etc.). Typically, people don’t like parking in a garage in order to go shopping.

In sum, I believe that parking in the Village should emphasize priced parking — particularly on-street parking. Certainly, structured parking is preferable to surface parking because it minimizes the parking footprint, thereby promoting compact walkability and additional retail opportunities. But while I favor structured parking, I don’t know that we can expect the market to be able to provide it in the Village. This is not to say we should just have a free-for-all on surface parking. Surface parking can and needs to be controlled by having the Village be parking exempt (don’t require new development to provide parking). Downtown Gainesville, for example, is parking exempt — a necessity for any place that intends to be walkable. It also needs to be controlled by only allowing it to occur at the rear or side of buildings. Structured parking, by the way, should only be allowed if it is wrapped by office/retail/residential.

I would refer the designers of this proposal to Donald Shoup’s new book (The High Cost of Free Parking). In my 19 years as a city planner, it is one of the most magnificent book I have ever read. The book should be required reading for all planners, engineers and elected officials.

I have not seen this yet in the Village plan, but I assume that the plan will recommend that there is a modest build-to requirement that obligates buildings to be pulled up to the street and sidewalk.

In sum, I am quite impressed by the project, despite my concerns.

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Curbing the Expectation of Driving at High Speeds

By Dom Nozzi

Many of us who seek to make our world more conducive to happy people rather than happy cars are adamant about the importance of slowing car speeds in communities.

Residential streets typically do not promote the problem of high-speed, free-flowing traffic, but sometimes they do act in such a way when they are used for “cut-through” trips or if they are relatively large neighborhood streets which “collect” traffic fed from smaller streets in the neighborhood (usually called “collector” streets).

Lowering the average motorist speed is one of the most essential ways I can think of to improve quality of life. And the most effective way to do that is through calming strategies which design the street to force slow car travel. It is critical that we LOWER THE EXPECTATION of motorists to be driving at high speeds. High speed car travel in a community should not be considered the “default” way for a motorist to travel.

Tragically, conventional traffic engineers have designed our streets for the past 100 years to promote high-speed travel – even on what should be quiet, low-speed streets. The result is that too many motorists now believe that relatively high-speed driving is the norm.

If we instead start designing our communities so that, eventually, most streets in a community are designed for slow car travel, general expectations will evolve so that a motorist realizes that the normal manner of driving is to drive slow (except on interstate highways, of course). With such an expectation, there will be significantly less road rage (and related hostile driving) in calmed areas, because the motorist EXPECTS to drive slow.

Designing streets for slow speeds is particularly important on residential streets, because such streets are the places where we most expect children and seniors to be, and where people are in homes and bothered by the noise of high-speed car travel. We also need to slow cars on the BIG roads in our community to ensure we solidify a general motorist expectation that they are driving in a slow speed community.

“Road rage” and fast driving are NOT genetically programmed into humans. A slow-speed community is NOT unrealistic.

In a discussion about slower car speeds, it is important to note that speed limit signs have little or no impact on how fast a motorist drives. Average driving speed on a street is dictated by the “design speed” of the street. The conventional traffic engineering philosophy is to assume that safety is best achieved by designing the “forgiving” street. That is, to design the street so that the motorist is “forgiven” if they, say, drive too fast and lose control of their car.

What this means is that the street is made wide and obstructions are kept away from the shoulders so that a fast, out-of-control motorist will not smash into anything.

Unfortunately, this fails to take into account the motorist psychology. If you design a street for safe driving at 40 mph, the average motorist will drive 40 mph, even if the posted speed limit signs say 30 mph, because average driving speed is determined by the maximum speed a motorist feels comfortable driving.

Typically, this philosophy means that a street with a speed limit of 30 mph has been designed with a “design speed” of 40 mph. We should not be surprised when a large number of motorists drive 40 mph on such streets. Enforcement is nearly impossible, short of a police state.

Therefore, in my opinion, the “forgiving street” philosophy gives us LESS safety due to higher speed (and more inattentive) driving.

The effective solution for slowing cars is to “retrofit” our streets (including residential streets) with calming designs that force cars to slow down (which is why things like speed humps are often called “sleeping policemen”).

However, “vertical” treatments like humps are almost never, if ever, appropriate for streets (including residential streets) – particularly those that are on designated emergency vehicle routes (where calming needs to be carefully designed to not excessively impede such vehicles).

In the case of such routes, “horizontal” calming is usually called for. Horizontal treatments include such things as curb extensions or other forms of street narrowing, as opposed to “vertical” calming like humps.

Does Traffic Calming Increase Air Pollution?

A common objection to traffic calming is that air emissions will increase due to “stop and go” traffic that is induced by calming. But this concern makes the mistake of  being overly reductionist. Peter Newman and Jeffrey Kenworthy effectively point out why reductionism in this case leads to erroneous conclusions. Newman and Kenworthy correctly point out that those who fear higher emissions due to calming forget about changes in motorist behavior that occur with calming. Reductionist thinking in this case only looks at what is coming out of a tailpipe of individual cars.

But Newman and Kenworthy, take a broader and more accurate view by pointing out that changes in travel behavior (caused by higher development densities, shorter travel distances, congestion, calming, etc.) completely swamp any air pollution gains that can be realized from individual cars that have less stop-and-go travel.

I will grant that it is possible there will be “micro-level” increases in air pollution levels due to calming. But at the “macro” (community) level, I’m convinced there is a net reduction in air pollution. That is, there is LESS air pollution at the community level.

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