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A Transportation Vision For Boulder—Urban Design, Part 3


By

Editor’s note: Throughout the summer and fall we will run a serialized version of PLAN-Boulder County’s A Transportation Vision for Boulder. This is part 3 of section 2. To read the entire paper, start with the Introduction.


Safety

When a traffic engineer states the newly designed road will “improve” safety, it usually means fewer fender benders, but it generally also means more serious accidents and more accidents involving pedestrians. Conventional, car-oriented ways to make a street “safer” usually tend to increase motor vehicle speeds, which makes the streets less safe for pedestrians or bicyclists. Sixteen percent of all people killed in motor vehicle accidents are pedestrians and bicyclists—way out of proportion to the number of pedestrians and bicyclists on the streets. Thirty-nine percent of all children killed in motor vehicle accidents are killed while walking or riding a bicycle. When we hear traffic engineers tell us that the road improvement will improve safety, we need to ask them to precisely define what the safety problem and proposed improvements are.

Forgiving Streets vs. Attentive Streets

For more than 70 years, the guiding principle for improving road safety was to design the forgiving street. That is, design the road so that if a motorist drove too fast or too inattentively, she or he would be “forgiven.” Common ways to “forgive” such driving are to remove street trees because motorists might crash into them when leaving the roadway, widen the width of travel lanes to reduce the incidence of vehicles brushing each other, and pull buildings back from the corners of intersections to give motorists the ability to view further down the street to see if there is on-coming or cross traffic. Each of these tactics seems sensible because many car crashes involve motorists crashing into trees, brushing a vehicle in an adjoining lane, or not seeing an on-coming car.

But Hans Monderman, a Dutch traffic engineer, made a ground-breaking discovery: there is a terrible unintended consequence of forgiving streets—a consequence that erodes roadway safety. He pointed out what any behavioral scientist would realize: that forgiving streets are inducing motorists to drive too fast and too inattentively, thereby reducing safety. Why? Because motorists, by nature, tend to drive at the highest possible speed and attentiveness level that feels comfortably safe. This is why speed limit signs tend to be ineffective at slowing vehicles. Therefore, because forgiving streets make motorists feel safer, they drive faster and more inattentively on them.

Monderman showed that by designing roads for slower, more attentive speeds, road safety improved dramatically. Monderman further advocated not only retaining street trees and encouraging pedestrian or bicycle activity on and near the road, but also called for the removal of warning signs, warning lights, painted road markings, and other conventional safety features. Too much signage distracts drivers, according to Monderman. The absence of such “safety” features places drivers on their best behavior. By removing “safety” devices, motorists are obligated by the design of the road to drive more carefully. There is less speeding, and there is less texting or eating while driving.

Fire Safety vs. Life Safety

Similarly, Peter Swift conducted a study in Longmont, Colorado in the 1990s in which he found that if a community widened its roadways or increased the size or turning radii at its intersections to accommodate large fire trucks (to improve fire safety through the shortening of fire truck response times), the number of community injuries and deaths increased.

Why? Because while a few victims of fires were aided by shorter response times, the more ample roads and intersections were causing higher levels of injuries and deaths due to vehicle crashes that came from higher speed, less attentive motorists. In other words, the number of road injuries and deaths caused by the bigger roads and intersections far exceeded the number of averted injuries and deaths due to faster fire truck response times. The conclusion: Fire safety is only a subset of the larger picture of life safety. By looking at overall life safety, we avoid more community injuries and deaths by keeping roads and intersections smaller in size.

The safest streets in a community, counter-intuitively, tend to be give-way streets. These are two-way streets, usually with on-street parking, that are so narrow that motorists are compelled to drive slowly, attentively, and courteously. One motorist must give way when another motorist approaches from the opposite direction.

In sum, dramatic safety improvements come from street designs that:

  • Retain or restore modest street widths and dimensions
  • Minimize the use of road markings and other features that create a false sense of security
  • Move trees back to the edges of streets, and restore the small town ambiance tradition of moving buildings close to street intersections

Céret, France, main street 2

Céret, France. Place de la République and Rue du Maréchal Joffre, August 2006 (Image source: Wikimedia commons)


We must be vigilant in ensuring that road design modifications are comprehensive enough to include all road users, not just speeding, inattentive motorists. Streets—particularly in town centers—should be designed to induce slow and attentive speeds to improve safety for all road users.

One-Way Streets

Creating one-way streets was popular a number of decades ago as a low-cost way to quickly move high volumes of traffic through a town center. Perceived benefits included “improved” traffic flow, a low cost way to add motor vehicle capacity, and a way to reduce traffic conflicts.

However, there are a large number of problems with one-way streets that tend to overwhelm the suggested benefits. Nationally, cities are converting one-way streets back to two-way because of the many problems that one-ways create. For example, Ecologically Sustainable Design Pty Ltd (2005) reports that “[m]any of these town centres [in the United States] became quite degraded, unattractive and unsafe into the 1980s and 1990s, in part as a result of the impact of car-based sprawl development beyond the town centres, but also because of the effects of traffic dominance on the one-way streets.”[1]

One-way streets result in a significant increase in speeding. Former shopping streets that often included residences become increasingly abandoned drive-throughs instead of drive-tos. By increasing average motor vehicle speeds, one-way streets tend to induce lower-value car trips that were previously discouraged by slower-speed travel. This induced travel increases per capita motor vehicle travel, which increases air and noise pollution, and gas consumption.

Because one-way streets remove on-coming traffic, friction is reduced and the motorist therefore has less of an obligation to pay attention while driving. Without the risk of an on-coming car, the potential cost of straying from the travel lane is reduced, which leads some motorists to be less attentive and less vigilant.

Long-standing, one-way streets seem to lose residences and businesses due to the noisier, higher speed conditions.[2] For a residence, in addition to the perceived increase in danger and noise pollution, the higher speeds create the impression of excessive traffic volumes, even if volumes are modest. For businesses, harm may occur in multiple ways:

  • Reduced storefront exposure as one direction of travel is eliminated
  • Reduced storefront exposure as the speed of motor vehicles increases and motorists have less time to read a storefront or sign
  • Increased inconvenience for delivery trucks

The resulting loss in residential quality and commercial value causes a decline in property values.

Also on one-way streets, higher average motor vehicle speeds tend to make entering an existing the street more difficult and unsafe for a motorist, as reaction times or gaps in traffic flow tend to be smaller.

Backtracking or circuitous travel also increases with one-ways, as the most direct route to a destination is often made unavailable. This problem is particularly likely for newcomers to a community who are unfamiliar with the local road network. Frustration and getting lost are common experiences for visitors to a community characterized by a great many one-ways. Rick Hall of Hall Engineering indicates that one-way backtracking tends to more than counter-balance any expected time saving benefits that one-ways provide to motorists.[3] Backtracking is also made more likely because higher average motor vehicle speeds lead to an increase in the motorist not seeing her destination until she has passed it.

Because one-way streets often require indirect, out-of-the-way travel, some motorists or bicyclists will occasionally violate traffic laws by traveling the wrong way on a one-way street, particularly if the distance is short or the perception of being caught is low. In addition, a number of travelers will unintentionally travel in the wrong direction because they don’t realize the street is one-way. This is especially true for newcomers to a community, possibly resulting in unsafe driving.

One-way streets can result in a declining number of pedestrians, bicyclists and transit users. As the average speed of motor vehicles increases, the street becomes increasingly unsafe or is perceived as unsafe for non-motorists. Pedestrian and bicycle travel on such streets therefore declines as walkers or bicyclists either seek out more welcoming streets, or opt not to walk or bicycle at all. Non-motorists, in this case, are fleeing due to a phenomenon known as the barrier effect, where real or perceived barriers discourage or prevent use of a product or facility.

One-way streets tend to increase motorist frustration, in part because the reduced friction of the one-way creates the expectation that the street should now be entirely free of delays. Any slowing down or stopping obligated by traffic signals or vehicle turning movements is therefore more likely to induce dangerous “road rage” reactions and rudeness by motorists. In a powerful, high-speed motor vehicle, a driver becomes extremely dangerous to himself and others when induced to feel impatient, enraged, or rude. This is particularly unsafe for senior citizens and children.

Increased anxiety and danger are not only experienced by pedestrians and bicyclists, but also motorists. When other motorists are driving faster, more impatiently and inattentively, one feels rushed when driving a motor vehicle.

Tellingly, suburbs almost never have large, high-speed, one-way streets, as suburban residents are aware that such streets harm property values.

According to Ecologically Sustainable Design Pty Ltd (2005), “There is less evidence of North American towns undertaking rigorous … investigations into the potential benefits of undertaking conversions from one-way to two-way.  Rather, it has become widely accepted amongst urban regeneration practitioners that virtually all town centre conversions to two-way streets will be beneficial; it is now more a matter of identifying the range of complimentary improvements needed to catalyze the best returns from the conversion.”

John Gilderbloom reports many substantial benefits of converting one-way streets back to two-way operation. Among them are the large number of new pedestrians and bicyclists, a substantial reduction in crashes, a large increase in neighborhood livability and property values, a large reduction in crime, and a large increase in homeowner and business owner improvements to their properties.[4]

There is very little that is more important for town center street design than obligating slower-speed, attentive, patient, courteous driving by motorists. The lack of well-behaved driving is toxic to city health. If the objective is to improve safety, comfort, convenience, quality of life, economic health, and transportation choice, two-way street design is nearly always essential.

Suburban Sprawl

Low-density sprawl is an extremely important concern for PLAN-Boulder County because it reduces travel and lifestyle choice, it induces high levels of air emissions and energy consumption, and is a financial Ponzi scheme.[5]

Because of a travel time budget, known as Marchetti’s constant, most people have a set tolerance for total commute times. Increasing the speed of car travel induces more sprawling, dispersed, spread-out patterns of community development, as motorists return to their travel time budget by, in many instances, living further away from their daily destinations. [On average, the commuter round-trip budget is about 1.1 hours per day. See: http://en.wikipedia.org/wiki/Marchetti’s_constant[6] ].

Sprawl is also induced when a community devotes too much of its resources to making cars happy rather than humans. This involves building over-sized roads, intersections and parking lots in town, which creates a less hospitable habitat for humans, and causes some residents to relocate from in-town locations to more remote locations.

This flight from unpleasant car-oriented infrastructure has been much less prevalent in Boulder than other American communities because the very high quality of life here tends to exceed the detrimental impacts that over-providing for cars has on quality of life. Nevertheless, even in Boulder, a not insignificant number of people are happier living in outlying areas than within Boulder city limits due to the over-allocation of car infrastructure (often referred to as a “concrete jungle”) in Boulder. As an aside, much sprawl in the region occurs in the construction of residential subdivisions that have leapfrogged over Boulder’s greenbelt.

Effective tools for discouraging sprawl include:

  • Downsizing over-sized roads, intersections and parking, coupled with a moratorium on enlarging the size of such facilities
  • Optimizing roads and parking by pricing them
  • Returning to design and development of transportation systems that make people happy, not cars

Read the next installment: Regional Transportation and Sustainable Travel


[1] Cars tend to dominate on one-way streets because the lack of “slowing friction” on such streets encourages motorists to drive at excessive, inattentive speeds, which creates large barriers to travel on one-way streets by bicyclists in particular.

[2] While this is less true in Boulder due to the relatively high incomes found here, it is likely that even in town center Boulder, one-way streets would be more healthy and would draw more pedestrians as two-way streets.

[3] Personal communication, August 2008.

[4] See http://www.planetizen.com/node/69354

[5] http://www.strongtowns.org/the-growth-ponzi-scheme/

[6] See references for more citations regarding the travel time budget.


The mission of PLAN-Boulder County is to ensure environmental sustainability, promote far-sighted, innovative, and sustainable land use and growth patterns, preserve the area’s unique character and desirability, and reduce our carbon footprint and environmental impact.

PLAN-Boulder County envisions Boulder County as mostly rural with open land between cities and towns that support working farms on good agricultural land and provides for conservation of critical habitats for wildlife and native flora. Within Boulder and neighboring communities, urban boundaries limit sprawl and growth is directed to meet community goals of housing affordability, diversity of all kinds, environmental sustainability, neighborhood identity, and a high quality of life. PLAN-Boulder County further supports green building practices that minimize energy use and greenhouse gas emissions. In addition, PLAN-Boulder County supports a more balanced transportation system that actively promotes public transit, bicycle commuting, and pedestrian travel, and provides for smarter use of automobiles.

The opinions expressed in this paper are those of the authors and do not represent the views of the various city and county organizations with which the authors are affiliated.

Dom Nozzi, principal author of this paper, is a member of the PLAN-Boulder County Board of Directors and the City of Boulder Transportation Advisory Board. Mr. Nozzi has a BA in environmental science from SUNY Plattsburgh and a Master’s in town planning from Florida State Univ. For 20 years, he was a senior planner for Gainesville, Forida and was also a growth rate control planner for Boulder. He has authored several land development regulations for Gainesville, has given over 90 transportation speeches nationwide, and has had several transportation essays published in newspapers and magazines. His books include Road to Ruin and The Car is the Enemy of the City. He is a certified Complete Streets Instructor providing Complete Streets instruction throughout the nation.

Pat Shanks, Jeff McWhirter, Alan Boles and Scott McCarey also contributed to this paper.

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