Making Howard County MD Neighborhood Streets Safer

Why Cut-Thru Traffic Is A Problem

How Much Traffic Is Too Much for a Neighborhood Street

At What Point Does Main Road Congestion Cause Excessive Cut Thru Traffic

Reducing Cut-Thru Traffic

Cul-De-Sacs & Quality of Life

Preventing Cul-De-Sac Extensions

Why Excessive Cut-Thru Traffic Reflects Flawed Growth Management

Winning Responsible Growth & Traffic Management

Vision Zero

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Neighborhood Streets & Cut-Thru Traffic

If you're concerned about cut-thru traffic anywhere in the USA, contact CEDS at 410-654-3021 or Help@ceds.org to discuss strategy options.

Of all our roads, neighborhood streets have the highest accident rate.  And these accidents involve a substantially higher percentage of pedestrians and cyclists when compared to those occurring on other roads. 

through street

As main roads (blue arterials and gold collectors above) become increasingly congested, drivers seek out ways for getting around traffic jams.  Unfortunately, the alternative usually involves a neighborhood through-street like those in red and gold above.  This cut-thru traffic makes neighborhood streets noisier and more dangerous. 

dead end culdesacResearch shows that cut-thru traffic operates at a higher speed, which increases the likelihood of accidents and the severity of injury.  A pedestrian is six times more likely to die if struck by a car traveling at 30 mph compared to 20 mph.  Of even greater concern are situations where traffic volume increases because a court or other cul-de-sac (dead-end) street is turned into a through-street. 

Congested roads and rising neighborhood cut-thru traffic are a result of poorly managed growth.  In this webpage we'll explain how to resolve both in ways that can make neighborhood streets safer while accommodating a reasonable amount of growth.  Contact CEDS at 410-654-3021 or Help@ceds.org if you have any questions or would like our assistance making your street safer. 

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Why Cut-Thru Traffic Is A Problem

As traffic volume increases on a neighborhood street so does vehicle speed, accident frequency, noise, and even crime.  All of these impacts then decrease property value.

Table 1, below, shows that local roads/streets in urban areas have the highest crash (accident) rate.  In an urban setting, most of these local roads would be residential or neighborhood streets. 

crash rate by road type

This table is from Comprehensive Engineering Approach to Achieving Safe Neighborhoods

Table 1, shows that neighborhood streets are our most dangerous.  Research has determined that those using neighborhood streets to avoid main road congestion tend to drive at a higher speed.  The combined effect of cut-thru traffic increased speed and volume makes a neighborhood street even more dangerous.

It is generally true that as traffic volume increases, the value of homes along a street declines.  This is especially true for those living on courts and other cul-de-sac streets where homes can sell for up to 20% more than those located on through streets.

Converting cul-de-sacs to through streets interferes with the close neighbor relations that adds so much to quality of life.  For example, one sociologist found that:

bulb culdesac"people who live in traditional bulb cul-de-sacs have the highest levels of attitudinal and behavioral cohesion (covering both how they feel about their neighbors and how much they actually interact with them). People who live on your average residential through-street have the lowest levels..."

For parents living on courts or other low-volume streets, a rise in traffic volume may increase anxiety about allowing children - particularly younger kids - to play outside.  Children between the ages of 5 and 9 are particularly at risk to traffic-caused injury.  Converting cul-de-sacs to through-streets robs both children and their parents of a sense of safety and freedom many cherish.

With regard to crime, one study noted that:

"Furthermore, hierarchical, discontinuous street systems have lower burglary rates than easily traveled street layouts; criminals will avoid street patterns where they might get trapped. For example, the troubled Five Oaks district of Dayton, Ohio, was restructured to create several small neighborhoods by converting many local streets to cul-de-sacs by means of barriers. Within a short time traffic declined 67 percent and traffic accidents fell 40 percent. Overall crime decreased 26 percent, and violent crime fell by half. At the same time, home sales and values increased."

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How Much Traffic Is Too Much for a Neighborhood Street

While every through-street will carry traffic from one main road to another, neighborhood quality of life suffers when the volume crosses a certain threshold. 

Where is that threshold? 

The table below is from a paper that appeared in the Institute for Transportation Engineers Journal.  The term "environment" in the table is defined as:

"one where residents can live, work and move about in freedom from the hazards of motor traffic."

Environment Vehicles Per Minute Vehicles Per Day
Excellent 0.5 300
Good 0.5-1.0 300-600
Acceptable 1.0-2.0 600-1200
Poor >2.0 >1200

To put these numbers in perspective, each single-family detached home generates one peak-hour trip and ten trips per day.  This includes not just the cars and SUVs driven by residents but delivery trucks and all other traffic entering-exiting a neighborhood.  One would anticipate that those who live on a residential street prefer that traffic volume remain in the good to excellent range or less than 600 vehicles per day.  In other words, land use decisions should not cause traffic volume to exceed 600 vehicles per day on a neighborhood street.

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At What Point Does Main Road Congestion Cause Excessive Cut Thru Traffic

Commuters begin seeking alternate routes when congestion cuts main road (arterial-collector) speed to half the free-flow (mid-morning) speed.  For example, if free-flow speed is 40 mph then drivers begin seeking out alternates when congestion causes average speed to drop to 20 mph.  Of course the alternate route is frequently a through-street passing through a residential neighborhood.

As shown in the figure below, traffic congestion is rated using a system known as Level of Service ranging from A to F.  That "half-free-flow-speed" where drivers begin seeking alternate routes in earnest lies between a Level of Service of C to D.  So, to keep cut-thru traffic at a reasonable volume main road traffic congestion should not reach Level of Service D-E or F.

level of service

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Reducing Existing Cut-Thru Traffic

If traffic on your street exceeds the good to excellent range (300-600 vpd) given above, then consider calling for one or more of the many measures listed proven to reduce both cut-thru speed and volume.  The permanent measures given below are more effective and long-lasting.  For further detail click on the green measure name below.  For assistance in forming a traffic management strategy for your street(s) contact CEDS at 410-654-3021 or Help@ceds.org.

Measure Volume
Reduction
Speed
Reduction
Crash Reduction
Permanent:      
Full street closure 44%    
Half closure 42% 19%  
Diagonal diverters 35% 4%  
Speed hump 18-22% 22-23% 13-40%
Speed table 12% 18% 45%
Roadway narrowing 10% 4%  
Chokers 20% 14%  
Traffic circles 5% 11% 28%
Temporary:      
Speed trailers 9% 7% 10%
Speed limit signs 4% 7% 3%
Increased enforcement 8% 28% 28%

The data presented in this table is from Comprehensive Engineering Approach to Achieving Safe Neighborhoods

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Cul-De-Sacs & Quality of Life

Following is a summary of research demonstrating why cul-de-sacs and other dead-end neighborhood streets should not be converted into through-roads.

In a paper entitled The Cul-de-sac Effect: Relationship between Street Design and Residential Social Cohesion, published in the Journal of Urban Planning and Development, Volume 141 Issue 1 - March 2015, sociologist Thomas R. Hochschild Jr., reported:  “This study utilized a quasi-experimental design to assess differences in residential social cohesion for residents of “bulb” cul-de-sacs, “dead-end” cul-de-sacs, and through streets. My data reveal that bulb residents experience the highest levels of attitudinal and behavioral cohesion, followed by dead-ends, then through streets.”

5 Benefits of Cul-De-Sacs: “Promotes friendships and neighborly interaction: This hanging out potential also applies to whole families: parents, kids and other relatives and friends. As the cul-de-sac emphasizes the closeness of the houses within and the visibility of homes and families. In this way, the families are naturally encouraged to connect as well. Smiling and waving, checking in, connecting and even joining in games, parties and other social events naturally rise up in this design.”

Reconsidering the Cul-De-Sac: “Residents also preferred the cul-de-sac as a place to live, even if they actually lived on a through or loop street. People said they felt cul-de-sac streets were safer and quieter because there was no through traffic and what traffic there was moved slowly. They also felt they were more likely to know their neighbors. One resident’s comment was typical: “Our pets and kids are safer when there is a no-outlet street; you feel kidnapping is less likely—there is more of a sense of neighborhood.” Thus, the study generally corroborated earlier transportation research on the values of a hierarchical discontinuous street pattern. It also supported claims that cul-de-sacs are more frequently and more safely used by children.

The Benefits of Living in A Cul-De-Sac: “Because cul-de-sacs tend to have fewer homes than traditional streets, it is easier for people to get to know their neighbors in the cul-de-sac. Cul-de-sacs also are a natural place for neighbors to plan block parties or picnics because with proper permits from the local authorities, a cul-de-sac can be blocked off to any incoming or outgoing traffic during the block party. Homes in a cul-de-sac generally face outward toward the other homes, creating a greater sense of community for the residents as they can see their neighbors’ front doors from their own.”

Residential Street Design and Play: A literature review of policy, guidance and research on residential street design and its influence on children’s independent outdoor activity:  “Both traffic speed and volume have been found to have an effect on how streets are used. Appleyard’s study of three similar streets in San Francisco showed that residents’ quality of life was measurably affected by the volume of traffic in the street (Appleyard, 1981). Those living on a light-trafficked street knew more of their neighbors, felt a greater sense of belonging and were more familiar with its physical features. The study was replicated on residential streets in Bristol in 2011 and the findings resonated strongly with Appleyard’s (Hart & Parkhurst, 2011).”

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Preventing Cul-De-Sac Extensions

If you're concerned about a proposal to turn your cul-de-sac into a through-street then contact CEDS at 410-654-3021 or Help@ceds.org to discuss strategy options. 

road types

bulb culdesacTake a look at the streets highlighted black, above.  About a fourth to a third of the streets are courts or other cul-de-sacs.  The same is probably true for most of the U.S. 

Those who live on these cul-de-sacs paid up to 20% more for the increased safety and tranquility of these low-volume streets.  It is understandable then that cul-de-sac residents become irate when a proposal is made to open their street to cut-thru traffic.  It's even more infuriating when this is done to allow an adjacent property to be developed. 

Usually the justification for the extension is to provide a second means of emergency vehicle access should the main entrance ever be blocked by a downed tree, floodwaters, vehicle accident, etc.  Another justification is to increase road connectivity to relieve congestion on main routes.  The relief is achieved, of course, by increasing neighborhood street cut-thru traffic.

As stated above, increasing neighborhood cut-thru traffic to relieve congestion is a symptom of poor growth management.  While a second means of emergency access is certainly a legitimate need, there are ways of accommodating this need without forcing residents to sacrifice the safety and tranquility of their neighborhoods.

Before a cul-de-sac conversion is considered, all other options must be exhausted. 

CEDS has helped a number of communities with this issue.  We can frequently find an alternate, second access such as creating a new road off an existing collector or arterial that prevents neighborhood impact. 

If an alternate access is not available then other options must be considered.  If cul-de-sac extension is the only means for creating a second access and the second access is genuinely needed for public safety, then consideration should be given to gating the access so it  can only be opened by fire, ambulance, police and other emergency services personnel. 

 emergency access gate

To see an example of how CEDS can help you protect your cul-de-sac from being turned into a through-street click on: Preventing Cul-De-Sacs From Becoming Through Roads.

If for some reason an emergency-access-only gate is not an option, then a number of measures should be considered that reduce cut-thru traffic speed, volume and crash rates, like the speed humps referenced in the table above.  Public officials may argue that these measures interfere with snow-plowing and emergency vehicle travel time.  Rarely though do the benefits of the measures come up in these arguments.

As stated at the beginning of this webpage, neighborhood streets have the highest accident rate of all road types.  Homes located on cul-de-sacs are valued for up to 20% more, which generates higher property-tax revenue.  It's simply wrong to ask people to sacrifice the safety and tranquility of their neighborhood without exhausting all other options.  I suspect that if elected officials were aware of the higher accident rates, lower tax revenue, and injustice then more responsible policies would be adopted with regard to the conversion of cul-de-sacs into through streets. 

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Why Excessive Cut-Thru Traffic Reflects Flawed Growth Management

Responsible growth management seeks to prevent congestion from reaching the threshold (Level of Service D-E or F) where cut-thru traffic harms neighborhood quality of life. 

Ironically, increasing main road congestion seems to create pressure on public officials to engage in two practices that exacerbate neighborhood cut-thru traffic:

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Winning Responsible Growth & Traffic Management

So how would responsible growth management prevent main road congestion from reaching the point where rush-hour cut-thru traffic becomes excessive?  More importantly, how can you provide elected officials with the public support they need to manage growth responsibly?

Responsible growth management begins with a plan that identifies existing and future congestion problems then recommends solutions.  Next elected officials must allocate the funds required to make the infrastructure improvements many solutions require.  Finally, Concurrency and Adequate Public Facilities Ordinance (APFO) laws must be in place to prevent additional growth from being approved before solutions are fully implemented. 

CEDS has found that far too many growth management plans fail to show both existing and future congestion.  Without this information plan readers are left in the dark as to whether growth will make their streets safer or more dangerous.  To see what a good plan should provide see the Traffic Congestion section of the CEDS Comprehensive Plans, Master Plans & Quality of Life Growth Management webpage.

Infrastructure improvements frequently come years after congestion has become excessive.  Instead, the infrastructure projects must be included in capital improvement plan then fully funded, preferably through the use of impact fees.

Far too many APFO-Concurrency laws are so poorly written or enforced as to be ineffective.  This leaves local residents wondering if congestion is inevitable.  Of course it isn't.  A common flaw is that the congestion cut-off is set well beyond the point where cut-thru traffic becomes serious. 

Earlier this point was given as when average speed is cut in half and Level of Service drops below C-D.  Urban-suburban growth restrictions should kick in and postpone development which would add traffic to roads that will be at or below Level of Service D-E.  Instead the cut-off is frequently set at the point where average speed is reduced by 75% and congestion reaches Level of Service E-F.

Winning responsible traffic and growth management begins with homeowner and other neighborhood associations taking the following actions:

Vision Zero

The Vision Zero website describes this concept as...

"...a strategy to eliminate all traffic fatalities and severe injuries, while increasing safe, healthy, equitable mobility for all. First implemented in Sweden in the 1990s, Vision Zero has proved successful across Europe — and now it’s gaining momentum in major American cities."

Vision Zero seeks to achieve this goal by...

Consider urging your local elected officials to adopt a Vision Zero plan for your village, borough, town, city or county.  For further detail visit the Vision Zero resources page at: https://visionzeronetwork.org/resources/

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