Miami-Dade Safe Streets Alliance
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Making Miami-Dade Neighborhood Streets Safer By Discouraging & Slowing Cut-Thru Traffic
Nationally, neighborhood streets have some of the highest pedestrian and cyclist injury rates of all road types. Excessive cut-thru traffic is a key factor jeopardizing the safety of our neighborhood streets.
As main roads become more congested, cut-thru traffic increases. Fortunately, there are a number of measures for making neighborhood streets safer by reducing and slowing cut-thru traffic. The most important measure is to reduce the main road congestion that prompts drivers to cut-thru neighborhood streets to get around slow traffic. These measures include improved bus and other transit services, making it easier for commuters to use car-pools or work from home, as well as improved walking and cycling facilities.
Unfortunately, some Miami-Dade officials have opted for opening even more neighborhood streets to cut-thru traffic in an effort to reduce congestion. This approach will have minimal effect on congestion while making a few more neighborhood streets even more dangerous.
We believe this effort began because we Miami-Dade residents have not provided our elected officials with the public support they need to pursue more effective congestion-reduction measures as well as those that make neighborhood streets safer such as raised pedestrian crossings, bike lanes, and other traffic calming measures. So, please join with us in supporting our elected officials by signing the Miami-Dade Safe Streets Alliance petition.
What is the Miami-Dade Safe Streets Alliance?
In a 2014 report, the Miami-Dade County Metropolitan Planning Organization proposed opening 14 Miami-Dade County streets to cut-thru traffic by constructing bridges over canals or highways. The 14 bridge locations are shown and listed below.
The Alliance was founded by the residents of the neighborhoods threatened by the large increase in traffic due to the proposed bridges. The neighborhood residents learned that streets with excessive cut-thru traffic are among the most dangerous of all roads with regard to pedestrians, cyclists and others injured. This prompted the residents come together and form the Miami-Dade Safe Streets Alliance.
Proposed Palmetto Bay 77th & 87th Street Canal Bridges
The 2014 report proposed opening SW 77th & SW 87th Streets to cut-thru traffic by bridging canals at the three locations show in the following maps.Bridges & SW 77th Avenue Traffic
The map below is from a 2017 Village study. The deeper red the street color, the more traffic the street carries. Yellow to orange streets carry less traffic. Note that SW 77th Avenue is presently yellow and only carries 1,000 vehicles/day while Old Cutler Road is the deepest red and has a traffic volume of 19,000 to 23,000 vehicles/day. We believe that the two bridges would result in a large portion of Old Cutler Road traffic using SW 77th to bypass congestion.
As SW 77th Avenue becomes increasingly busy, traffic may disperse throughout the community making the connecting neighborhood streets less safe as well. As cut-thru traffic volume increases, so do vehicle caused injuries to pedestrians, cyclists, and others walking, playing, or biking along our neighborhood streets. In fact, traffic data analyses show neighborhood streets have some of the highest accident rates of all road types.
Bridge & SW 87th Avenue Traffic
The map below is from a 2017 Village study. The streets with the deeper red color carry the greatest traffic volume. Yellow to orange streets carry the least traffic. Note that between 160th and 168th, SW 87th Avenue is presently yellow and only carries 2,000 vehicles/day. SW 87th at 168th is the deepest red and has a traffic volume of 11,016 vehicles/day. We believe the bridge would result in a large portion of those 11,016 vehicles/day using SW 87th to bypass congestion.
As SW 87th Avenue becomes increasingly busy, traffic will likely disperse throughout the neighborhood making the connecting streets less safe as well. As cut-thru traffic volume increases, so do vehicle caused injuries to those walking, playing, or biking along our neighborhood streets. In fact, traffic data analyses show neighborhood streets have some of the highest accident rates of all road types.
Why the Bridges Will Only Bring Temporary Congestion Relief
For decades it was thought that the best way to solve congestion was to build more roads. While this may be true where very large capacity increases are achieved, this doesn’t work with the much smaller capacity increase achieved by bridging SW 77th Avenue. The reason is an effect transportation researchers call induced travel. Once road capacity is increased and congestion lessens, people who used to avoid driving are induced to do so again. After a period of months or several years, induced travel brings traffic volume and congestion back to where it was before. For this small respite from congestion, those who live on streets opened to cut-thru traffic will suffer a much longer period of more dangerous streets.Why does cut-thru traffic make neighborhood streets more dangerous?
Cut-thru traffic tends to operate at a higher speed, which increases the likelihood of accidents and the severity of injury for the reasons shown the following graphic:- a pedestrian is nearly twice as likely to die if struck by a car traveling at 30 mph compared to 20 mph,
- as speed increases a driver’s field of vision narrows, which makes it more likely that pedestrians and cyclists will not be seen until its too late to avoid an accident, and
- a car travelling at 30 mph requires twice the distance to fully stop compared to 20 mph.
Making Neighborhood Streets Safer Success Examples
Here are a few making neighborhood streets safer success examples:- Between 2013 and 2016, New York City reduced traffic-related fatalities by 23% while nationally they increased by 7%,
- Speed humps and other traffic calming measures have reduced crashes on neighborhood streets by up to 45%,
- Holding back left-turning traffic for 3-7 seconds at signalized intersections has reduced pedestrian injuries by 60%, and
- A sizable portion of cut-thru traffic can be attributed to apps that steer drivers from congested main roads onto neighborhood streets. Very frustrated officials in one town felt they had no choice but to close off neighborhood streets to rush hour cut-thru traffic.
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.”
To put these numbers in perspective, each single-family home generates one peak-hour trip and ten trips per day. These trips include the cars and SUVs driven by residents along with 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.
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 (late-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. Sadly, the alternate route is frequently a through-street bisecting a residential neighborhood. As shown in the figure below, traffic congestion is rated using a system known as Level of Service or LOS. The rating goes from A to F. The “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.
Traffic Calming Measures
The goal of these measures is first to slow traffic speed then reduce excessive traffic volume. Both actions make neighborhood streets safer for those crossing or walking-biking along the street and less hazardous for children playing nearby. The following table summarizes the effectiveness of three categories of approaches for making neighborhood streets safer.
Traffic calming is divided into three areas: education, enforcement and engineered measures. While all three are vital, only engineered measures provide lasting benefits. The following discussion is based mostly on the Center for Problem-Solving Policing webpage Responses to the Problem of Speeding in Residential Areas. Other traffic calming resources can be found at:
Education
These measures can range from a brochure to half-day programs given at local schools. Education must be the first step in any traffic calming effort. Before installing speed humps or other engineered measures on a neighborhood street it is essential that residents learn why they are needed. Residents must then have an opportunity to participate in decision-making about what approaches will be used. If done right most residents will support the effort.Enforcement
Police departments have found that enforcement can be effective if four criteria are met:- drivers believe they’ll be ticketed if they speed,
- it has meaningful costs to offenders,
- police apply it generally, rather than at specific times and locations, and
- drivers are not tipped off by cues as to when enforcement is or is not happening.
Speed cameras can be effective. Other measures, like the speed sign to the right, only reduce speed for a few weeks. Every neighborhood seems to have a couple of residents who insist upon driving ridiculously fast. Most police departments will visit these individuals at home if alerted by other residents. This can be effective. Arresting the most severe offenders is quite effective but may require legislation giving police the authority to take this action.
Engineered Measures
These traffic calming measures range from safer crosswalks to closing off a street to through traffic.
Speed Humps span both travel lanes and are typically two- or three-inches high. They reduce speed to 20 or 30 mph. They are easier to cross and more acceptable to emergency services than speed bumps.
Traffic Circles reduce mid-block speed by 10% and
intersection collisions by up to 70%. Roundabouts or rotaries are similar but are used where larger traffic volumes are anticipated and typically have two lanes of traffic in the circle. traffic circle
Chicanes are installed mid-block to narrow a street or to impart gentle curves, both of which cause drivers to slow-down. By narrowing the width of the street, chicanes also make it safer for pedestrians to cross.
Center Island Narrowing provides a safer 
crossing for pedestrians and can reduce speed. Some emergency service agency find this to be the most acceptable calming measure. center island
If cut-through traffic becomes excessive on a narrow, neighborhood street then one option is to close the street off at one end. Simply making a street one-way can reduce cut-through traffic by half.
Measures With Limited Effectiveness
The following measures have been found to have minimal impact upon speeding:- Reducing speed limits,
- Increasing fines and penalties,
- Stop signs, and
- Speed bumps (as opposed to humps) and rumble strips.
How to Ensure Measures Really Do Calm Cut-Thru Traffic
Many transportation agencies face a conflict when it comes to traffic calming measures. On the one hand, no one would argue that calming measures make neighborhood streets safer by discouraging cut-thru traffic. On the other hand, traffic agencies rely upon cut-thru traffic to reduce main road congestion. This conflict can result in the design of calming measures that serve more as a pacifier rather than achieving the goal of safer neighborhood streets. For example, one study showed a substantial difference in the effectiveness of speed humps with an entrance ramp slope of less than 5%. This same study documented that speed humps spaced 82 feet apart achieved a 25% lower speed compared to a spacing of 1300 feet. Combined, a slope of >5% and spacing of 82 feet slowed traffic by an average of 5 mph more compared to speed humps with <5% slope and 1300-foot spacing.
It is not uncommon that folks say that while their neighborhood streets have speed humps or other calming measures they do not seem to have much effect on cut-thru traffic volume or speed. We suspect the poor performance is mostly due to poor design. In other words, the measures may have been designed more as pacifiers than to achieve a significant improvement in neighborhood street safety.
The recommended spacing for speed humps is every 260- to 500-feet. A typical speed hump:
- Extends from edge of street pavement to edge of pavement,
- Has a length of 12 feet, which
- Means it must be at least 3.6-inches high to achieve a 5% entrance ramp slope.
Liability & Traffic Calming
Concerns about liability are occassionally voiced by cities, counties, or other jurisdictions considering the use of speed humps and other traffic calming measures. The following text from a U.S. Federal Highway Administration guidance document shows the liability concern is exagerated when it comes to traffic calming:“2.7 Legal Issues Liability
Few jurisdictions have been successfully sued over liability issues related to traffic calming measures. The successful lawsuits have generally been the result of improper or inadequate maintenance of signs or pavement markings, not because a traffic calming measure was determined to be inherently unsafe.
It is the duty of the public entity to make sure the roadway system is safe for the intended use of that roadway. In order to establish negligence on the part of a public entity, the injured party must establish (1) that the government agency owed a duty to that person, (2) that the duty was breached by an act or a failure to act, (3) that the breach of duty was the proximate cause of the injury or loss to the complainant, and (4) that the government had adequate notice of the dangerous condition.
In order to minimize the potential for any liability, a public agency should develop and maintain documentation of every step in the traffic calming program process.