“Speed Sensitive Traffic Signals” use speed detectors (radar, road-loop etc.) in conjunction with a traffic signal to cause light to change to red if speeding is detected. For more information see Speed Sensitive Signals

Positive Results

• Significant evidence that speeding is controlled
• No negative impact of capacity reduction associated with Road Diets
• If desired, can be incorporated together with speed camera, to automatically issue speeding or red-light citations for drivers that cross red-light
• Works at all times of day and night, and does not rely on congestion required by Road Diets to control speed

Negative Results

• No evidence of negative results in studies over 10 years, used extensively in Europe, also USA.

Implementations

Successful working case in UK

“Beacon Controlled Crosswalks” use of flashing beacons at crosswalks, triggered by a pedestrian pressing button, to alert traffic that someone is crossing.

Positive Results

• A more visual indicator that a crossing is in use

Negative Results

• Do not regulate flow – pedestrian presses button and walks, but does not know that driver is alerted
• Not as effective as traffic signal, where green/red light is more authoritative
• Does not control right of way – pedestrian assumes they press and walk
• Does not balance flow – at schools, many single crossings rather than a group regulated by time

 

“Speed Tables” are vertical deflections – raised area across road width, slight curvature to discourage speeding. Primary different between this and a Speed Hump is the length – these are designed to support the entire length of an emergency vehicle to avoid grounding. For more details see NACTO

Positive Results

• May slow speed slightly

Negative Results

• Slow response time of emergency vehicles
• May divert traffic to parallel residential streets; and
• Possible increase in noise and pollution for residents living immediately adjacent to the speed bumps.

 

“Speed Humps” are vertical deflections – raised area across road width, slight curvature to discourage speeding. Another variation of this is the Speed Table. For more information see NACTO

Positive Results

• May slow speed slightly

Negative Results

• Slow response time of emergency vehicles
• May divert traffic to parallel residential streets; and
• Possible increase in noise and pollution for residents living immediately adjacent to the speed bumps.
• Possible grounding of long wheelbase vehicles

 

“Road Diets” remove traffic lanes and replace with bike lanes. Typically a four-lane road is changed to two-lane with or without a center turn lane. Claims made are that collisions reduced 19% to 47%, however, these results lack supporting evidence in urban environments, since maximum results seen in rural areas, where actual collision rate was low. Use of percentages distorts the real benefit in actual numbers.

Despite the suggestion that road diets improve safety, according to the Federal Highway Administration:

• Crash rates did not change significantly from the before period to the after period.
• Road diet conversions did not affect crash severity.
• Road diet conversions did not result in a significant change in crash types.

Additionally, they note that “There is a need for future safety and operational studies, under a range of traffic volumes and other conditions, to help identify the situations where road diets would be appropriate. In addition, traffic operations and capacity must be considered fully at a given site before implementing road diets and other lane reduction measures.”

They also indicate that road diets are not suitable for roads with average daily traffic above 20,000 vehicles because “for road diets with ADTs above approximately 20,000 vehicles, there is a greater likelihood that traffic congestion will increase to the point of diverting traffic to alternate routes.”

Positive Results

• Provide a dedicated lane for cyclists

Negative Results

• Do not improve bike incidents at intersections
• Do not improve bike incidents at left turns
• Do not improve bike incidents in business areas where parked traffic backs out
• Increases rear-end collisions for vehicles
• Increases road range – several have been backed out:
  • Playa del Rey, CA

 

“Curb Extensions” or “Bulb-Outs” extend the sidewalk to reduce the distance for pedestrian crossings For more details see NACTO

Positive Results

• Allow for shorter crossing distances

Negative Results

• Reduces road capacity
• Not as effective as traffic signal controlled crossings