SPEED HUMPS

 

Description:

• rounded raised areas of pavement typically 12 to 14 feet in length
• often placed in a series (typically spaced 300 to 600 feet apart)
• sometimes called road humps or undulations

Applications:

• residential streets
• not typically used on major roads, bus routes, or primary emergency response routes
• midblock placement, not at an intersection
• not on grades greater than 8 percent
• work well with curb extensions

 

Potential Impacts:

• no effect on non-emergency access
• speeds determined by height and spacing; speeds between humps have been observed to be reduced between 20 and 25 percent on average
• based on a limited sample of sites, typical crossing speeds (85th percentile) of 19 mph have been measured for 3½ inch high, 12 foot humps and of 21 mph for 3 inch high, 14 foot humps; speeds have been observed to rise to 27 mph within 200 feet downstream
• speeds typically increase approximately 0.5 mph midway between humps for each 100 feet of separation
• studies indicate that traffic volumes have been reduced on average by 18 percent depending on alternative routes available
• studies indicate that collisions have been reduced on average by 13 percent on treated streets (not adjusted for traffic diversion)
• most communities limit height to 3-3½ inches, partly because of harsh ride over 4-inch high humps
• possible increase in traffic noise from braking and acceleration of vehicles, particularly buses and trucks

Emergency Response Issues:

• Concern over jarring of emergency rescue vehicles
• Approximate delay of between 3 and 5 seconds per hump for fire trucks and up to 10 seconds for ambulance with patient

Typical Cost:

• Approximately $2,500  

TRAFFIC CIRCLE

 

Description:

• raised islands, placed in intersections, around which traffic circulates
• motorists yield to motorists already in the intersection
• require drivers to slow to a speed that allows them to comfortably maneuver around them
• sometimes called intersection islands
• different from roundabouts

 

Applications:

• intersections of local or collector streets
• one lane each direction entering intersection
• not typically used at intersections with high volume of large trucks and buses turning left

 

Design/Installation Issues:

• typically circular in shape, though not always
• usually landscaped in their center islands, though not always
• often controlled by YIELD signs on all approaches, but many different signage approaches have been used
• key design features are the offset distance (distance between projection of street curb and center island), lane width for circling the circle, the circle diameter, and height of mountable outer ring for large vehicles such as school buses and trash trucks

 

Potential Impacts:

• no effect on access
• reduction in midblock speed of about 10 percent; area of influence tends to be a couple hundred feet upstream and downstream of intersection
• only minimal diversion of traffic
• intersection collisions have been reduced on average by 70 percent and overall collisions by 28 percent
• can result in bicycle/auto conflicts at intersections because of narrowed travel lane

 

Emergency Response Issues:

• emergency vehicles typically slow to approximately 13 mph; approximate delay of between 5 and 8 seconds per circle for fire trucks
• fire trucks can maneuver around traffic circles at slow speeds provided vehicles are not parked near the circle

Other/Special Considerations:

• large vehicles may need to turn left in front of the circle (which could be unsafe at higher volumes); legislation may be required to legally permit this movement
• quality of landscaping and its maintenance are key issues
• landscaping needs to be designed to allow adequate sight distance
• care must be taken to avoid routing vehicles through unmarked crosswalks on side-street approach

Typical Cost:

• approximately $3,500 to $15,000 (varies based on the size of the circle)

 

MULTI-WAY STOP SIGNS

 

Description:

• stop conditions in all approaches of a intersection
• require drivers to come to a full stop

 

Applications:

• intersections of local or collector streets with equal volumes
• intersections with sight distance and heavy pedestrian traffic
• used as combination with other traffic calming devices such as speed humps and traffic circles

 

Design/Installation Issues:

• often supported by stop ahead signs and stop bars for all approaches of the multi-way stop sign intersection

 

Potential Impacts:

• reduced cut-through traffic
• reduce the speeding near intersections if used with other traffic calming devices such as speed humps and traffic circles
• increased vehicular travel times
• increased enforcement cost at unwarranted stop sign locations
• stop compliance is poor at unwarranted multi-way stop signs
• stop signs increases noise in the vicinity of an intersections

 

Emergency Response Issues:

• approximate delay of between 8 and 10 seconds and may require to come to full stop  

 

Typical Cost:

• approximate cost $500.00 per intersection