§ 78-106. Types of traffic calming devices.

Various types of traffic calming devices/techniques are presented in this section. They are presented and categorized according to their suitability to correct problems associated with each type of neighborhood traffic problem. Some of these devices have been shown to be effective in solving one or more types of traffic-related problems. Results of studies released through the Institute of Transportation Engineers (ITE) of technical papers, indicate that the following were quite effective in residential speed control. These are speed humps, traffic circles, traffic chokers, and traffic diverters. Others mentioned later are suited to correcting problems associated with cut-thru traffic and pedestrian safety.

(1)

Speed humps (speed reduction device).

a.

Purpose: To reduce vehicle speeds.

b.

Effectiveness: 22-foot speed humps are very effective at encouraging 30 mph vehicle speeds.

c.

Advantages:

1.

Effectively reduce vehicle speeds.

2.

It poses no restrictions for bicycles.

3.

Does not affect intersection operations.

d.

Disadvantages: Can possibly increase traffic noise from braking and acceleration of vehicles, particularly buses and trucks.

e.

Cost: Between $2,500 and $3,500 each.

f.

Transit service impacts: Experience shows 22-foot speed humps do not impede transit services or scheduling.

g.

Emergency services impacts: When speed humps designs are selected for any street, one must consider whether it is used as a primary response route.

h.

Other considerations: Speed humps are not considered on grades greater than eight percent.

(2)

Chicane (speed reduction device).

a.

Description: A feature that changes the physical characteristics of a roadway section from an existing straight alignment to a series of horizontal curves.

b.

Purpose: To reduce the speed of vehicles by providing a narrowed vehicle travel path for a section of roadway.

c.

Advantages:

1.

Reduces vehicle speeds with less impact on emergency service vehicles.

2.

May reduce cut-through traffic.

d.

Disadvantages:

1.

Most residents would have driveway affected by the type of installation.

2.

Increased maintenance for landscaping and pavement.

3.

Significant loss of on-street parking.

e.

Cost: Between $5,000 and $10,000 per location.

f.

Transit service impact: Impact not significant.

g.

Emergency service impacts: Impact not significant.

h.

Other considerations: N/A.

(3)

Radar trailer (speed reduction device).

a.

Description: A portable radar speed meter capable of measuring vehicle speed graphically and displaying the speed of the motorist.

b.

Advantages: Speeds may be reduced during short intervals where the radar trailer is located.

c.

Disadvantages:

1.

Not an enforcement tool.

2.

No noticeable effect on deterring rat-running traffic.

d.

Cost: N/A - County purchasing and operates.

e.

Transit service impacts: N/A.

f.

Emergency service impacts: N/A.

g.

Other services: N/A.

(4)

Narrowing lanes (speed reduction device).

a.

Description: Striping is used to create narrow travel lanes to 10-foot wide lanes. This gives drivers the feel of a narrow street that does not lend itself to high speeds.

b.

Purpose: To restrict the width of available road space.

c.

Advantages:

1.

Speed may decrease and safety is improved through the provision of positive guidance to drivers.

2.

The striping can be easily modified if paint is used.

d.

Disadvantages: Residents do not always perceive striping to be an effective tool for speed reduction.

e.

Cost: The cost varies on the length of a street.

f.

Transit service impact: It will not have significant impact.

g.

Emergency service impacts: It will not have significant impact.

h.

Other considerations: N/A.

(5)

Diagonal diverter (reduce cut-through traffic).

a.

Description: A barrier between diagonally opposite corners of a four-legged intersection, thus creating two unconnected L-shaped intersections.

b.

Advantages:

1.

Effectively reduces cut-through traffic.

2.

Creates no dead-end streets, local residents and service vehicles may view this as a benefit in that their routes can be more direct.

3.

Reduces motorist speed.

4.

Can restrict access while retaining bicycle and pedestrian access.

c.

Disadvantages:

1.

In a large neighborhood, can shift problems elsewhere unless a strategic pattern of diverters are used.

2.

May inconvenience local residents who are forced to drive longer more circuitous paths to and from their homes.

d.

Cost: Approximately $15,000 to $35,000.

e.

Transit service impacts: Should not be considered on transit streets.

f.

Emergency service impacts: Even though diagonal diverters would restrict turns to EMS vehicles, they can be designed and installed to provide for emergency access.

g.

Other considerations: N/A.

(6)

Semi-diverters (reduce cut-thru-traffic).

a.

Description: A barrier to traffic in one direction of a street which permits traffic in the opposite direction to pass through.

b.

Advantages:

1.

Serve as an alternative to a one-way street designation by allowing residents within the block to continue to use the street for two-way travel opportunity.

2.

Emergency service vehicles travel time is expedited.

c.

Disadvantage: Because they block only one-half of the street, these are easily violated.

d.

Cost: $5,000 to $20,000.

e.

Transit service impacts: May affect transit routes, however, careful planning will be incorporated to minimize any effects.

f.

Emergency service impacts: Allows a higher degree of emergency vehicle access than cul-de-sacs or diagonal diverters can be designed to allow emergency vehicle access, but careful consideration needs to be given to their use on primary fire response routes.

g.

Other considerations: N/A.

(7)

Median barrier (reduce cut-thru traffic).

a.

Description: A physical barrier on a non-local street which can effectively eliminate left turns from that non-local street onto a local street and eliminate local street straight-through and left turn traffic across the non-local street. A median barrier usually is an asphalt/concrete curbed island with or without a decorative landscaping and surface treatment.

b.

Advantages:

1.

Makes the intersection move safely by reducing the number of conflicting movements.

2.

Reduces local street volumes.

3.

Negates the possible need for future expensive traffic signal.

c.

Disadvantages:

1.

The physical barrier may sift traffic to other locations where left-turn opportunities exist.

2.

This tool may inconvenience local residents who will be forced to drive longer more circuitous paths to reach their destination.

d.

Cost: Cost vary widely.

e.

Transit service impacts: Transit routes will be planned to accommodate median barriers so the effect should be minimal.

f.

Emergency service impact: Consultations with emergency service providers will take place before median barriers will be installed. Careful planning of these facilities should minimize any negative impact.

g.

Other considerations: A full median with no breaks can also be used to prohibit all left turns.

(8)

Culs-de-sac (reduce cut-thru traffic).

a.

Description: Complete closure of a street either at an intersection or at a mid-block location.

b.

Advantages:

1.

Very effective at eliminating most of the previously speeding traffic on the block.

2.

Very effective at reducing volumes.

3.

Can be landscaped for an attractive effect to convey street discontinuity.

4.

Improves traffic safety.

c.

Disadvantages:

1.

Can negatively affect response times for emergency service.

2.

In large neighborhoods, can shift a problem elsewhere unless a strategic pattern of cul-de-sacs are used.

3.

Can generate confusion on the part of users unless signed carefully.

4.

May inconvenience local residents.

d.

Cost: $20,000 each.

e.

Transit service impacts: Should not be placed on transit routes.

f.

Emergency service impacts: Emergency service providers will be consulted before these are installed.

g.

Other considerations: Inhibits provision of emergency services, but can be used using break away posts.

(9)

Chokers (reduce cut-through traffic).

a.

Description: Narrowing of a street at an intersection, mid-block or a segment of a street in order to reduce width of the traveled way by construction of a wider sidewalk or landscape strip.

b.

Advantage:

1.

Slight slowing is normally the result.

2.

Shorter pedestrian crossing distances and better motorist-pedestrian visibility of each other.

3.

Can discourage truck entry.

c.

Disadvantages:

1.

Potential obstacle for motorist to run into.

2.

May impede bicycle mobility and safety.

3.

May require reworking of surface drainage.

4.

May result in loss of curbside parking.

d.

Cost: $7,000 to $10,000 each.

e.

Emergency service impacts: The impact should not be significant.

f.

Transit service impacts: Doesn't impede service, but might affect scheduling.

g.

Other considerations: Chokers will be 14 to 16 feet wide.

(10)

Raised crosswalks (pedestrian safety).

a.

Description: Crosswalks constructed 3 to 4 inches above the elevation of the street.

b.

Purpose: Intended to reduce vehicle speeds specifically where pedestrians will be crossing a street.

c.

Effectiveness: Effective at reducing vehicle speeds.

d.

Cost: Between $2,000 and $5,000 each.

e.

Noise impact: May generate noise from vehicle decelerating and accelerating.

f.

Transit service impacts: N/A.

g.

Emergency service impacts: N/A.

h.

Other considerations: Consideration for visually impaired persons dictates not placing the raised crosswalk at the same elevation as the sidewalk. Though the crosswalk is raised from the street surface, a pedestrian should also be able to tell when they are entering an area shared with automobiles.

(11)

Curb extensions (pedestrian safety).

a.

Purpose: Employed to make pedestrian crossing easier and to narrow the roadway.

b.

Effectiveness: Improve pedestrian safety by reducing the street crossing distance and improving sight distance. These may also slightly influence driver behavior by changing the appearance of the street. They can be installed either at intersections or midblock.

c.

Advantages:

1.

Reduce pedestrian crossing distance and time.

2.

Make pedestrian crossing points more visible to drivers.

3.

Prevent vehicles from passing other vehicles that are turning.

4.

May visually enhance the street through landscaping.

5.

Does not slow fire vehicles.

d.

Disadvantages:

1.

Require some parking removal.

2.

May make it difficult to accommodate full bicycle lanes.

e.

Cost: Between $7,000 and $10,000.

f.

Transit service impact: Enhance service by moving the curb so riders step directly between the sidewalk and bus door.

g.

Emergency service impacts: N/A.

h.

Other considerations: N/A.

(Ord. No. 98-1103, §§ 4.0—4.11, 9-2-98)