TO: Mayor and Members of City Council
THRU: Adam Lindsay, Assistant City Manager
FROM: Sheila Thomas-Ambat, PE, CCM, CFM, Public Services Director
Brian McGill, PE, PTOE, City Traffic Engineer
DATE: November 6, 2023
RE:
Title
Traffic Calming Measures
end
COUNCIL DISTRICT(S):
Council District(s)
All
b
Relationship To Strategic Plan:
Goal I: Be a safe and secure community.
Goal II: Be a responsive city government supporting a diverse and viable economy.
Goal III: Be invested in today and tomorrow.
Goal IV: Be a highly desirable place to live, work, and recreate.
Goal V: Be a financially sound city providing exemplary city services.
Goal VI: Have a collaborative citizen and business engagement base.
Executive Summary:
The purpose of this report is to address and discuss the request received from Council to provide high-level information on traffic calming measures outside of speed bumps. The majority of traffic calming measures fall into three categories: Horizontal deflection, vertical deflection, and street width reduction.
Horizontal deflection prevents drivers from driving in a straight line and includes the following traffic calming measures:
• Lateral Shift
• Chicane
• Realigned Intersection
• Traffic Circle
• Mini Roundabout
• Roundabout
Vertical deflection changes the road height and includes the following traffic calming measures:
• Speed Bump/Hump
• Speed Cushion
• Speed Table
• Raised Crosswalk
• Raised Intersection
Council requested speed bumps/humps be omitted from this report, however to be thorough, speed bumps/humps were included in this report and the attachments.
Street width reduction narrows the travel lane, making it less comfortable for the driver to speed, and includes the following traffic calming measures:
• Corner extension/bulb-out
• Choker
• Median Island
• On-Street Parking
• Road Diet
Other measures were reviewed after the initial administrative report was submitted to Council, and are included for the presentation. These measures include the following:
• Radar Feedback Signs
• Rumble Strips / Stripes
• Multi-Use Lines / Lanes
Traffic calming measures not reviewed for this report include the following: Traffic signals, pavement markings, gates, corner radius reductions, streetscaping/landscaping, textured pavements like brick pavers, signs, and temporary measures such as police speed enforcement. Studies have shown that signs are not an effective traffic calming measure.
Background:
- City Council requested staff review traffic calming measures outside of speed bumps at the conclusion of the August 7th, 2023 City Council Work Session.
- Staff presented City Council with an administrative report at the September 25th, 2023 City Council Regular Meeting, where it was moved to hear the Report as a presentation during a City Council Work Session.
There are multiple contributing factors to speeding, with a large component being driver comfort and confidence in their ability to navigate the road. Successful attempts to effectively reduce speeds have been collectively called traffic calming measures. Traffic calming measures reduce speeds by making drivers uncomfortable when they speed across the installed treatment. The three following measures compose the main body of effective traffic calming measures: Horizontal deflection, vertical deflection, and street width reduction. The following information is a high-level summary of the various treatments under each traffic calming measure.
All costs referenced in this administrative report are based on studies conducted by the Institute of Transportation Engineers (ITE) and Federal Highway Administration (FHWA). We have not adjusted these numbers for inflation, and their values reflect unit costs per installation. Cost is provided to compare the different treatments, with the understanding that costs are subject to change depending on the site and project requirements.
Horizontal Deflection prevents drivers from being able to drive in a straight path on a road. By forcing drivers to turn and adjust their path, they have to reduce their speed to remain comfortable.
• Lateral Shift
A lateral shift moves, or offsets, the road in typically one direction. Appropriate for nearly all road types, emergency vehicles and transit vehicles don’t have issues with this measure. This treatment has limited research information on its impact on speeding, so it may not be as effective as other measures. Costs (2017 dollars) $8k - $25k.
• Chicane
A chicane is a road offset occurs more than once, like a lateral shift that is back-to-back. This treatment is appropriate for residential roads, and depending on spacing, can slightly slow-down emergency vehicles and transit vehicles. It is effective at reducing speed, but drivers may ignore pavement markings to drive straight. Costs (2017 dollars) $8k - $25K.
• Realigned Intersection
This treatment reconfigures an intersection to have skewed approaches. It is appropriate for residential roads of low speed, and primarily for T-intersections. This can be imagined as a Chicane at a T-intersection, with more space between the road offsets due to the intersection. This treatment has little impact on emergency vehicle response times and transit vehicles. Costs (2017 dollars) $15k - $60k.
• Traffic Circle
Not to be confused with a roundabout, this treatment places an island in an intersection which is usually landscaped or decorated, and should not be used for intersections where large trucks or buses often turn left. This is for intersections where modern roundabout principals cannot be applied. A traffic circle typically does not have splitter islands/ deflection preventing vehicles from entering the circle against the flow of traffic. This means vehicles could technically make a left-turn against traffic in the circle. Some jurisdictions permit fire engines and transit buses to make the left-turn in front of the circle if there is no traffic present as the larger vehicle typically cannot circulate the island. This measure is appropriate for less-heavily traveled roads and residential roads, and sees many of the same safety benefits as a roundabout. Costs (2017 dollars) $10k - $25k.
• Mini-Roundabout
Similar to a roundabout, but with smaller diameter and a mountable island. This treatment has one lane in each direction, and the center island is fully traversable so that emergency vehicles and transit vehicles may drive over the center island for left turns at slow speeds. This intersection is not an appropriate type for intersections with a lot of heavy vehicles and buses making left-turns. It is appropriate for most road types, although it is not typically used for major thoroughfares. Costs (2017 dollars) $15k - $60k+.
• Roundabout
A raised island which requires drivers to slow, yield to traffic in the intersection, and then circulate the island to complete their movement. Generally considered safer than signalized and stop-controlled intersections. Has a limit to the number of lanes that can be accommodated, as well as the volume of traffic it can handle during peak times. Can be used to replace a traffic signal. If used to replace a City-owned traffic signal, would reduce maintenance costs, and would eventually increase revenue from Municipal Agreement under NCDOT Schedule C & D. Appropriate for all road types, but not typical for intersections inside of neighborhoods. Costs vary wildly based on retro-fit versus new construction costs, but recent 2017 dollars have estimates range from $150k - $2M+.
Vertical Deflection creates a change in the roadway height, forcing drivers to slowdown. Council requested that we review traffic calming measures outside of speed bumps, and vertical deflection includes speed bumps/humps. To provide a complete picture of vertical deflection options and document information for future review by others, speed bumps/humps were included in this report and the attachments. Vertical deflection includes the following measures:
• Speed Bump/Hump
A 3 to 4 inch raised area that forces drivers to reduce speed or else they experience discomfort. This type of treatment impacts emergency response time as it delays fire trucks and ambulances, but it does not impact access to driveways. One of the most cost-efficient ways to reduce speeding, but only suitable for less-heavily traveled roads, residential roads, and roads with lower speeds. Costs (2017 dollars) $2k - $4k.
• Speed Cushion
Raised areas that are identical to speed bumps/humps, with gaps between raised areas located to allow the wheels of wider fire engines higher speeds across the cushion. A detriment of this treatment is that collective experience shows drivers of standard vehicles favor driving with one of their wheels aligned with the gap in the cushion which can lead to “close calls” with on-coming traffic. Motorcycles also use the gap without reducing speed. This treatment is appropriate for collectors and residential roads. Costs (2017 dollars) $2.5k - $6k.
• Speed Table/Raised Crosswalk
Speed bump/hump with a flat top, often used in an area with a lot of pedestrian activity or where pedestrian visibility is a priority. This treatment is also useful when reviewing place-making opportunities and trying to serve pedestrian safety concerns, like the downtown area, but less suitable for higher-speed roads. This measure also has a sizable crash rate reduction on treated streets. This treatment is not favorable for emergency access vehicles, and causes delays similar to speed bumps/humps. Costs (2017 dollars) $4k - $8k.
• Raised Intersection
The road rises to sidewalk level, and generally makes the intersection more pedestrian-accessible. This measure is normally observed in densely-developed urban areas, and part of a broader area-wide traffic calming scheme with very high pedestrian crossing demand. This measure is not suitable for high-speed roads or major thoroughfares. This treatment is not favorable for emergency access vehicles, but is not as impactful as speed bumps/humps. Costs vary wildly based on the site however research provides a 2017 dollars’ estimate of $15k to $60k and higher per treatment.
Street Width Reduction narrows the width of the lane of travel, increasing “side-friction.” A sense of “side-friction” is when drivers sense that a lot is going on at the street level, - i.e., vehicles parking, pedestrians walking - and the drivers should reduce speed and anticipate other road users. “Side-friction” is more present on Hay Street than on Skibo Road. These measures can also provide other benefits like increasing pedestrian safety, place-making, and providing parking for businesses or outdoor space for seating. Street width reduction includes the following measures:
• Corner extension/bulb-out
An extension of the sidewalk into the road, resulting in a narrower roadway. This reduces the distance pedestrians need to cross an intersection, and is appropriate for all road types. Vehicle speeds may not be reduced as effectively as other treatment options. The two main challenges for this treatment is drainage and visibility of the curb delineation. Emergency and transit vehicles should not have an issue with this treatment. When applied to all corners of a four-legged intersection, 2017 dollar estimates begin at $8k and increase to $40k or more if drainage is an issue.
• Choker
Essentially a corner extension/bulb-out that is placed at a mid-block location, or where there is not an intersection. Can be used to narrow the shoulder, or can be used to pinch a two-lane road down into a one-lane segment at a specific location with a “one-lane choker”. A one-lane choker forces two-way traffic to take turns going through the pinch point. This would be similar to a one-lane bridge on a two-lane road. Appropriate for all road types and mainly lower speeds, but may not reduce as effectively as other treatment options depending on application. Emergency and transit vehicles should not have an issue with this treatment. Costs (2017 dollars) $10k - $25k.
• Median Island
A raised island along the street centerline that narrows the travel lane. This can be used as a pedestrian refuge when used at a pedestrian crossing, and also with a Choker which can help reduce speeds more efficiently. Driveway access in relation to the median is always a concern. Studies have shown that there is no significant impact on speed reduction beyond the median island. Cost is a direct function of length and width of median island and research estimates place typical 2017-dollar estimate at $15k - $55k per treatment.
• On-Street Parking
Providing on-street parking narrows the road when vehicles are parked. This can also be used as a place-making tool to provide parking opportunities to nearby land uses. A challenge arises when parking is not used, that drivers may feel more comfortable speeding through the area. There’s also the concern of drivers maneuvering between active traffic and parking. This treatment is appropriate in most settings on most roads, but should be reviewed on a case-by-case basis instead of applied with broad strokes. Parking should not be considered near traffic circles, roundabouts, or where it could create safety hazards at intersections. Costs vary based on length of application, and is open to interpretation, with one estimate placing the cost at $5k-$10k per newly paved space, and another placing the cost at $250 per retrofitted parking space for a road diet.
• Road Diet
Reduces the existing number of lanes or their lane width through paint or physical changes. This often occurs with four-lane roads being converted to three-lane or two-lane roads, with improvements suggested along the segment or corridor. The improvements typically associated with a road diet include bicycle lanes, multi-use paths, two-way left-turn lanes, pocket turn-lanes, on-street parking, raised medians, sidewalks, and many other improvements. This treatment is suitable for nearly all road types, all speeds, and benefits all road users. Limiting factor for a road diet is the volume of the road, with an unofficial threshold of 20,000 vehicles per day. While a road diet normally reduces the number of through lanes, mobility (i.e., speed, travel time) can actually improve depending on how the treatment is applied. This type of treatment typically requires a lot of community involvement, and the costs vary wildly as each site is unique and different. Some estimates put a road diet between $10k and $100k+ per mile of road reconfigured.
Other Measures following the completion of the administrative report were identified for inclusion in the presentation. They are as follows:
• Radar Feedback Signs
Radar feedback signs may be permanently pole-mounted, or trailer-mounted, and typically best-supported with police speed enforcement. Literature review provides conflicting results; Some studies indicate that drivers may choose to excessively speed to test the limits of the sign, exacerbating the speeding issues. Permanently mounting a sign with speed enforcement over an area appears to show the most effectiveness over an area. These type of signs are also most effective where speed limits change, as opposed to general reminders of the speed limit. Some estimates currently show the cost of a radar feedback sign at between $3K-$6K each.
• Rumble Strips / Stripes
This road treatment is considered to be a roadway safety feature, and not a speeding countermeasure. Rumble strips are those typically embedded in the shoulder or centerline to alert inattentive drivers to an impending lane departure. Rumble stripes are to alert drivers to a change in roadway conditions, typically associated with a curve or stop-controlled intersection ahead. The costs typically associated with these treatments are between $500 and $6k per mile, and are effective depending on crash concerns.
• Multi-Use Lines / Lanes
An on-road shared-use facility, akin to a paint-only bicycle lane, this measure reduces the roadway width. It provides a shared space for users to walk, bike, park, and otherwise use outside of the travel lane. This type of measure is unique to the City of Fayetteville, and is typically not the first measure to use as a countermeasure to speeding. Estimates place the costs between $5k-$21k per mile, and shows a minor impact on speed reduction.
As the purpose of this administrative report is focused on traffic calming devices, we did not review or present items whose primary measure is traffic flow or safety and secondary impact may be traffic calming. This means pavement markings, gates, or corner radius reductions. Temporary measures such as police speed enforcement are not permanent speed reduction solutions, and are not discussed in-depth this report, although speed cameras in strategic locations may provide some traffic calming where the previously discussed is not possible, such as school zones on major arterials. Streetscaping/landscaping has been shown impact speed reduction as it increases “side-friction”, however this should be considered part of a larger street width reduction strategy or part of a road diet. Textured pavements, such as brick or cobblestone roads, have also been shown to reduce speeds, however the maintenance cost have to be considered. Finally, signs should not be used as a traffic calming device as studies have shown they are not effective.
Issues/Analysis:
N/A
Budget Impact:
N/A
Options:
N/A
Recommended Action:
N/A
Attachments:
Traffic Calming Presentation
Traffic Calming Examples
Traffic Calming Appropriateness Matrix