FAQs from April Webinar, Traffic Calming: Present and Future

These answers were provided with the collaborative efforts of Professor Reid Ewing and the staff and engineers of Traffic Logix.


Are the various signs shown identified by the MUTCD?

There are some traffic calming signs that are recognized by the MUTCD. Other signs are left to the discretion of the traffic engineer.

What studies have been conducted to see if traffic increases speed after the physical calming device is removed?

Before and after speeds studies are conducted at a particular location for a period of time. There are many examples and some are summarized in the new book co-authored by Reid Ewing, the US Traffic Calming Manual.

When was the last time this manual was updated?

ITE published Traffic Calming: State of the Practice in 1998. In August of 2007, ITE published Guidelines for the Design and Application of Speed Humps. Professor Reid Ewing and Steve Brown published the US Traffic Calming Manual in 2009.

Speed Cushions

What are the disadvantages of speed cushions / speed lumps?

People are sometimes not familiar with them, which can create a longer learning curve.

What are the drainage concerns?

This issue is minimized due to smaller non-continuous design and when using rubber they still allow a small portion of water to pass through and under the product.

Don't non-emergency vehicles try to straddle over them?

When placed properly, cars cannot straddle them. Only emergency vehicles with wider custom chassis can do so.

Do they traverse counter-flow?

Speed cushions have a bi-directional design, however they do have specific orientation.

When installing speed cushions on a wide street with bicycle lanes and parking lanes, so that there is the potential of vehicles going around the vertical device, do you recommend extending the speed cushion into the bike lane and/or parking lane?

Speed cushions can be extended into bike or parking lanes at the discretion of the engineer.

We are proposing the use of speed cushions however our Fire Department is objecting because the spacing of the dual rear wheels on their response vehicles is such that they go over the raised portion and require them to slow down too much. If we change the spacing between the lumps, they will not be effective for passenger SUVs. How do other communities get around this?

In our experience with emergency response agencies around the country, the impact of speed lumps on response time is minimal.You can see a sample approval letter here.

Do passenger vehicles tend to use center of road when speed lumps are installed?

If speed cushions are installed properly, passenger vehicles will not be able to avoid them.


We have a significant portion of traffic cheating through our speed cushion channels just like Fire vehicles. Any suggestions?

Properly designed speed cushions should not allow space for passenger vehicles to 'cheat' through the speed cushion channels. With rubber cushions, you can easily modify the design if any problems are encountered.

What is the recommended spacing for speed 'bumps' in a public parking lot to achieve 10 mph speeds?

200 feet is the recommended spacing, although this may differ based on the size of the speed bump.

What measures would you recommend for a two-lane rural-type road with no curb and dirt shoulder?

Vertical measures such as speed humps, tables, or cushions are effective for most application areas.

What is your opinion about incorporating landscaping into a traffic calming device?

Aesthetics is an important part of traffic calming as long as it does not impact drivers' line of sight.

How would you suggest addressing concerns about hazards presented by the presence of landscaping?

If landscaping is posing a danger, it is important to adjust the landscaping to ensure it does not inhibit driver vision or create any other hazard.

We are working with a jurisdiction who is on the fence regarding incorporation of landscape for fear that it might create a hazard in the operation/traffic functionality of the device. I think without landscaping, it makes it harder to incorporate the device into residential streetscapes (just one planner's opinion). What is your opinion?

Traffic calming should always incorporate aesthetics. When including landscaping, it must be planned properly to ensure safety.

Design of horizontal measures

Once 'R' is determined for a travel path, is there a method of offsetting a desired lane width?

R is a calculation of travel path that is not an offset, but rather a deflection that follows the AASHTO ' Green Book principles.

Alternate Methods

Did you consider all-way stop as a calming measure?

Unwarranted stop signs should never be used to control speed.

Could there be some discussion of community gateways and their effectiveness on cut through traffic?

Gateways can be an effective way to discourage cut-through traffic.

Are reverse spikes considered traffic calming devices?

No. These are for limited Police/Ramp Meter, private lot or similar applications only.

Will a change in crosswalk texture or material (without a horizontal change) serve as a traffic calming device?

While texture can add to crosswalk aesthetics, they typically have little impact on speed.


What is the feedback from snow plowing operations with regard to speed humps, etc.?

Most plow operators prefer to not have traffic calming devices on the road. Rubber speed humps provide a solution to this issue since they can be removed during the winter.


Regarding center islands and the picture showing the double yellow line simply being shifted to right side of island, given Section 3B.10 of the 2009 MUTCD referring the reader to Figure 3B-15 showing hatching, do you recommend that we start using hatching?

This is a 'shall' in the MUTCD, so you should already be doing this.

What's your opinion about Optical Speed Bars as a traffic calming measure?

Some studies have shown them to be effective while others have shown them to be ineffective.

Lane Narrowing

For narrowing/neck-downs, how narrow would you recommend to go?

10ft is often the lower limit, in some cases you have to consider rear wheel tracking which will increase widths somewhat.

Can you comment on reducing vehicle lane widths (e.g., 12-foot lanes narrowed to 10-foot lanes)?

Lane narrowing is an effective tool to reduce vehicle speeds; however care must be exercised so as to not reduce recommended lateral clearances which would then promote 'side-swipe' accidents.

Why do you think striping/ narrowing the lane width is not effective?

Lane narrowing does not impact vehicle speeds, it is the drivers' perception/reaction to lane width that may or may not affect how they operate their vehicles.


What is your opinion of chokers that restrict access to only one vehicle per direction at a time?

Chokers can be an effective tool when used properly.


Are there any examples applying the process/devices/intersections in retirement communities?

Radar signs are more popular as traffic calming devices in retirement communities.

Have any of these devices been endorsed by the ADA?

Speed tables and other traffic calming devices can be ADA compliant when installed properly.


When it comes to implementing a neighborhood traffic calming plan, how much does it typically cost to build the required numbers of horizontal and vertical measures?

Costs of building traffic calming devices vary across the country based on labor and materials.

Which types of horizontal and vertical measures are most cost effective?

Vertical measures are the most effective measures in reducing speed and therefore the most cost effective. Speed cushions cost less than other vertical measures and can therefore be considered the most cost effective tool.

Should neighborhoods pay for their own traffic calming devices?

In the 90's, of 20 jurisdictions studied, most would not allow residents' to pay since poor neighborhoods were then at a disadvantage. The one exception is that if 'rich' areas wanted fancy features, cities would pay for the basic design and any extras were then covered by neighborhood members. In 2004, there was found to be more acceptance of neighborhoods either paying through donations or special assessments. The Sacramento County study of 20 city/counties found that it was not unreasonable for residents to pay.

Is there federal funding available for traffic calming?

The Transportation, Community and System Preservation Program (TCSP) will fund Traffic Calming. Safe Routes to School (SRTS) provides funding as well. New laws are going to be even more permissive where physical inactivity is linked to speeding on local streets where children play and parents walk. Climate change is also linked to the effects from speeding traffic and traffic calming can be effective in making walking or biking effective alternatives.


What is the web site that the speaker is referencing?


Will this presentation be available electronically?

Yes, Click here to download the PDF
This article discusses:

SafePace 100 Compact Entry-Level Speed Sign SafePace 400 Standard Your Speed Sign SafePace 550 Variable Speed Limit Sign SafePace 600 Variable Message Sign Speed Humps Speed Tables Speed Cushions SuperFlex Curbing