Traffic Calming, Speed Calming and Road Safety

Introduction and Background

Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists.

Urban planners and traffic engineers worldwide have many strategies for traffic calming and we would like to share some of these strategies on the Arrive Alive road safety website.

Traffic calming was originally justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic.

However, it is now recognized that streets have social and recreational functions which are severely impaired by car traffic. 

For much of the twentieth century, streets were designed by engineers who were charged only with ensuring traffic flow and not with fostering the other functions of streets. The basis for traffic calming is broadening traffic engineering to include designing for these functions.

Traffic Calming in South Africa

During the development of the Arrive Alive website we have received several requests from the public pertaining to “speed calming” and how they should go about requesting speed humps in their residential areas. 

We have decided to raise this with the experts and are pleased to share information from a presentation by Willem Badenhorst. The main source of information credited for the content  is “Traffic Calming and Road Safety Course, South African Road Federation, Author Jan Coetzee, Pr Eng, ITS Consulting Engineers”

The South African Dilemma

In South Africa we have a prioritization system for traffic calming as we do not, like most authorities, have enough funds in the budget to implement all the traffic calming measures which transport authorities are requested to implement. This used for active traffic calming measures such as speed humps, raised pedestrian crossings and mini-circles.

These requests come from the following sources:

• Requests from the public (including petitions)
• Requests from Councillors
• Requests from other staff members
• Own observations

Where not to implement Traffic Calming 

City Planners and road engineers will generally implement traffic calming ( speed humps, raised pedestrian crossings and mini-circles) only if none of the following is applicable:

• Not in front of entrances
• Not in shade of trees and other physical objects during the day
• Not where they are not illuminated by street lighting at night
• Not on gradients in excess of 8 %
• Not on gravel roads (cannot be painted and there is usually no street lighting)
• Not on Class 4 or higher Class roads although we sometimes implement mini-circles on such streets
• Not within a specified distance of other control mechanisms such3as traffic signals etc

Also please remember that usually they should not be installed as traffic calming measures if they cannot be painted on the same day and often teams have instructions not to leave the site if the measure is not painted and all signage is erected.

Why do people ask for traffic calming?

It is interesting to note that, even though many motorists complain about speed enforcement and are not happy when they receive the dreaded traffic fine, many are voluntarily requesting for speed calming in their neighbourhoods. But why do they ask for traffic calming?

Traffic Calming is most often necessitated by:

• Too high speeds
• Pedestrian / Vehicle conflict (+/- 95%)
• Reckless driving 
• Impact on safety and quality of life

What are the objectives and goals of Traffic Calming/ Speed Calming?

To better understand the importance of traffic calming and the role that it plays in enhancing road safety, we would like to focus on the objectives and goals of traffic calming.

The Traffic Calming Objectives are:

• Reduce speeds of vehicles 
• To increase road safety

(Pedestrian / vehicle conflict decreases)

• Reduce number of vehicles  
• To increase quality of life

(Fewer vehicles cause less irritation)

Goal of Traffic calming

The goal is to improve road safety, enhance quality of life but not impairing mobility too much.

This is achieved by:

• Physical intervention but can include other interventions
• Engineering, Education and Enforcement

Principle of Traffic Calming

There are a few important principles to keep in mind when considering traffic calming.

The Main Principles of Traffic Calming are:

• To reduce speeds
• To lower traffic volumes
• To increase driver alertness

Traffic Calming Policy Goals

Traffic Calming Must: 

• Be part of overall transport strategy
• Improve the efficiency of the road network
• Protect residential areas
• Improve road safety

What is the Purpose of a Traffic Calming Policy?

• To ensure that all traffic calming problems are evaluated in a uniform way
• To clearly define where on the road network traffic calming is allowed
• To describe traffic calming techniques which will be allowed in an area
• To define when traffic calming will be warranted
• To outline the process that should be followed in evaluating and approving traffic calming facilities

A Traffic Calming Policy should contain:

• Road Hierarchy
• Road classes where traffic calming will be allowed
• Routes where NOT allowed (emergency and bus routes, crescents)
• Minimum speeds and traffic volumes before traffic calming is contemplated
• Techniques which will be allowed
• Funding mechanisms

What are the Principles of a Road Hierarchy?

Principles to be adhered to:

• Facilitate certain trip length on correct class of road – linked to mobility
• Road geometry should be linked to class of road
• Accommodate adjacent land use – eg no through traffic in residential areas
• High-order roads should not intersect with low-order roads, eg Class 4 should have no interchange with freeway
• Pedestrian facilities linked to the class of road (No pedestrians on freeway - Class 1 Road)

Road Class and Traffic Calming

ROAD CLASS	Type	Description	Traffic Calming
U1	Freeway	High mobilty, no or very limited at grade access	None
U2	Major Arterial/ Regional Distributor	High Mobility, limited at grade access (intersections) no direct property access	None
U3	Arterial / Major Collector	Balanced mobilty, and accessibility function – typical direct access in older suburbs	Traffic calming to consist only of signage and road makings (not physical)
U4	Collector	More accessibility, less mobilty, direct property access	All types, but with focus on mini-circles iso speed humps
U5	Local Street	Less mobility, more accessibilty	All types, but with focus on speed humps and aesthetically pleasing elements such as paved areas
U6	Pedestrian streets Woonerf	Very limited accessibility and mobility for vehicles but high accessibility and mobilty for pedestrians and cycles	To restrict access for vehicles

Application of a Road Hirarchy

Functional Classifiaction	Traffic Calming	Pedestrian	Parking (on street)	Informal Trading	Public Transport Facilities	Security Villages (roads closed)	Access Spacing	Design Speed
U1	No	No	No	No	No	No	1,6 – 2,4 km  (grade seperated)	120
U2	No	Limited	No	No	Limited	No	0,6 – 1,2 km (can be grade seperated)	100
U3	No Physical	Yes	No	No	Yes	No	0,5 km – 60kmh 0,6km – 70 kmh	80
U4	Limited	Yes	Limited	Limited	Yes	Limited	< 100 m	60
U5	Yes	Yes	Yes	Yes	Yes	Limited	< 50 m	60
U6	Can have	Yes	Very Limited	Limited	No	Limited	< 50	20

Road Layout in new Developments

Every new development should in the design of infrastructure and focus on transport and movement within such development include a special focus on safety and especially the potential for conflict between vehicular movement and that of pedestrians.

When approving plans for new townships road and planning engineers need to check for:

• Address traffic calming – correct time
• Road connectivity based on hierarchy (only two classes up)
• Ensure that road class corresponds to expected traffic volumes
• No long straight sections
• Limited steep gradients
• Provision for pedestrians
• Provision for public transport
• NO Speed humps  to be constructed with roads
• Narrow residential streets (5,5 to 6m maximum)
• Woonerf concept / Security villages / Enclosed neighborhoods

Traffic Calming and the Law

Whenever there is construction and the rights of citizens are affected, we need to be aware of possible legal implications. Engineers might not always be fully aware of the legal realm in which

 they operate!

Why are legal issues important?

• Physical obstructions are placed in the roadway:

If a vehicle is damaged or a person is injured by this obstruction – the question will be asked “who is liable?”

If a roads authority is aware of an unsafe traffic situation (such as speeding taking place outside a school) and someone is injured or killed and nothing is done, the legal people will consider the question “can the roads authority be liable?”

Traffic Calming and Common law issues

Where there is no direct legal prescription and law regulating a specific aspect the common law principles will apply.

Whether an action is deemed to have been intentional or negligent can be established by way of the common law.

Negligence of person or entity (eg roads authority) WILL be tested against “reasonable man test”

This will determine if the applicable authority would have been able to foresee that the traffic calming device could have caused an accident.

It will further determine if the authority could have foreseen that an accident could have happened if the device had not been installed 

Applicable Legal Documents

The legal principles around traffic calming are best to be considered with reference to the following legal documents.

Road Traffic Act (Act 93 of 1996)

• PRINCIPLES (“POLITICAL”)

Chapter VII – Road Safety

Chapter IX  - Road Traffic Signs and general speed limit

National Road Traffic Regulations

• LEGAL TECHNICAL

Chapter IX  - Road Traffic Signs and general speed limit

Refer to SADC Manual, SABS Codes

SADC Road Traffic Signs Manual (SADC Manual)

• ENGINEERING TECHNICAL

Municipal By-laws

Common Law

SADC Road Traffic Signs Manual - Contains details of road signs and road markings to be used with traffic calming

Following the Manual will ensure consistency

To deviate from manual – have very good reason (in other words, do not deviate)

Also View:

Pedestrian Safety Hints

Speed as a Contributory Factor to Road Traffic Crashes

Scholar Patrol and Road Safety

Traffic Calming and Pedestrian Safety