Traffic Calming – Locations and Options

Traffic calming is primarily required to enhance safety and improve the quality of life in residential and urban areas. The main reasons and locations where traffic calming is typically necessary are as follows:

Residential Areas: To protect residents, especially children and the elderly, from the dangers posed by fast-moving or heavy traffic. Lowering traffic speeds in these areas can reduce accidents and make the environment safer for pedestrians and cyclists.

School Zones: To ensure the safety of children and other pedestrians, traffic calming measures like speed bumps, raised crosswalks, and restricted speed limits are often implemented around schools.

Downtown Areas and Business Districts: These areas typically have high pedestrian traffic. Traffic calming helps in reducing vehicle speeds, enhancing pedestrian safety, and making these areas more attractive for walking and shopping.

Near Parks and Recreational Areas: These areas attract families and active individuals. Traffic calming measures can help in reducing the risk of accidents and making access to these places safer and more enjoyable.

Along Bike Routes: To promote cycling as a safe and viable form of transportation, traffic calming can be used to slow down traffic and reduce conflicts between vehicles and cyclists.

Neighborhoods with High Accident Rates: If certain streets have a history of traffic accidents, traffic calming can be an effective way to reduce these incidents by forcing drivers to slow down.

Traffic Calming Options:

Traffic calming strategies are designed to encourage safer, more responsible driving and create environments that are more accommodating to non-motorised street users.

Most traffic calming measures are made up of a selection of one or more features. These include:

• Speed bumps and speed humps
• Chicanes
• Raised crosswalks and intersections
• Road narrowigs
• Kerb extensions or bulb-outs
• Gateways
• Textured pavements
• Pinch points

Road Humps

The generic term ‘Road Hump’ is used to describe a range of measures which are legal obstructions on the surface of highway, constructed to control the speed of vehicles in build-up areas.

Road humps are constructed in a variety of shapes and sizes to cater to different situations and locations and a traffic calming schemes could include a combination of different types of humps. However, a mix of round and flat top humps could create difficulties for drivers, due to different acceptable speeds of approach to each type of hump.

Road humps can only be used on roads with a speed limit of 30 mph or less.

Types of humps currently in use include:

• Normal flat top humps
• Speed tables (long flat top humps)
• Junctions plateaus (raised at junctions)
• ‘H’ humps
• ‘S’ humps
• Sinusoidal humps (may be round or flat top)
• Thumps
• Mechanical humps

These measures all consist of a physical raising of the carriageway surface to cause a vertical deflection (or change of level) for passing vehicles. Each type of hump has different qualities, benefits and dis-benefits, so the choice of traffic calming features and its actual design must be made carefully.

Round Top Humps

These are a low cost highly effective method of speed control. Historically, the ‘round top’ hump has been the most widely used form of road hump and is generally more effective in reducing speeds than various other means that have been tried. However, it has the disadvantage of causing discomfort to vehicle occupants as well as potential noise disturbance to nearby residents.

Road top humps can produce serious noise and vibrations problems caused by passing HGVs and are more suitable for residential roads with new HGVs, buses and emergency services vehicles. However, in recent years the unpopularity of road humps has led to the increasing use of other type of calming devices.

Flat top humps are often used in streets where there is a high frequency of conflicting movements between vulnerable road users and motorised vehicles, such as in residential and shopping areas. They are very effective at providing smooth and easy crossing places for pedestrians. Combined with the provision of central islands, this can change the overall look of an area to being much more pedestrians friendly and less like a main route for vehicle use only.

‘H’ and ‘S’ shaped, flat top humps are a variation of flat top humps designed to reduce the physical impact on buses and emergency services, while remaining effective in controlling the speeds of smaller vehicles.

Flat Top Humps/Speed Tables

The use of ‘flat top’ humps has a less severe impact on traffic than round up humps but will enable pedestrians to cross the road more easily. There are a number of different profiles in use, and each will affect traffic speed in different ways, depending on the height, shape and length of the hump as well as the speed characteristics of the road. The flat top road hump creates a surface that is level with the footway and can incorporate a zebra or signal controlled crossing, as well as constraining vehicle speed at that point. Care should be taken when constructing kerb to kerb flat top humps to ensure they do not exceed the maximum regulated height of 100mm.

Speed Cushions

The speed cushion was initially developed to enable vehicles with a wider track width (such as emergency service and public service vehicles) to traverse it with less vertical deflection than narrower private cars. A speed cushion is essentially a short, narrow, flat top hump that has to be replicated across the full width of the road, to prevent drivers taking dangerous avoiding actions by travelling on the opposite sides of the carriageway into on-coming traffic.

The size and shape of speed cushion needs to take account of the target traffic speed. The layout of cushion is also crucial, particularly where there is on-street parking.

On routes used by emergency services it is advisable to use cushions no wider than 1600mm. The height should be no greater than 75m and width between cushions or cushion to kerb should not generally exceed 1000m with 120mm as the maximum and 750mm as the minimum. The longitudinal spacing between sets of cushions should normally be 75mm maximum, less in 20mph zone/area.

Cushion can be invisible to pedestrians crossing the road and cause them to trip, so it is useful to mark them with white thermoplastic edge markings.

Road Narrowing, Footway Buildouts and Chicanes

Reducing the available road space for drivers by constructing road narrowing features alters the appearance of the streets and has the effect of lowering the speed at which drivers feel safe to drive. Road narrowing is form of horizontal traffic calming, as distinct from the vertical traffic calming.

The reallocation of street space can improve the quality of life of residents and reduce the dominance of motor vehicles.

Carriageway narrowing can take the form of:

• A gateway feature which retains two-way flow of traffic.
• A pinch point where traffic can only pass through the feature in one direction at a time (known as priority one-way working).
• Central islands to prevent overtaking
• Chicanes to force traffic to deviate from straight through path
• Reduced width over a length of road (while still being suitable for two say HGV traffic)
• Reduced width over a length of road within the use of advisory cycle lanes to visually narrow the street.
• Reduced width over a length of road such that light vehicles can pass each other but larger vehicle have to give way.

A combination of one or more of the above features can be used and overrun areas can also be provided to allow longer vehicles to pass whilst retaining the visual effect of a narrow street.

The above mentioned measures can be used to address specific local traffic issues and can significantly influence driver behaviour and traffic dynamics to create safer, more livable streets.

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