What's the Difference Between Speed Bumps and Speed Humps?

When you are managing a busy school, a commercial warehouse, or a retail car park, the safety of every person on-site rests on how well you control vehicle movements. We often hear property managers use the phrase speed bump as a catch-all for any bit of raised asphalt or rubber on the road. However, choosing the wrong profile for your specific environment creates unnecessary frustration for drivers and, more importantly, can fail to provide the safety outcomes you need. Getting this decision right is a safety-critical task. Research cited in the NZTA Traffic Calming toolkit shows that introducing 20 mph zones, which is roughly 32 km/h, led to a 42 percent reduction in road casualties. The most significant drop was seen in serious injuries and deaths among younger children. This demonstrates that traffic calming is about far more than just slowing down a car: it is about protecting the most vulnerable people in our communities.

The primary difference between these two tools lies in their dimensions and the way they affect a vehicle. A speed hump is a gentler transition. According to the FHWA Traffic Calming ePrimer, a speed hump is typically 3 to 4 inches high, which is about 75mm to 100mm, and stretches across a length of 12 feet, or roughly 3.7 metres. Because of this longer, flatter profile, a speed hump creates a gentle rocking sensation. It is designed to slow traffic to a range of 15 to 25 km/h without forcing a complete stop. This makes them the preferred choice for local streets and connector roads where you want to maintain a steady flow of traffic while keeping speeds at a safe, moderate level.

A speed bump is a much more aggressive traffic calming device. These are shorter in length, usually between 30cm and 60cm, but can be up to 150mm high. When a driver hits a speed bump at anything over a crawl, the jolt is significant. This design encourages drivers to reduce their speed to between 2 and 10 km/h. Because of this intensity, we recommend speed bumps almost exclusively for internal car parks, driveways, and areas directly in front of warehouse loading docks. Using them on a public road or a high-volume access way often leads to vehicle damage and frustrated motorists who may try to swerve around them.

Vertical deflection is a technical term for any traffic calming measure that uses a change in height to influence driver behaviour. This includes humps, bumps, cushions, and tables. The evidence supporting these installations is clear. The FHWA analysis of vertical speed control devices found that field studies of 51 speed humps measured crash reductions between 33 percent and 48 percent. Furthermore, studies of nearly 200 speed humps showed a reduction in the 85th-percentile speed by 6 to 13 mph. The 85th-percentile speed is an engineering metric representing the speed at or below which 85 percent of vehicles travel. Reducing this number is a primary goal for any safety-conscious site manager.

In New Zealand, we look at safety through the lens of survivability. A Swedish study highlighted by the NZ Transport Agency notes that the risk of a pedestrian being killed when hit by a car at 50 km/h is five times higher than at 30 km/h. By installing the correct speed hump or bump, you are physically enforcing a speed limit that keeps these risks low. We have seen this work effectively in school zones where the presence of a well-placed hump ensures that drivers remain alert and slow enough to react to a child stepping into the road.

Traffic calming is often viewed as a way to restrict cars, but the broader benefits include improved foot traffic and commercial performance. A great example of this is the Auckland Fort Street shared-space project. After traffic-calming measures were introduced, vehicle speeds dropped by more than 25 percent and vehicle volumes decreased by over 30 percent. Crucially, peak-hour foot traffic increased by 50 percent. When people feel safe, they are more likely to walk, linger, and visit businesses.

For a business owner, this means that a well-designed car park is not just a place to leave a vehicle: it is the handshake of your business. If your car park is chaotic, fast, or dangerous, it reflects poorly on your brand. We often see property owners make the mistake of installing ad-hoc safety measures that do not comply with New Zealand standards. For instance, AS/NZS 2890.1:2004 provides specific requirements for off-street parking, including bay sizes and aisle widths. Integrating physical aids like speed humps and wheel stops as part of a compliant layout ensures that your site is both safe and legally sound.

Once you have decided between a hump and a bump, the next question is usually about materials. Most modern installations use either heavy-duty rubber or asphalt. Rubber speed humps and bumps are highly popular because they are durable and offer a tidy, professional finish. They are often modular, meaning they are easy to install and can be adjusted or moved if your site layout changes. We find that rubber is excellent for car parks and private roads because the sections are pre-coloured in high-visibility yellow and black, which reduces the need for constant repainting.

Before you commit to an installation, there are a few practicalities to consider. First, think about the types of vehicles using your road. If you have frequent heavy truck traffic, you may need a wider speed cushion rather than a full-width hump to allow emergency vehicles or large trucks to pass with less impact. Second, consider drainage. A speed bump that spans the entire width of a driveway can act as a dam during a heavy North Island downpour, leading to puddles and slip hazards. We always look for these potential issues during our initial consultation to ensure the road surface remains safe in all weather conditions.

Finally, remember that a speed bump is only effective if drivers can see it. Clear marking and signage are essential. A sudden, unmarked bump is a hazard, not a safety feature. By combining professional installation with high-visibility marking, you protect the vehicle occupant and your own liability. If you are unsure which traffic calming device is right for your property, we are here to help. Our team has over 50 years of combined experience in traffic management solutions, and we pride ourselves on providing straight-up advice that helps you decide on the best course of action for your site.

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