Sometimes, a "slow traffic" sign or low posted speed limit only does so much to slow down traffic — it's easy for drivers to ignore or miss these types of signs altogether. Unfortunately, they're posted for a reason: usually because there's a risk of harm associated with higher speeds, such as in a school zone, parking structure or construction area, where there's very little time to react.
In these types of situations, it's a good idea to also have a physical alert system on the road to let drivers know they need to reduce their speed. Speed bumps, speed humps, speed tables and rumble strips are all an ideal way to get the attention of drivers and alert them to a reduced speed. Each option has its own purpose and benefits once applied. Take a look at what sets them apart and when each should be used to help alert drivers, to keep speeds low.
Speed bumps are the most commonly recognized of all speed-reduction pavement installations. These abrupt sections of interference (bumps) on the road are typically used in environments where space is limited—such as a parking structure or a parking lot—to quickly take speeds down to about 2mph to 5mph.
The average speed bump is raised about 2" to 3" in contrast to the surrounding pavement and usually doesn't exceed 12" in width, to create an abrupt disturbance for drivers who might be travelling a bit fast. The bottom line is that a speed bump is impossible to ignore, especially at higher speeds.
Speed bumps are usually used to reinforce very low speed zones and are often prevalent in enclosed areas, such as parking structures. Because they help to keep speeds so low, they're great for improving pedestrian safety, reinforcing stop signs and reducing auto accidents on private streets and driveways.
The drawback of speed bumps is that they tend to impede low-clearance automobiles, such as snow plows and emergency response vehicles.
Rather than abruptly jostling drivers like a speed bump will, speed humps are a more passive way to reduce traffic speeds. Speed humps are actually designed to encourage lower speeds naturally, thanks to the undulating pattern they create—they gradually rock a vehicle up and down, to reduce its speed to about 10mph to 20mph.
Speed humps are generally only raised about 1" to 3" higher than the regular pavement, but the average hump installation can stretch to widths from 24" to 42" wide, making it a much larger application as compared to a speed bump! The concept behind them is to slow speed throughout an entire area, rather than just encourage abrupt speed reductions at critical points.
Because they offer more of a finesse when it comes to lowering speed, you'll commonly find speed humps used in areas where speed needs to be continually controlled. School zones, hospital areas and industrial drives all frequently employ speed humps, which gently handle vehicles of all sizes and clearances, keeping speeds controlled without risking undercarriage damage or the prospect of an overturned vehicle.
For slowing speeds in highly trafficked pedestrian areas, speed tables offer a versatile solution. A slight incline causes a natural reduction in speed by raising the wheelbase of vehicles, while the length of a speed table and subsequent decline sustain speeds at the reduced rate after encountering the table. Generally, speed tables are used to reduce speeds slightly, while still keeping traffic flowing smoothly at 20mph to 30mph.
Also called speed cushions, speed tables have a gradual rise of about 3" or so, reaching lengths of 20" or more. Speed tables are perhaps the smoothest of all pavement speed reduction installations, but the most natural in creating speed reduction without relying on driver action—inertia does all the work!
What makes speed tables unique are the many ways they can be configured. Because they're modular in design and don’t always span the width of the entire road, they can be placed in different intervals away from each other. Placing three or four cushions creates bypass sections for emergency vehicles, while the natural flow of traffic is still slowed.
Temporary Rumble Strips
Often confused with speed bumps because of their appearance on the road, temporary rumble strips are actually more of an alert system than a speed reduction system. As the name implies, rumble strips are placed on the road in short patches, which create an audible rumbling noise and quick rattle of the vehicle to immediately alert drivers.
Rumble strips usually only measure about 1" to 2" higher than the pavement around them, but can come in a variety of lengths depending on the installation. For example, rumble strips used to denote veering between highway lanes are usually only 5" to 7" long, while those being used as a shoulder alert system can be as long as 16", while on-road strips used to denote slowing speeds can reach 45" in length.
Typically, you’ll find temporary rumble strips in areas of higher speeds—usually 45mph and above—where the need to reinforce sudden speed changes or dangerous road conditions is important. Rumble strips can also be used to warn drivers of upcoming features, such as toll booths, road construction or access roads.
Slowing traffic the right way
As you can see, each type of speed reduction installation has its own way of reducing automobile speeds and is designed to maximize the effectiveness of speed signs or caution markers. Depending on the desired speed reduction, the area of installation and the intended purpose of each, it’s important to know which is best for the job: speed bumps, speed humps or speed tables.