Tag Archives: speed humps

Another idea to soften speed humps proposed

The in basket: Yet another reader has chimed in with yet another idea for making speed humps less harmful for cars and less painful for those with back problems.

Jim Matthews called to suggest leaving gaps maybe 10 inches wide  in the speed humps, too narrow to be sure of going through them if one’s speed is high, but wide enough for a driver to pass through at a slow speed without the jounce all our local speed humps provide.

I hypothesized that fear of accidents caused by loss of control from vehicles’ slipping sideways into the spaces, and the wide variety of wheel bases would make such an idea impractical, but I asked Kitsap County if its engineers had any thoughts on the subject.

The out basket: Turns out that Jim’s idea has actually been tried, according to County Traffic Engineer Jeff Shea.

“A device similar to what the reader is describing has been used in other jurisdictions,” Jeff said. “The device is not designed for the purpose of easing through the bump, but rather for emergency vehicles so they don’t have to slow down.

“The device has been referred to as a ‘Speed Pillow.’ They are not very popular and not widely used around here. They are difficult to build and even though they are designed for emergency vehicles, most cars can easily traverse through them without slowing down at all.  The ones I have driven over did not do a very good job of slowing me down.”

Reader suggests new approach to building speed humps

The in basket: Retired orthopedic surgeon Larry Iversen noted the recent Road Warrior column on the reason for speed humps and suggested a modification.

“I understand that the idea of speed humps is to discourage drivers from exceeding the speed limit,” he wrote, “but why punish those of us who drive the speed limit with a jolt that aggravates the pinched nerve in my neck, even when I am traveling the speed limit?

“There must be a civil engineer smart enough to design humps that are comfortable to cross at the posted legal speed, but will create an uncomfortable ‘jolt’ at higher speeds, such as 10 mph higher.”

The out basket: Jeff Shea, traffic engineer for Kitsap County, and Jerry Hauth, street engineer for Bremerton, replied to Larry’s suggestion,

“One of the biggest challenges with speed humps or tables is that all drivers, law abiding and not, must traverse these traffic control devices,” Jeff said. “Because of this, under our local streets traffic-calming program we require approval of 70 percent of the affected motorists before installing them. “The size and shape of the speed humps are designed to slow traffic well below the speed limit so speeds between the devices are close to the posted speed limit.  If the speed humps were designed for the posted speed, chances are we would still see the high speeds between them.

“Design of these devices is a tricky task,” he said.  “The first variable would be the motorist. Who would be the average driver or lowest common denominator for the design; a healthy young individual, or an older individual with back problems?

“The other variable would be the vehicle; many suspension systems are different with more or less tolerance for bumps than others.  Picking an average or less than average for the design would be a challenge to ensure the hump was traversable by most motorists, but not too traversable to allow too high of speeds.

“There are the three basic configurations; speed bumps, speed humps, and speed tables.  Speed bumps are very abrupt and normally found in parking lots. They are constructed to get motorists below 5 mph.  Speed humps, usually 3 inches high by about 12 feet long, are comfortably traversed by a majority of motorists at a speed of about 10 mph and tables, usually 3 inches high by 22 feet long, are designed for about 15 mph.

“Because of that, and for safety and liability concerns, Kitsap County constructs accepted industry-standard speed hump profiles.  County speed humps are built to Institute of Transportation Engineer’s standards.

“The county builds speed humps using asphalt.  So even though we try to meet ITE standards there is always some minor variance in the dimensions.  This is due to the forming and compaction characteristics of asphalt.  It is difficult to get exact dimensions with asphalt.”

Jerry said, “Most ( if not all) of the engineers that I have interacted with over the years have not been big advocates of speed humps for numerous reasons. You may want to ask emergency responders what they think about them.

“The initial speed bumps caused a radical bounce, which made them acceptable for a parking lot, where a vehicle should be going very slowly, but not on roads. The more recent introduction of speed humps and tables was intended for low volume, relatively flat roads, with the expectation of setting up a rocking effect in the vehicles that people find very unpleasant and be forced to slow down. However, the general effect typically is you almost need to crawl over them in order to not destroy your vehicle or your body.

“The answer to the doctor’s question is that sadly we civil engineers have not come up with a design for these that can effectively slow the vehicles down, without the dramatic impacts to both vehicle and occupant.”



Bone-jarring park speed bumps widened

The in basket: Peter Madsen writes, “We were at Anderson Point County Park August 13, and I think that the county really got carried away with the speed bumps they installed. They are higher and more abrupt than any I’ve seen elsewhere, and even at dead slow speed our 2009 Accord bottomed out on the one next to the park entrance. So far it isn’t dribbling oil all over the place….

“Isn’t there some sort of a standard for speed bumps?” he asked. “More and more, your replies in this column strongly imply that there’s some federal or state standard for everything with regard to traffic. I’d think that the normal speed bump should be navigable by the normal average sedan without fear of damage. But those speed bumps are too abrupt and too high.”

The out basket: Peter e-mailed later that day to say a Facebook post from someone else said the bumps had been smoothed, and by the time I got out there, four of the five were widened to a comfortable level. But the fifth one, the one closest to the parking lot, was bone jarring. It was as bad as some you will encounter in some mobile home parks or the ones that were briefly in place at South Park Village Shopping Center in South Kitsap a few years ago before, I assume, shopper protest got them lowered and/or widened.

Doug Bear of Kitsap County Public Works, which did the work for the parks department, said, “The original speed bumps installed were not viewed as being effective in slowing traffic. They were built up, then residents and park visitors felt they were too abrupt. So the bumps were lengthened to create 12 feet long speed humps which are in place now. These conform to the existing county standard.” The fifth one was to be smoothed that day, he said.

As for standards for installing them, Jeff Shea, the county’s traffic engineer says, “Traffic calming devices that cause vertical displacement are usually called either speed bumps, speed humps, or speed tables.  Speed bumps are generally small and generally very abrupt.  They are used in parking lots quite often.  They are designed to force a vehicle to nearly come to a stop to maneuver over them. Kitsap County doesn’t use these on public roads.

“Speed humps are less abrupt, but do require a significant speed reduction to go over them comfortably.  They are normally spaced to allow motorists to achieve the posted speed between the bumps while decelerating and accelerating.  Speed humps are used by the county on local streets.  Speed tables are even less abrupt and are used primarily on roads that have bus traffic and larger vehicles on them.” Tracyton Boulevard has speed tables.

“The Manual on Uniform Traffic Control Devices doesn’t spell out how to build nor does it give specifications for the shape of the device,” Jeff said.  “The MUTCD gives the signing and marking requirements if speed humps or tables are used.

“The MUTCD doesn’t require signs, but recommends them with an Advisory Speed sign below the warning sign.  If (pavement) markings are used, it specifies how those markings should look and be placed.

“There is no federal requirement on the dimensions of a speed hump or table. Kitsap County tries to get their speed humps to about 3 inches (tall).  The width of the speed hump is usually about 12 feet. The speed humps can be formed into several shapes.”

Getting the humps to look as planned is a challenge, he said.  “Kitsap County builds their speed humps from asphalt. It is extremely difficult to screed the hot material into one of the shapes and compaction of the asphalt will impact the actual final height of the speed hump. This explains why speed humps around the county can vary in their impact to motorists.

“We could build them closer to the specifications, but that would take concrete.  Concrete costs significantly more and requires a much longer cure period before traffic can drive on it.

“A speed table is simply a speed hump with a flat top,” he said.  “The flat area is normally about 10 feet long.  The flat top makes if a little more comfortable for long wheelbase vehicles to maneuver over the device.  It also allows passenger vehicles to traverse a little faster than over a speed hump.”

I notice that the county’s signs warning of them call them ‘speed bumps’ and urge a 10 mile-per-hour speed to cross, though they really are speed humps. Bremerton’s signs say “speed humps” and urge 15 mph, though there’s not much difference in the two jurisdictions’ humps.