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.”

 

 

3 thoughts on “Reader suggests new approach to building speed humps

  1. I am pretty sure that the speed bumps on Tracyton Highway in Silverdale are taller than 3 inches. More like 6-9 inches. And with the exception of the one closest to the red light that is pretty smooth going over, the other three are enough to knock you around a little bit. I mean you have to go over those things going less than 10 mph, or it makes your vehicle jolt and/or bounce around. Another thing about those speed bumps is why are they there on a road that is 30 or 35 mph and why so many. On foggy nights, if you dont know they are there, they will creep up on you. Another thing about those bumps is it can create a backup like nothing else. Even worse with the construction going on. But those cars that think they are race cars and have to have them so low to the ground usually go Bucklin Hill, but if one gets lost and ends up on Tracyton, will sometimes just stop in the middle of the road and try to make an illegal u-turn because they can go over them. And then here comes more back up. I still think that the hard plastic bumps that are just nailed into the asphalt should be put in all the neighborhoods where kids walk to school. They are pretty cheap and easy to install. Idiots fly through the neighborhoods to avoid lights and stop signs drive so fast by my house and it is going to take a kid getting hit by one of these idiots before the county or city decides that they are needed. By then its to late.

    1. I think if Dr. Iverson is getting knocked around by the speed humps so much that it hurts his neck, he needs to slow down. Less speed will equal less jolt.

  2. Have you ever been contacted for approval of the installation of any of the sites where they are installed? I haven’t, and I have lived here for 42 years.

    Somewhere I think I heard that it is the approval of 70% of the “Homeowners” along the “affected section” of road that is required.

    In my opinion, what is needed is speed cameras and quad times fine rates. The raise in fines could pay for the speed cameras, and let law abiding citizens travel the roads more safely and comfortably.

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