It was a scene straight from the center of hell complete with burning wreckage, sprawling dead bodies-may their souls rest in peace and a smoldering inferno. It was a horrific crash that involved 12 vehicles, 11 of which were reduced to ashes. The death toll has hit 42. The crash on Saturday 10 December 2016 in the night resulted in an explosion at Karai near Naivasha. Media reports indicate that it all started when a truck, whose driver lost control after hitting a bump, crashed into vehicles heading towards Nairobi. The Uganda registered track is said to have been carrying highly flammable, nay highly explosive material. According to one account, the truck was carrying adhesives, whose contents included “toluene, alkyl phenolic resin, magnesium oxide, plinox TDX and chloroform,” chemicals which are highly flammable.

At the center of this tragedy lies a speed bump, hitherto placed there to save lives; the story of bumps in Kenya is a mixture of faux pas and design by déjà vu. The zeal and reactionary nature of the road agencies when it comes to installing and scrapping away speed bumps only demonstrates how chaotic highway design is carried out in Kenya. On one side the speed bump made a canter driver lose control having a dangerous cargo aboard while on the other side the bump made traffic on the highway slow down resulting in a line of sitting ducks. 

While government bureaucrats are still debating whether the presence of the bumps on the highway might have caused the accident, it is obvious they played a crucial role. The bumps were raised in February 2016 said the Principal Secretary for transport Irungu Nyakera. He says this is after the locals demanded for them. This was done by the government even after the Cabinet Secretary in charge of Transport said the government was set to remove speed bumps from major highways following complaints and even a court filing by the Nairobi Senator Mike Sonko.  The Senator had gone to court to ask for the removal of bumps on Thika superhighway and the incorporation of flyovers for pedestrians. The speed bumps have proven to be fatal, an avenue for traffic jams and a motoring nuisance.

Besides all these complains around fatal speed bumps, rumble strips and poor signage the road agencies seem hell-bent on  suffering these lethal designs upon the Kenyan motorist and other road users. Reports indicate that the bumps at Raini, where the Saturday carnage happened have proven to be devastating, being responsible for weekly accidents. It is common place to find broken glasses, pieces of automotive plastic and other motor vehicle parts close to these speed bumps on Kenyan highways.   While speed bumps are supposed to be used to calm traffic they have proved to be quite deadly.  

Speed bumps, speed humps and Speed tables are among the many types of traffic calming measures that engineers can employ. Speed bumps are applications, usually asphalt, that are from two to six inches high and one to three feet from front to back. Speed humps are usually less than four inches high but 10 to 12 feet from front to back. A Speed table, which is about the same height as a speed hump is considerably longer to accommodate a long flat surface and sloping ramps from street level to the table. A typical length for a speed table would be about 22 feet from front to back. All these and their aberrations can be found on Kenyan highways. 

These types of traffic calming measures are designed for relatively low speed roads, speeds typically expected in town centers or residential areas and not national highways. The maximum comfortable speed for crossing a speed bump is about five miles per hour so they are usually only appropriate for parking lots, private roads, and some low speed residential streets. Speed humps on the other hand are used on residential streets where speed limits do not exceed 25 miles per hour while Speed tables are appropriate for roads with slightly higher travel speeds.

Speed tables are essentially flat-topped speed humps, and may have a textured material on the flat section with asphalt or concrete for the approaches. They are sometimes called “trapezoidal humps” or “speed platforms”. If marked as a pedestrian crossing, speed tables may also be referred to as “raised crosswalks” or “raised crossings”. Speed tables are of a height of 3 to 3.5 inches and a travel length of 22 feet. Speed tables generally consist of 10 foot plateau with 6 foot approaches on either side that can be straight, parabolic or sinusoidal in profile. They result in speeds of 40 to 48 km/h. Speed tables are generally used on residential collectors, emergency routes or transit routes.

While standards may exist for these speed control measures, the Kenyan motorist experiences these measures in all kinds of shapes, sizes and composition. The reasons that trigger their erection is almost as diverse as the shapes they take.  Their appearance and disappearance on the road to the road user is almost as surprising as the rationale for their erection.  While speed bumps, speed humps and Speed tables are of questionable application at best in highways, in Kenya they seem ubiquitous. 

The decision to install these speed control measures includes consideration of the posted speed limit and the operating speed of traffic. They are recommended only on streets where the speed limit is 50 km/h or less. They are generally not considered appropriate where the 85th percentile speed is 70 km/h or more like in the highways. The Spacing and location of this speed calming measures and the length of the road segment where they are installed affect operating speeds on the affected roads. Traffic operation elements to consider include speeds, volumes and mix, emergency vehicle access, transit routes, vehicle and cargo damage, and environmental impacts. 

While the debate rages on about the killer bumps, we have not even started on “how to transport highly flammable cargo”. Is it possible however, for the government and its road agencies to be liable for the harm they cause through questionable designs?

Media report that speed humps:

  • Are expensive to install and expensive to maintain—Speed humps can cost $4,500 to $7,500. [Source: The Washington PostSept. 9, 2008]
  • Interfere with response times of emergency vehicles—Each speed hump costs fire trucks ten seconds in response time. [Source: ABC Orlando/WFTV, Jan. 28, 2010; and Fire Capt. Jeffrey Martin, St. Petersburg Times, Feb. 2, 2008; and the Tampa Tribune, Sept. 20, 2008]
  • Reduce property values—Prospective homebuyers reject home sites near speed humps. [Source: Tampa Bay Online, Sept. 30, 2009]
  • Increase noise levels—Speed humps usher in a constant barrage of scraping cars and engines revving over the humps. [Source: Tampa Bay Online, Aug. 12, 2009] 
  • Increase wear and tear on residential and commercial vehicles—Speed humps are a source of excessive wear on tires, brakes, suspension systems, shock absorbers and rattle dashboards. [Source: The Natchez Democrat, Oct. 28, 2009] 
  • Expensive to remove—Municipalities, under pressure by citizens and enforced by the courts, have been forced to remove speed humps at great expense to tax payers. [Source: Tampa Bay Online, Sept. 30, 2009]
  • Increase air pollution—On roads with speed humps, carbon monoxide emissions increase by 82 percent, carbon dioxide emissions double and nitrogen oxide increases by 37 percent. [Source:, April 22, 2009] 
  • Reduce fuel efficiency and increase gas consumption—By forcing drivers to brake and accelerate repeatedly, speed humps will cause a car that normally that gets 58.15 mpg travelling at a steady 30mph to deliver only 30.85 mpg. [Source:, April 22, 2009]




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