A “speed bump” is to slow a vehicle’s speed, not give give a “bump” to increase a vehicle’s speed. A joke was printed in Viz Magazine (UK) in 1999:
 
“These so-called speed humps are a joke. If anything they slow you down.
Tim Wakefield
Surrey”
 
The joke is often told with the term “speed bumps” instead of “speed humps.”
 
         
Wikipedia: Speed bump
Speed bumps (or speed breakers) are the common name for a family of traffic calming devices that use vertical deflection to slow motor-vehicle traffic in order to improve safety conditions. Variations include the speed hump, speed cushion, and speed table.
 
The use of vertical deflection devices is widespread around the world, and they are most commonly found to enforce a low speed limit, under 40 km/h (25 mph) or lower.
         
Google Groups: alt.sports.soccer.everton
OT….....and a fact for sure…...
GQ
12/3/01
Whilst we’re on the subject of road safety…......
......I’d just like to tell the government that these ‘so called’ speed humps are a joke!
 
If anything, they slow you down!
 
Quaggers!
     
Amazon.com
Viz Letterbocks - The Bulging Sack Hardcover – September 19, 2003
by Viz (Author)
With the possible exception of St Paul the Apostle’s epistles to the Corinthians, the funniest letters in the world appear on Viz Comic’s Letterbocks page. ‘These so-called speed humps are a joke. If anything they slow you down.’ Tim Wakefield, Surrey
 
Google Books
Dim Wit:
The Funniest, Stupidest Things Ever Said
By Rosemarie Jarski  
New York, NY: Random House
2008
Pg. 408:
These so-called speed humps are a joke. If anything they slow you down.
Tim Wakefield, Viz
 
Google Groups: smegjokes
Fw: pearls of wisdom
James
6/16/08
(...)
These so-called speed bumps are a joke. If anything, they slow you down.
Tim Wakefield,  Surrey .
 
31 December 2008, The Star (Johannesburg, South Africa), “Some famous last words lost in translation,” pg. 10:
Speed bumps are a joke. If anything, they slow you down.
 
Twitter
Chesney Hawkes
@ChesneyHawkes
these so-called speed bumps are a joke. If anything, they slow you down
12:30 PM - 10 Mar 2009
   
Twitter
Bernard R McMahon
@brmbds
I thought this a tad amusing: “These so-called speed bumps are a joke. If anything, they slow you down “
8:49 AM - 19 Mar 2009
     
Twitter
Alex Wakefield
@Inspec71
(The joke by Tim Wakefield is shown.—ed.)
Replying to @vizcomic
“@vizcomic: Tim Wakefield of Surrey opens this afternoon’s debate. ” >> my brother wrote this one, circa 1999.
9:58 AM - 9 May 2014
 
Viz Magazine (UK)
THESE SO-CALLED SPEED HUMPS ARE A JOKE
September 26, 2014     Letterbocks
These so-called speed humps are a joke. If anything they slow you down.
Tim Wakefield
Surrey
 
Twitter
John
@JFD1960
Those so called speed bumps are a joke. If anything they slow traffic right down
4:36 PM - 26 Apr 2018