Speed breakers are safety devices that keep check on the fast-moving traffic. But
what does the speed breaker do when the vehicle is already slow approaching.
Is there any better breaking system design approach which keeps the fast-moving vehicles in check but
eases the travel of the slow-moving vehicles? 
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$\begingroup$ It is already easy for slow moving vehicles... What else do you really want? And note, that in some places it is there to cover a change in level between two surfaces not always to force a decrease in speed. $\endgroup$– Solar MikeAug 22, 2020 at 14:05
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1$\begingroup$ @SolarMike, I want it to completely disappear if I'm below the speed limit. See my answer regarding non-Newtonian fluid speed bumps. $\endgroup$– TransistorAug 24, 2020 at 22:10
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$\begingroup$ Sarcastic comment, but a police officers with radar guns or photo-radar? Speed humps, narrowing of the road are other common methods. $\endgroup$– Forward EdSep 3, 2020 at 19:04
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4 Answers
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Shallow, wide speed bumps are easy fore slow traffic while offering more or less the same impact as narrow, high speed bumps. Because the impulse force remains the same for fast speed.
They are having an unintended benefit: because of change in the subtended angle from the driver's eye to the bumper, they signal the distance better by changing the perspective as the approaching car get closer.
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$\begingroup$ I could be wrong, but I believe you are talking about what I understand to be the difference between a speed bump and a speed hump. A speed bump you can actually hit at speed and your suspension system will deal with it for the most part as its so short. A speed hump its probably 1.5-2 m wide, so if you hit it at speed your suspension can't absorb it. $\endgroup$ Sep 3, 2020 at 19:01
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Several companies have developed speed bumps / speed breakers that "disappear" when driven over below a set speed. My favourite designs are those that use non-Newtonian fluids. See this random paper for example.
As far as I can remember you can make a non-Newtonian fluid using water and lots of corn starch. Poke your finger in slowly and it will feel little resistance. Poke quickly and the fluid will "lock up". A search on YouTube should find plenty of examples. Practical designs will have to work over a wide range of temperatures and survive abuse by heavy vehicles running at high speed. They won't be using corn starch!
answered Aug 23, 2020 at 22:14
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$\begingroup$ So woud that be a rheoectic or thixotropic fluid? Both are non-newtonian. $\endgroup$ Aug 25, 2020 at 4:04
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$\begingroup$ I'm guessing several companies have developed things that flat out own't sell well because they'd cost a lot more than concrete and require a ton more maintenance. If you have that much cash, build the road right in the first place. $\endgroup$ Aug 26, 2020 at 9:16
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A common approach in residential areas where I live is to occasionally move a lane a car width towards the edge of the road every few thousand feet then back, with a small median and curb between the lanes. Essentially creating a slalom run. Probably not ideal in congested urban areas as it uses 1.5 times the space for the road but useful in suburban/rural housing developments where there is excess land. No problem navigating the turns at 35 mph but almost impossible at 80 (for cars at least).
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What you are talking about is called traffic easing or calming. The best solutions include the design of the road and everything around it. We build big wide roads and are somehow surprised that people drive fast on them. Speed bumps are a part of a solution when we can't get the other elements right. There are several types, and the uses are dependent on what we're trying to achieve exactly.
