theres a big highway going to my hometown. Its a toll road so you pay a toll whenever you use it. Its long and well maintained. Traffic averages 100kmh. Before it was renovated, I noticed that the toll booth was built on a hill 2-3 meters high with a shallow grade.

So i'm going 100kph, I approach the toll booth to pay the toll. I use the brakes but my car also goes uphill so some of my kinetic energy is converted into gravitic potential energy. As i leave, I hit the gas pedal, but I'm also going downhill so gravity assists me in accelerating.

I probably saved a miniscule amount of fuel. But a couple of hundred thousand vehicles use that highway every day so, I wonder if the total amount of fuel saved is significant. It would be useless if the line of cars waiting to pay extends down to the base of the hill.
-- vmaldia, Aug 09 2006

Elevated stop lights elevated_20stop_20lights
Similar. [spidermother, Aug 09 2006]

Correct gravity is a conservative field.
-- madness, Aug 09 2006


[madness], darling, do you realize how little sense you make? Wot the blazes is "correct gravity"? Or did you mean "Correct: gravity is a conservative field?" And what does that mean, anyway? Are you alluding to the principle of conservation of energy? Or conservation of momentum? Or what?
-- moomintroll, Aug 09 2006


A lawyer once told me punctuation should be ignored --- so I stopped using it. Lawyers are always right...

Wow ummm. I pick.... Energy! Anyway Correct gravity is conservative.
-- madness, Aug 09 2006


Well, yes it would work [+], particularly at road tolls. It's a little bit baked, as you observe yourelf.

It's also been applied to rail systems - London Underground's Jubilee Line has gradients up to and down from each platform for exactly this reason.

It's probably more applicable to the rail environment, because speed and braking rates are more predictable and consistent, and you don't (usually) get queues of trains waiting at the bottom of the gradient.
-- Frankx, Aug 09 2006


So, um, isn't this a "me too" or a "let's all" ?
-- DrCurry, Aug 09 2006


Actually Doc this sounds more like a "isnt it cool that thing I saw" but certianly not an idea.
-- jhomrighaus, Aug 09 2006



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