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Highway rest-stops and tollbooths share a common functional element which wastes energy: vehicles using the facilities decelerate from driving speed to a complete stop (,occupants do their thing,) then re-accelerate back to highway speed, wasting both brake-lining and gasoline in that order. Heavy trucks
impede the flow of traffic while they, of necessity pre-brake before the offramp, and again when they slo-o-o-wly accelerate while in the flow of traffic (a trait shared by underpowered passenger vehicles, also).
If we design and build the facilities at a higher elevation than the highway then we can use the approach ramp to decelerate the vehicles to "apron speed" then use the departure ramp to re-accelerate them back to driving speed without using appreciable gas or brakes. Level height is determined by the difference between the highway speed limit and the parking-lot/apron speed limit.
There is no downside to this: give or take aerodynamics, all vehicles will decelerate/accelerate at the same speed, Ferraris and Yugos and 18-wheelers alike. Initially higher construction costs would be very quickly made up for in gas and brake-lining savings to users and the environment.
elevated stop lights
elevated_20stop_20lights
sorry, I've linked to this same idea twice in as many days [xaviergisz, Feb 25 2009]
Highway Rolling Regenerative Service Station
Highway Rolling Reg...ive Service Station
Alternate take on the same idea using a 'rolling' concept where enregy is stored in motion, rather than storing potential energy via elevation. [zen_tom, Feb 26 2009]
and the version for highway intersections
Triple-Decker_20Highway_20Intersection
[FlyingToaster, Mar 11 2009]
[link]
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Might also be very pleasing to the eye: Every lane has a ramp fitted to the mean velocity of its occupants, so you get a light-through-a-prism look. |
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Can't argue with your logic, FT. Although I've seen exit ramps that are raised and correspondingly declining entry ramps, I've never seen it done at rest stops. The only problem with determining level height is that speed limits are subject to change, and level height of a rest stop is much more difficult and expensive to change accordingly when it does. (neutral) |
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There used to be an idea on the HB for a mass transit system consisting of a flat, high speed track, with local stations on a roller coaster system on a parallel track.
Trains released from the local stations would match speed with the express trains, passengers would transfer in either direction, and the local trains would then mount the hill at the next station. |
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I suspect that there would be an effect where impatient drivers put their foot to the floor on approach to get to the top of the hill faster and then brake. |
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Have you done the math on how much energy/carbon it will take to raise those facilities appropriately, and after how many car visits you can expect to break even? |
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If you didn't want to build a massive, unsightly hill you could build a version of this which slowed cars down by having them drive over massive inductance coils buried in the road on the approach to the toll-booths. The energy taken from your car on the approach would be stored in huge capacitors and given back to you as a massive speed boost via another set of inductance coils on the other side of the toll-booth. |
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Or something like the HotWheels rotating rollers thing.
Could use adapted car wash hardware. |
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[x] in your <link> traffic would be slowed in *all* directions at the same time, thus actually impeding the flow. |
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//The energy taken from your car on the approach would be stored in huge capacitors and given back to you as a massive speed boost via another set of inductance coils on the other side of the toll-booth.// |
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Only as long as the exits are through a tunnel with a light sequencer. |
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Doesn't the new breed of hybrid electric cars with regenerative braking make this a little pointless? |
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//hybrid electric//
regen braking can only recover/reuse maybe 80% of the energy; this is 100pct minus rolling resistance (which also slows down electric cars) |
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You see this a lot in Australia along the Hume. |
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I have a hard time persuading people that coasting isn't somehow dangerous, or a dark art of some sort. Even if you built such a system many drivers would still race up the ramp, slam on the brakes, and gun it back down the ramp on the other side. No savings to be had. |
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//race up the ramp//
signs for "optimum speed" interspersed... after a few rest-stops most drivers would pick up on it. |
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//coasting isn't somehow dangerous//
I think the problem is that most people consider coasting to be analgous to "engine off" where they lose all the power-control functions. A real stumbling block might be engine-braking by such people... still save on gas but not as much. |
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I liked the idea so much, my original annotation blossomed off into an idea of its own. |
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It's easy to stop drivers accelerating on the approach - provide a surface with a low friction in the forwards direction (good traction transversely makes sense for steering). If one accelerates, wheels spin, smoke is produced but otherwise there is little discernible benefit. |
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Alternatively, speed cameras would do the job quite well. Tickets for all those at over the speed obtained by someone entering the approach at the speed limit and then coasting. |
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[vvv] the only speed limit that's really important is the parking-lot speed (which is true in any case). Other than that I'd just go for an orange flash if you're a bit over the recommended, maybe a green flash if you're under: trucks would usually be under given their (lack of) aerodynamics while swoopy cars would be over... I haven't run the calculations yet on best approach/departure angles: there's probably a weather angle, too. |
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I just did the math and for a 70mph vehicle you need to build 48 meters high. That's quite high. |
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[BadJim] you sure of that ? I get going from 70mph to 15mph to be about 80ft'ish.. not including drag... so more like 20m. |
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If the cars were going fast enough, you could build a loop of road and have the toll-booth upside-down at the top of the loop. |
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It's way too similar to [WhiteWiz's] idea for me. I'm surprised that it's not been mfd'd yet. I don't like doing that, but it seems fairly redundant to me. Maybe I'm missing something? |
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[x] The only thing about [WW]'s idea that works is [bristolz]'s illustration (which is why I [+]'d it). I've added an anno over there that might help. |
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For a variation that replaces 4-way stoplights and cloverleafs on highways, see my "TripleDecker" post, but that one isn't meant to replace stoplights for urban usage. |
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70 mph = 112.65408 kmph = 31.2928 metres/sec |
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Energy= Mass * Velocity * Velocity / 2 |
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E/M = 31.2928 * 31.2928 = 489.61966592 |
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Energy = Mass * Gravity * Height |
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Height = E /( M * 10 ) = 48.961966592 metres |
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I used a different equation: you're right though; I get the same'ish answer... gives an indication of how much energy could be saved per vehicle, dunnit... haven't worked in aerodynamic drag and rolling resistance yet because I'm not sure of what angle(s) the ramp should be at: bit of vehicle and human ergonomics there. |
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if vehicle mass is 1000kg, |
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E = 1000kg X 9.8m/s^2 X 50m = 0.5MJ = 0.01L of gas = $0.01 value. |
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if vehicle mas is 20,000 kg, then it is $0.2 value. |
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Throw in an weighted average of $0.05 |
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What ever your cost estimate is in dollars can be multiplied by 20 for the number of stops required for payback. ie $1.0M = 20,000,000 stops. Over 50 years, you would need a car stopping every 1.5 minute. Oddly enough, it seems feasible for busy stops... wind and rolling resitance can possibly be cancelled out by my (false) assumption of perfectly efficient use of gasoline @ 35MJ/L... |
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I don't like the idea of these platforms in general, so I'm fishboning it in favour of efficient on-board regenerative brakes. |
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//wind and rolling resistance// are going to be there whether it's a flat ramp or an inclined one. |
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//platforms in general//
It's a hill (platform is my other post concerning 4-way highway intersection <link>) |
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//regenerative braking// should be on all cars, trucks, agreed but an inclined ramp allows all vehicles regardless of power:weight to merge at highway speed. Note that this also cuts down on the size of the regenerative capacitor you'd need in order to recover or assist 70mph delta-V's... I imagine most regen systems wouldn't be sized for more than a 40mph regeneration (weight issues). |
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I think I may have greatly underestimated the constuction cost. When I get a chance, I will calculate the approximate number of dump truck loads of dirt required. |
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[knowtion] sp. "bulldozer" or "crane": while not an architect I imagine your estimate low for a platform, but rather high for a hill (much more so if they're installed while the road is being built). I imagine there's a facility-size point where it becomes more economical to make a platform. |
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True enough about the bulldozer. I still think my cost is low if anything though... but I'm not a civil engineer either. |
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