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Car Forum / Driving, Maintenance, Tuning / Driving / December 2005Filling the gap
I want to pose a hypothetical question here: You are traveling along an Interstate highway on which one of the two lanes in your direction of travel is closed for construction. Traffic is slogging along at about 25 MPH. Miraculously, the next 17 vehicles ahead of you all exit at the same offramp, leaving a huge gap ahead of you before the next car doing 25 MPH. My question to you is: At what speed do you close the gap? The regular posted limit is 65, the construction posted limit is 45, and if the road were empty you'd be doing 75. By the design of this hypothetical situation, what you do does not affect your arrival at your destination, as long as you increase your speed beyond 25. You will still catch up to the next car (the one that was 18 cars ahead of you) before the next offramp (which you know is 5 miles ahead). No one will pass you (remember, the other lane is closed), and you will not pass anyone else. Of course, please give your reasons for your answer; I'll post my answer in a day or two. >By the design of this hypothetical situation, what you do does not affect >your arrival at your destination Of course it does. Not by much, but it does. >You will still catch up to the next car (the one that was 18 cars ahead >of you) before the next offramp (which you know is 5 miles ahead). No one [quoted text clipped - 3 lines] >Of course, please give your reasons for your answer; I'll post my answer in >a day or two. Why, I would maximize the area under the acceleration curve, of course. The higher my velocity, the lower my travel time. Scott en Aztlán wrote: <brevity snip> > Why, I would maximize the area under the acceleration curve, of > course. The higher my velocity, the lower my travel time. ----- Bizarre perspective... or you simply didn't understand the situation as presented. Higher velocity rarely means shorter travel time in a wheeled vehicle in typical day-to-day travel. I think most people are fooled into feeling as if they've arrived sooner because they've experienced higher velocities... but those time savings are usually negligible or imaginary. ----- - gpsman >Higher velocity rarely means shorter travel time in a wheeled vehicle >in typical day-to-day travel. That is of course false. Travel time is inversely proportional to velocity, given a trip of the same distance. >I think most people are fooled into >feeling as if they've arrived sooner because they've experienced higher >velocities... but those time savings are usually negligible or >imaginary. They are small in day to day travel, because total time is small. Small, however, does not mean negligible.  SignatureThere's no such thing as a free lunch, but certain accounting practices can result in a fully-depreciated one. > My question to you is: At what speed do you close the gap? Take the speed up smoothly (not above 45) until half the "slack" is covered, then an inverse smooth ramp down to the traffic speed as you close the gap. This saves fuels and reduces the "shock" of the traffic chain (the huge acceleration / decelaration spurts). > Take the speed up smoothly (not above 45) until half the "slack" is covered, > then an inverse smooth ramp down to the traffic speed as you close the gap. > This saves fuels and reduces the "shock" of the traffic chain (the huge > acceleration / decelaration spurts). > ----- Why close the gap at all?!? Forget about closing the space between yourself and the vehicle in front of you as a method of speeding your travel! What, you're going to arrive sooner because the vehicles at the next on-ramp won't be merging in front of you...?! The situation states: "By the design of this hypothetical situation, what you do does not affect your arrival at your destination, as long as you increase your speed beyond 25.". This is a great demonstration of a lack of *thinking* about driving... even when you're just thinking about driving. ----- - gpsman >> Take the speed up smoothly (not above 45) until half the "slack" is >> covered, then an inverse smooth ramp down to the traffic speed as [quoted text clipped - 3 lines] > > Why close the gap at all?!? For the simple fact that closing the gap is a more efficient use of the roadway. <<JohnH wrote... Take the speed up smoothly (not above 45) until half the "slack" is covered, then an inverse smooth ramp down to the traffic speed as you close the gap. This saves fuels and reduces the "shock" of the traffic chain (the huge acceleration / decelaration spurts). >> What he said. It takes up the slack within established speed limits (no ticket and minimized crash hazard), reduces the possibility of some impatient moron seeing that huge gap in front of you and trying to pass you via a shoulder or the two inches of bare space by the construction zone, and provides the least likely risk of getting hit from behind when you drop from 45 to 25 in a short distance. > <<JohnH wrote... > [quoted text clipped - 13 lines] > when you drop from 45 to 25 in a short distance. >----- -- > "By the design of this hypothetical situation, what you do does not affect your arrival at your destination, as long as you increase your speed beyond 25." < -- What *that* means is: No impatient drivers and no increased risk of being rear-ended. You are not free to inject your own suppositions. Even without that criteria your rationale is flawed. How many times have you been passed via the shoulder? Probably zero but even if it's ten, you probably didn't collide. That point is moot. Why would you decelerate from 45 to 25 "in a short distance"? We're talking about a gap of 18 car-lengths here, somewhere in the neighborhood of 150 yards. You'd accelerate from 25 to 45 to close that gap...? My way of thinking would be that that would not only make you more susceptible to being rear-ended... but also more likely to rear-end the vehicle in front of you *and* increase the velocity at which either event might occur. ----- - gpsman >> My question to you is: At what speed do you close the gap? > > Take the speed up smoothly (not above 45) until half the "slack" is > covered, then an inverse smooth ramp down to the traffic speed as you > close the gap. This saves fuels and reduces the "shock" of the traffic > chain (the huge acceleration / decelaration spurts). I would take a similar approach (smooth acceleration/smooth deceleration) but only to 30 MPH. How long would it take me to close the gap? Let's imagine that I and the 17 now-departed cars were each maintaining a following distance of 2½ car lengths (at 25 MPH). The gap is about 60 car lengths, which is just under a quarter of a mile (assuming 20-foot car lengths). 17 * 3.5 = 59.5, which includes the 2½ car lengths plus the length of the departed cars themselves. At 25 MPH, the next car ahead of me would take 2:24 to cover 1 mile. At 30 MPH, my car would take 2:30 to cover 1¼ miles. So, within 1 mile of driving at 30 MPH, I would have filled the gap. >>> My question to you is: At what speed do you close the gap? >> [quoted text clipped - 17 lines] > 30 MPH, my car would take 2:30 to cover 1¼ miles. So, within 1 mile of > driving at 30 MPH, I would have filled the gap. I knew that this was an approximation, so I resorted to Algebra to see some answers:. 1¼ miles at 25 = 1½ miles at 30 = 3 minutes. I would have gained ¼ mile in 3 minutes at 30 MPH over a distance of 1½ miles while the car at the back of the pack ahead of me would have covered 1¼ miles. 1 mile at 25 = 1¼ miles at 31¼ = 2.4 minutes. I would have gained 1/4 mile in 2:24 minutes at 30 MPH over a distance of 1¼ miles while the car at the back of the pack ahead of me would have covered 1 mile. 5/16 mile at 25 = 9/16 mile at 45 = 3/4 minute. I would have gained ¼ mile in just 3/4 minute at 45 MPH over a distance of 9/16 mile while the car at the back of the pack ahead of me would have covered 5/16 mile. 5 miles at 25 = 5¼ miles at 26¼ = 12 minutes. I would have gained ¼ mile in 12 minutes at 26¼ MPH over a distance of 5¼ miles while the car at the back of the pack ahead of me would have covered 5 miles. It's interesting to see just how quickly the gap would have been filled at 45 MPH, and just how little it would have taken (just an extra 1¼ MPH) to cover the gap over 5 miles. > My question to you is: At what speed do you close the gap? Any particular location on this globe? My answer will vary depending upon the behavior of local drivers. If this is the chicago area, infested with a nasty combination of 'me first f.ck you' and sloth drivers I will drive as fast as I can such that I am able to avoid a collision. This might be 10mph, it might be 50mph. It will depend on details of the conditions and other drivers present. For instance, if it is snowing at a good pace, with snow on the road and there a good number of SUVs in the neighboring lane and no shoulder to escape to, I will drive 10mph or maybe less, simply trying to drive such that I will not need to come to a dead stop unless someone cuts me off and be able to do so should someone do that. If it's a bright summer day, the lane next to me goes somewhere other than where I'm going. (ie a split) and there is a shoulder for me to escape to, I'll probably do around 45mph. If it was on the autobahn in Germany, I would probably calmly proceed at the same rate I was going before the vehicles exited because the odds are overwhelming that if a driver moved in front of me he would be competent. I would not have a significant risk of some move of astounding stupidity, aggression, etc. I would not have to worry that the person moving in front of me was a sloth or enabler who make things worse for me. It wouldn't be a game of posisition on the autobahn while it would be on an interstate in chicago. > there a good number of SUVs in the neighboring lane and no shoulder to Did you even read the posting? >> there a good number of SUVs in the neighboring lane and no shoulder to > > Did you even read the posting? Yes, I thought he meant before the closure. On second reading maybe he means after it, in which case, why does it matter? The only thing one has to do is defend against shoulder passers if said shoulder exists. > The only thing one has to do is defend against shoulder passers if said shoulder exists. ----- How, exactly, do you "defend" against "shoulder passers"...? ----- - gpsman You drift over toward the shoulder, Duh. Bernard >> The only thing one has to do is defend against shoulder passers if said >> shoulder exists. [quoted text clipped - 3 lines] > > - gpsman |
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