# Driving time puzzle **URL:** \ **Category:** The Game Room\ **Created:** [December 16, 2011, 12:13pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403 "2011-12-16T12:13:40Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Corresponder](https://avatars.discourse-cdn.com/v4/letter/c/22d042/32.png) [@Corresponder](https://boards.straightdope.com/u/Corresponder)\ **Post date:** [December 16, 2011, 12:13pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/1 "2011-12-16T12:13:40Z")
You are driving along a straight highway. Your very accurate cruise control keeps you at exactly 60 mph. Your GPS device is programmed to take you along this route to point B. At point A it tells you you have exactly 60 miles to go. Similarly, you have measured the distance from A to B on a very accurate large-scale map and gotten exactly 60 miles. You start a very accurate stopwatch at point A. When you reach B, the stopwatch, instead of reading 1 hour, reads 1 hour and three seconds. How can this be? (I will eventually give my answer in this thread.) ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [December 16, 2011, 12:36pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/2 "2011-12-16T12:36:04Z")
Hills? ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [December 16, 2011, 12:41pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/3 "2011-12-16T12:41:44Z")
tire wear/pressure? ---
**Author:** ![Reebevoli](https://avatars.discourse-cdn.com/v4/letter/r/49beb7/32.png) [@Reebevoli](https://boards.straightdope.com/u/Reebevoli)\ **Post date:** [December 16, 2011, 12:45pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/4 "2011-12-16T12:45:57Z")
Curvature of the Earth? ---
**Author:** ![brittekland](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@brittekland](https://boards.straightdope.com/u/brittekland)\ **Post date:** [December 16, 2011, 12:47pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/5 "2011-12-16T12:47:06Z")
> [@Ximenean](#): > > Hills? I thought of ‘variable factors’ but “very accurate cruise control” would compensate for the various resistant forces, wouldn’t it? I was thinking it has something to do with Geographic Variations in Positioning Errors of satellite to GPS unit or something but 3 sec per 60 min/60 miles is a lot. ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [December 16, 2011, 12:53pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/6 "2011-12-16T12:53:42Z")
> [@brittekland](#): > > I thought of ‘variable factors’ but “very accurate cruise control” would compensate for the various resistant forces, wouldn’t it? > > I was thinking it has something to do with Geographic Variations in Positioning Errors of satellite to GPS unit or something but 3 sec per 60 min/60 miles is a lot. No, I mean going up and down slopes adds some distance. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [December 16, 2011, 12:59pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/7 "2011-12-16T12:59:30Z")
It’s those damned neutrinos again, isn’t it? ---
**Author:** ![brittekland](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@brittekland](https://boards.straightdope.com/u/brittekland)\ **Post date:** [December 16, 2011, 1:00pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/8 "2011-12-16T13:00:05Z")
> [@Ximenean](#): > > No, I mean going up and down slopes adds some distance. Agreed. > [@](#): > > It’s those damned neutrinos again, isn’t it? Or Higgs Boson… ---
**Author:** ![brittekland](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@brittekland](https://boards.straightdope.com/u/brittekland)\ **Post date:** [December 16, 2011, 1:07pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/9 "2011-12-16T13:07:35Z")
I assumed “a straight highway” as a level straight highway. ---
**Author:** ![sandra\_nz](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@sandra\_nz](https://boards.straightdope.com/u/sandra_nz)\ **Post date:** [December 16, 2011, 1:19pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/10 "2011-12-16T13:19:20Z")
The inability of a car to drive in a perfectly straight line? ---
**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\ **Post date:** [December 16, 2011, 1:44pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/11 "2011-12-16T13:44:25Z")
That extra three seconds is 264ft, or 88 yards, at 60 mph. What’s that tell us? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 16, 2011, 1:48pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/12 "2011-12-16T13:48:31Z")
> [@Corresponder](#): > > you have measured the distance from A to B on a very accurate large-scale map and gotten exactly 60 miles. If this map is one that, like most, renders the surface of the earth as a plane, then note that it can be fully accurate only in one dimension. ---
**Author:** ![Corresponder](https://avatars.discourse-cdn.com/v4/letter/c/22d042/32.png) [@Corresponder](https://boards.straightdope.com/u/Corresponder)\ **Post date:** [December 16, 2011, 1:49pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/13 "2011-12-16T13:49:35Z")
> [@Ximenean](#): > > Hills? Yes, this is the answer I intended. I didn’t think someone would get it so quickly. If the road is hilly, then you actually have to travel more than 60 miles. I noticed the other day that, even with my cruise control on, my GPS would display a slightly lower speed than my speedometer when I was going UP or DOWN a hill. Apparently the GPS only calculates your speed as if you were travelling on a flat terrain, in terms of latitude and longitude; the same is true with a flat map. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 16, 2011, 1:52pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/14 "2011-12-16T13:52:37Z")
> [@Reebevoli](#): > > Curvature of the Earth? Both maps and GPS receivers take this into account. So, for example, if you ask your GPS receiver to tell you the straight-line distance from NYC to LA, it gives the length of a great circle route across the surface of the earth, not the distance of a tunnel through the earth. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [December 16, 2011, 2:02pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/15 "2011-12-16T14:02:48Z")
That would be roughly an extra three miles of travel. In my old age my ability to solve pythagorean equations is letting me down, but I think those would be some significant hills. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 16, 2011, 2:08pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/16 "2011-12-16T14:08:50Z")
> [@jjimm](#): > > That would be roughly an extra three miles of travel. In my old age my ability to solve pythagorean equations is letting me down, but I think those would be some significant hills. Which “that” would be 3 extra miles? If you mean the OP’s problem, he said the clock ran 3 \*seconds \*long. At 60 mph, it’d take 3 \*minutes \*to chalk up 3 extra miles. Ref post #11 for more. I’d say your trig is fine; your units awareness could use a touch up though 😉 Or are you talking about the extra distance for a great circle between NYC & LA per **Xema**? ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [December 16, 2011, 2:21pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/17 "2011-12-16T14:21:27Z")
> [@LSLGuy](#): > > I’d say your trig is fine; your units awareness could use a touch up though 😉 More like my reading comprehension. ::tail between legs:: ---
**Author:** ![Brown\_Eyed\_Girl](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brown_eyed_girl/32/3574_2.png) [@Brown\_Eyed\_Girl](https://boards.straightdope.com/u/Brown_Eyed_Girl)\ **Post date:** [December 16, 2011, 2:38pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/18 "2011-12-16T14:38:51Z")
> [@Chessic\_Sense](#): > > That extra three seconds is 264ft, or 88 yards, at 60 mph. What’s that tell us? That slowing to a stop at point B is going to add more time to the total travel time. Assuming, that is, you aren’t blowing through point B at 60 mph like you’re in a drag race. ---
**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\ **Post date:** [December 16, 2011, 2:45pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/19 "2011-12-16T14:45:39Z")
> [@Brown\_Eyed\_Girl](#): > > That slowing to a stop at point B is going to add more time to the total travel time. Assuming, that is, you aren’t blowing through point B at 60 mph like you’re in a drag race. Who said anything about point B being a destination? Unless told otherwise, I’d presume the driver was continuing on to points C, D, and E without stopping. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [December 16, 2011, 2:59pm UTC](https://boards.straightdope.com/t/driving-time-puzzle/606403/20 "2011-12-16T14:59:24Z")
How about the time it takes to get up to 60mph starting from a standstill at point A? You can’t start at point A and instantaneously be going 60mph. [Next page](https://boards.straightdope.com/t/driving-time-puzzle/606403.md?page=2)