ddhr.org - Speeding to save time

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Speeding to save time (10)

Jan 22, 2009

I'd like to make the case that speeding, while illegal and dangerous, is incredibly beneficial when done over long distances, assuming one values time, and that conversely, when done over short distances, is relatively useless.

Let's say the distance between my house and my job is 10 miles. And let's say the speed limit is 40 mph. If I drive the speed limit the whole time, my commute will take

(10 miles) x (1 hour/40 miles) x (60 minutes/1 hour) = 15 minutes

Let's say I go 10 over the speed limit, i.e. 50 instead of 40. That means it'll take 12 minutes to get to work. That 25% increase in speed equates to a 20% decrease in time. Not bad, but we're talking pennies here. Three minutes? The $120 speeding ticket doesn't even come close to making it worth it. That's $40 per minute!

But what if, instead of 10 miles, I was driving 100 miles. And again, let's say the speed limit is 40 but I go 50. What would've taken me 150 minutes (2.5 hours) now only takes me 120 minutes (2 hours). It's still a 25% increase in speed and a 20% decrease in time, but suddenly the time is starting to add up. Thirty minutes? I can do a lot with an extra 30 minutes.

Now let's say instead of 10 or 100 miles, I'm driving to Orlando, FL, which is about 1000 miles away. Beep boop beep, multiply by ten and suddenly I've shaved 5 hours off a 25 hour trip (obviously the speed limits are higher, but still).

What we have here is a basic lesson in percentages, specifically the idea that a percentage of a larger number is greater than the same percentage of a smaller number. It's simple, but it says a lot. It says that speeding over short distances is hardly worth the time savings or the potential monetary penalty. But it also says that by speeding over long distances, you can save huge chunks of time, and that regardless of whether you place a higher value on time or money, that $120 speeding ticket could actually be worth 5 extra hours, which is only $24 per hour. You can't argue with math. #travel

Comments

#1	Buzzkill	Jan 22, 2009
	But Dave, speeding is against the law. Shouldn't we abide by the authorities? And besides, look at all the stress it will cause the driver when he sees "smokey" waiting in the median for him to go zipping by. The heart leaping into the throat followed by the palpitations, shallow breathing and sweaty palms as he pulls out behind him and casually gets closer and closer to the speeder. Meanwhile, the speeder is saying to himself, "Oh please no....please...please..no!" It's almost nightmarish! Or so I'm told. :-)

#2	Dave	Jan 22, 2009
	The math has spoken.

#3	Steve	Jan 23, 2009
	oh but wait.. longer.travel time increases the risk of getting a ticket. and even a second ticket.

#4	Rus	Jan 23, 2009
	Dave...I think you need to heed Steve's thoughts and go back to your math. I suggest a .10 probability of a ticket and you should probably include not only the cost of each ticket but also the increase in insurance costs. :-)

#5	Rus	Jan 23, 2009
	(over, say, 10 hours of driving)

#6	Rich	Jan 29, 2009
	See, I've always considered speeding to be more of a safety thing than a time saver. Don't get me wrong, I like the saved time aspect as well. But I stipulate that speeding within certain parameters is actually safer than doing the speed limit or even a little under. Yes, I'm saying that I think speeding can be safer. Here's the logic: First, the limiting factors: weather conditions - if it's dark or slippery speeding is just unsafe. I won't waste everyone's time by explaining why (read as, I originally did, and it doubled the length of this post.) In good weather, with an unobstructed view, in full daylight, I still think there is a safe upper limit, which depends on a number of things - primarily the number and position of surrounding cars. Your own car's capabilities enter into it all last, as far as I'm concerned, since most cars on the road today have pretty similar capabilities. Barring the above, why do I make the seemingly preposterous claim that speeding is safer? Collision cross section and mean free path. (cue the stat-mech lecture) If you consider a tube with a rarefied gas flowing through it, and you pay attention to a specific molecule of that gas, the likelihood of that molecule colliding with another is directly proportional to the amount of time those two particles are near each other. This is their collision cross section. Similarly, the more rarefied that gas is, the greater the distance between any two particles, and thus the fewer collisions that will occur - mean free path. So, the goal, when attempting to drive safely is to minimize the collision cross section with other vehicles, while maximizing the mean free path. The limitations stated earlier place an upper bound on speed, but this is happily well above the speed limit in most places. By driving faster than the group velocity of those cars near you, you reduce your collision cross section with them. Couple this with the fact that people are not as smart as gas particles (I drive in Jersey, you won't be able to convince me otherwise), and tend to do things with their cars that defy comprehension, and you will see why I want to spend as little time near them as possible. Similarly, if you can find that promised land between clusters of cars (which form because people do the opposite of what is safe, and pace each other, forming herds), you can maximize mean free path just by pacing yourself into that gap. It's pretty much nonexistent at rush hour, but if you can find one, it also has the bonus of saving a little gas by reducing braking. I've heard the argument that this is not actually safer because 1. the higher speed reduces reaction time, and 2. the increased momentum will cause greater injury in the event of a collision. 1. is partially true. If you go blasting by someone 40mph faster then them, you don't have enough time to try to avoid any boneheaded thing they may do in the moment that you are next to them. This is why those teenagers in their mostly plastic cars doing over 100mph do not fit into my notion of "Safety Through Speeding." There's no time to get out of their way, and they have no time to react to changing conditions - but I digress. 2. I think, is irrelevant. Are you any less dead from a crash at 65mph than from one at 80mph? I'm curious - do I sound nuts or do I have any converts to "Driving Defensively by Going Real Fast"?

#7	Dave	Jan 30, 2009
	Rich, thanks for being briefer than you could've been. This was similar to one of your comments from over three years ago. Wow that's a long time ago. Congratulations on being consistent. And yes, I agree. Minimizing the chances of interaction with other cars will likely make driving safer, since most motor vehicle accidents occur when two or more vehicles "interact". But whether or not you need to speed in order to do this depends on the road and the time of day. There are certain stretches of the GS Parkway where if you're not going 75 or greater, you're putting yourself in serious danger. And I also agree with your last point: You generally don't need to worry about injuries when you're traveling above, say, 50 mph because you'll be dead no matter what.

#8	Rich	Feb 2, 2009
	I'd totally forgotten that I made that comment. I guess it proves that I could have been even briefer, (more brief?) since I was then. Oh well, it felt good to get it all out.

#9	Rich	Jul 13, 2009
	Looking at only the money aspect of this, there's a nice writeup on thesimpledollar here: http://www.thesimpledollar.com/2009/07/12/how-much-is-your-time-worth-thoughts-on-speeding/ His conclusion is that it's rather more expensive than what you came up with. The analysis is pretty interesting - you may want to give it a look.

#10	Dave	Jul 15, 2009
	Interesting article. I had a hard time getting past the author's use of fractional percentages, but once I swallowed my geekery, he actually had some good points. Gas mileage is something I completely neglected.