November 21, 2010

POSSIBLY IRRITATING ESSAYS: Hurried People and the Half-Time Sprint

Every morning on the way to work, driving at or near the posted speed limit, I am passed by cars sprinting five to ten miles per hour faster than I am. Sometimes these people weave in and out of traffic. Sometimes they lay on the horn at me, as if I am the sole cause of their need to hurry.

Putting aside my own level of irritating and conveniently overlooking the fact that some people drive the speed limit just to bug other drivers, I find myself wondering if going five or ten miles per hour over the speed limit really makes a difference. On the other hand, is going those few miles an hour like a sorcerer’s stone going to work a wizardly miracle of arriving on time to work despite leaving my house late?

To find out if wizardry is possible in this case, I turn to the science of physics. The following simple algebraic equation is something every ninth grader who comes through my science class will learn first semester: the speed of a [car] is equal to the distance [the car travels] divided by the time [it takes to reach your destination]. More simply; s=d/t.

But that’s not relevant here. We want to find out if TIME will get less if my speed is faster. Simple. We rearrange the equation getting [the] time [it takes to get somewhere] is equal to [the] distance [you go] divided by [the] speed [you go]. Again, more simply: t=d/s.

To get the results, we simply plug numbers in. We need to establish something here though. I need to know how fast I drive to work. There are nine stoplights and stop signs on my way to the school I teach at; the speed limit also varies over that distance (which remains a constant eight miles.) So I FIRST need to calculate my average speed. To do that, I’ll also tell you that on a usual morning, it take me twenty minutes to get to work. To do this right, I have to say that twenty minutes is 1/3 of an hour. In decimal, that’s .33 of a hour. So, to math:

s= d/t = 8 miles / .33 hours = 25 miles in an hour (or 25 mph). So my AVERAGE speed, stoplights and different speed limits and all is 25 mph. Now we can get down to business!

Let’s say I bump up my speed 5 mph to an average of 30 mph (which means ROUGHLY that in the SPEED LIMIT 30 zone I drive 35 and SPEED LIMIT 35 zone, I drive 40. HOW MUCH TIME WILL I SAVE?

t = d/s = 8 miles / 30 mph = .27 (remember, that’s .27 of an hour, so I have to times it by 60 minutes: .27 x 60 = 16.2 minutes. Speeding 5 mph faster, I magically save 3.8 minutes! WHEW! What a shave! Hmmm…not what I was hoping for.

All right! How about I get serious here? TEN mph faster! Move my average speed up to 40 (consistently 15 mph over the posted speed limit.)

S=d/t=8 mi/ 40 mph = .2 x 60 = 12 minutes! There we go! I’ve saved EIGHT ENTIRE MINUTES OF MY TIME! (Of course, at those speeds, I’m likely to come to the attention of law enforcement authorities eventually and the ticket for speeding might negate some of the financial gain I receive by being to work consistently on time even though I leave late…)


How about greater distances? I used to go to college in Moorhead, MN. From Minneapolis to Moorhead is 233 miles. Driving the speed limit (which AVERAGES 65 mph including potty breaks, slow downs and yelling at the kids in the back seat…) s=d/t=233/65= 3.58 hours. Speed up to 80: s=d/t=233/80= 2.9 hours for a savings of 42 minutes. Of course, 80 mph is my AVERAGE speed. The “sometimes slow” translates out as potty breaks, so my typical highway full speed travel is roughly 90 mph. Which once again can translate into close encounters of the law enforcement type…)

How about REALLY long trips? I must save time there! NYC to LA: 2784 miles. s=d/t=2784 miles/70 mph = 40 hours.

Speed it up to 80 mph: s=d/t=2784/80 = 34.8 hours. I save 5.2 hours. Hmmm…OK, but not really impressive.

Let’s REALLY speed it up to an average speed of 100 mph: s=d/t=2784/100 = (obviously) 27.84 hours. Savings: 12 hours. Half a day. Maybe worth it, but I can’t imagine my Toyota Sienna van maintaining a steady speed of 100 mph. Plus traveling consistently at that speed seems likely to evoke a SMOKEY AND THE BANDIT effect as I pass like a flash from county to county and state to state.

So the only wizardy that happens here is in my mind: I’ve convinced myself that driving a couple miles an hour faster will MAGICALLY and dramatically change the time it takes to get somewhere. I will SWEAR EMPHATICALLY that the above math can’t possibly be true and that I have had personal experience with the wizardry of driving just a little faster, cutting off just a few people and running just a few red lights and stoplights. I KNOW it makes me get to work on time if I leave late!

My only choices are to continue to test the theory until it fits my perceptions, apply to Hogwarts and put on the choosing cap – or slow down and take it easy.



Paul said...

You could even move this from a psychological discussion, where subjective experience trumps objective reality, to a theological one, where the individual's will attempts to transcend the created order.

Now throw special relativity into the mix and see what happens. If you could drive to school at 0.8c . . .

slxpluvs said...

The traffic light system is set up so that cars travel in "waves." Each wave of traffic is timed so that it can go through as many lights as possible before stopping, or so that the traffic is limited at certain places.

Thus, the goal of speeding is NOT to increase your overall velocity, but to get ahead to the next wave of cars. If I go 3 times faster than you only to be stuck at the same light, my speed doesn't much matter!

The problem, as you began to identify, is that to skip two or more waves requires navigating through each wave. It is only possible to skip to the next wave if you are in the front of the current wave. Getting to the front of the wave may require weaving, rapid acceleration, and dangerous driving. Thus, speeding with the intent to get to your destination faster is unsafe for the driver and those around the driver.

The OTHER reason to speed is that it gives a person more control of the road and is safer when used correctly. A great example of this is motorcycling. If traffic is going 60 and yer going 55 on a motorcycle, then you don't know what you have to deal with next. 8 square inches of mirrors doesn't tell you nearly enough information. People can merge into you or worse.

A motorcycle that is going 65 when traffic is going 60 has the opposite effect. All of the traffic they need to worry about is in front of them, not behind them. They don't have to worry as much about people merging into them because they approach the people merging, not the other way around.

This effect is multiplied as the speed differential increases. At some point, it is as if they are driving around relatively stationary objects. Although there is a higher RISK (accidents at high speeds are bloodier), it puts less risk out of the control of the individual (if they crash or not is their fault).

There are other reasons to drive this way. Usually smaller vehicles are advantaged to drive in these aggressive ways. Although it may also get one to the destination quicker, it is preferred for safety reasons.

In fact, I remember there having been some studies done and most speeding doesn't get people to their destinations any faster because of the effects of "waves" of traffic. A 20% increase of "personal speed limit" results in less than 5% decrease in trip time - the rest of that is WAY more than time dilation. Gosh, I wish I could find a study I could cite for you ........