How exactly is a "measured mile" measured?

[fjlee]

At Bonneville and other LSR sites,  I often see the term "measured mile".

Exactly how is this mile measured?  What is the accepted degree of accuracy that
must be achieved?

Could the same measuring regimen be used to measure and set-up a  "measured 10 mile"....?

Thanks folks.......

FjLee       Denver CO

[John Burk]

Since the 1980s, electronic distance measurement (EDM) devices have allowed surveyors to measure distances more accurately and more efficiently than they can with tapes. To measure the horizontal distance between two points, one surveyor uses an EDM instrument to shoot an energy wave toward a reflector held by the second surveyor. The EDM records the elapsed time between the wave's emission and its return from the reflector. It then calculates distance as a function of the elapsed time. Typical short-range EDMs can be used to measure distances as great as 5 kilometers at accuracies up to one part in 20,000, twice as accurate as taping.

[Stainless1]

They can also measure with GPS. Don't know how they do it at Bonneville or any of the mile and mile n a half tracks.  Watched them survey the neighbors place, the guy said he was accurate to about .100 inch to 3mm...  I didn't do the math for speeds, but that sounds pretty close... especially if you are placing a rod that is about an inch.

[nrhs sales]

are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?

[fjlee]

are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?

"Thank you" for the responses.

I'm asking how the actual distance for the "measured mile"  is determined.

I'm also curious as to how a longer distance would be measured with precision.  Say  10 or 20 miles.

FjLee             Denver CO

[bbarn]

are you asking how they measure the actual distance for the mile or how they measure how fast a vehicle goes thru said mile?

"Thank you" for the responses.

I'm asking how the actual distance for the "measured mile"  is determined.

I'm also curious as to how a longer distance would be measured with precision.  Say  10 or 20 miles.

FjLee             Denver CO

Assumptions: You are talking in a straight line. Line of sight is unobstructed.

GPS measurement would be easiest because you would not need line of sight and could still measure the distance. This would also include elevation changes.

You could use the method above with EDM. While limited to shorter distances than you are talking, you could measure and move the equipment for the next leg. Four or five hops would get you where you need to be.

How accurate do you need to be? You could use a tape measure or a wheel measuring device provided the terrain would support the accuracy you needed. I've laid out a five mile course with an odometer on a car and handheld GPS for bicycling as backup. I don't know that the SCTA or FIA would call that qualified to be record worthy but I can tell you a VASCAR device from a cop car would read the speed to within a mile an hour or two.

What are your goals? what are you trying to accomplish? With a little more context I am sure we can get you what you need or point you in the right direction.

You

[fjlee]

>>>>Assumptions: You are talking in a straight line. Line of sight is unobstructed.

Line of sight=yes, at least for 1 mile.
Line of sight is unobstructed=not necessarily, in the case of  the longer distances.

Let's also assume as measured on B. Salt Flats for an LSR event.

>>>>What are your goals? what are you trying to accomplish?

My goals???   I guess my goal, at least for this posting, is to find out how various distances are measured
and marked, out on the salt, prior to an LSR event.  Especially the distance that'll ultimately be used to calculate
an average speed.

The AMA, FIM, etc.......what level of accuracy do they spell out? 
Is it spelled out in feet and inches.....or is it as a percentage of something?

I find it an interesting mental exercise to realize for instance, that the timers start at POINT A, and timers stop
at POINT B.  A to B is laid out so that it is a straight line 1 mile in length 'tween A and B.  But no
vehicle ever made will travel that AB line in a perfectly straight line.  There hasta be a certain degree of "meander"
to the actual vehicle path.  So the vehicle actually travels more than 1 mile during a timed run.

I'm thinking that the calculations assume it's exactly 1 mile tween A and B.

I think that the measurement of  "time", on the salt, is more accurate than the measurement of "distance".

But that doesn't detract from my enjoyment of any LSR event I've ever watched.

Thanks, folks.......

FjLee          Denver  CO

[Glen]

SCTA=BNI Hires a certified Engineering company from Salt Lake city to survey and mark the courses at Bonneville. Each mile is marked and a survey tag is placed in the salt as well as a red paint strip and a stake.The long course is marked in this order 1 mile, 2 mile 2-1/4 mile 3 mile 4 mile, 5 mile and a 132 trap at end of the 5 mile. This is done on all courses. The 3 mile short courses are only timed to the 3rd mile. There are mile marker flags to the 8 mile for the driver/rider know their position for shut down. If there is a Kilo used for a  international event FIA / FIM it is marked in the center of the mile timing trap in the middle of the course depending how long the over all length of that course is.

[Seldom Seen Slim]

FJ, you're right about the fact that it's danged near impossible for any of us to ride/drive perfectly straight over the mile(s).  The distance is measured between the timing points -- lights, flags, smoke cans, or whatever.  And the vehicle's operator does his best to go straight -- but the wind, the course conditions, the vehicle's handling - and all sorts of other things - help make the traveled distance be a tad (or a bunch) more than a mile.  YMMV -- so to speak.

[Elmo Rodge]

Ok. Do they put 21,120 1-2-3 blocks end to end or do they use a tape measure or do they measure it optically or sonically or GPSally? I'm sorry. I'm having a bit of trouble  seeing the answer to the original question.  Wayno

[Speed Limit 1000]

 Wayno, Maybe a Colorado smoke induced question

[fjlee]

Ok. Do they put 21,120 1-2-3 blocks end to end or do they use a tape measure or do they measure it optically or sonically or GPSally? I'm sorry. I'm having a bit of trouble  seeing the answer to the original question.  Wayno

Dang, Elmo............I like it!!  I had originally thought that for super precision, maybe they used a whole bunch of Jo blocks, wrung together!!

FjLee     Denver CO

[Elmo Rodge]

Wow. The cumulative error would be significantly greater with Jo blocks. 1-2-3 blocks would be bad enough. I bet they have a designated 5,282 foot string and they burn a foot on each end.  Wayno

[Jack Gifford]

I would be interested to know, historically, the measurement schemes used. For instance, in 1914 (I think?) how the distance was measured for the inaugural FIM landspeed record.

[jacksoni]

FJ, you're right about the fact that it's danged near impossible for any of us to ride/drive perfectly straight over the mile(s).  The distance is measured between the timing points -- lights, flags, smoke cans, or whatever.  And the vehicle's operator does his best to go straight -- but the wind, the course conditions, the vehicle's handling - and all sorts of other things - help make the traveled distance be a tad (or a bunch) more than a mile.  YMMV -- so to speak.

If you do the math, is not a lot different( is a "tad"). For instance say the track is 100ft wide and 1 mile long and you start at one edge of the track and end on the other side at the finish line ( and I think generally we do not wander that much) you travel 0.9468feet farther.