Measuring for Certification

by Jim Gilmer

(The third in a series of three articles on measuring courses for USATF certification.)


The first two articles in this three-part series on road race course certification dealt with the underlying rationale and fundamental principles of certifying courses. This final article discusses the method and process for conducting a certification measurement of a road course — as well as a calibration course, which is the prerequisite the road course measurement.1 We begin with an overview of the basic method and the equipment needed for calibrating the bicycle and measuring the course itself.

What is the general procedure for certifying a road race course?

The Calibrated Bicycle Method. The only set of procedures for measuring a road course recognized by both USATF and IAAF, the sport’s official sanctioning organizations, is based on the Calibrated Bicycle Method. This method is based on a mechanical digital counter called a Jones Counter2 mounted on the front hub a bicycle. (See Fig. 1.)

Fig. 1 - Jones Counter mounted on a bicycle

A metal tab, called a “tang”, extends from the device’s large gear into the spokes of the front wheel. As the wheel moves the gear rotates a smaller gear that moves the digital counter’s cylinders inside the metal housing. A counter can have either five or six cylinders arrayed in a base-10 numbering system with each cylinder displaying digits or “counts” from 0 to 9. (See Fig. 2.) As the bike rolls forward on the pavement, the number on the counter increases — or decreases if the bike moves backward. Importantly, the change in each count corresponds to a discrete length that the tire has moved across the surface of the road. That discrete length, however, depends on several factors, including: the radius of the wheel; the air pressure in the tire (assuming it’s pneumatic); the load on the tires (weight of the frame plus the rider and any additional weight -- packs, bags, etc; and, finally, change in the pavement temperature over the duration of the measurement.

Fig. 2 - Jones Counter

The Calibration Course. Every certification measurement begins and ends at the “cal course” — with occasionally a visit in-between, especially on courses of greater lengths such as marathons and ultras. A calibration course is defined as the distance between two fixed points on a straight, relatively flat of section road that has been accurately measured with a steel tape, with the measurement corrected for the temperature of the pavement.2 Calibrating the bicycle is performed by riding between the two endpoints and recording the number of counts in the interval. (Alternatively, a calibration course can be measured by a professional surveyor using an electronic distance meter (EDM), but in practice nearly all calibration courses are measured using the temperature-corrected steel tape technique.4 The calibration course itself can be certified if it will be used for more than one course measurement.

USATF and IAAF regulations require the calibration course to be at least 300 meters long. Most U.S. cal courses are 1000 ft (304.8 m) in length, although a few have been certified at distances as long as 1 km or ½ mile.5 The endpoints of the course course are usually marked with survey nails driven into the pavement. But for lasting endpoints that won’t get pulled up by a snowplow blade, cal courses can be measured at odd distances between two permanent features of the roadway, such as storm drains, utility covers or pavement seams or joints.

Fig. 2 - Calibration of the bicycle

Fig. 2 illustrates the process of calibrating a bicycle using the Jones Counter.[1] Essentially, the bicycle and measurer become an integrated mobile measuring instrument in the calibration process. And, because the distance between the two endpoints was previously measured independently by steel tape, the the interval of counts between the two points is easily converted into a preferred unit of measurement, whether feet/miles or meters/kilometers.

Pre-calibration: Calculating the Working Constant. The key metric in measuring a road course is the working constant. This number is calculated by averaging the number of counts per ride over the four (4) rides the previously measured calibration course and scaling it up to a standard distance in the selected unit of measurement, such as the number of counts per mile or per kilometer. This is done by multiplying the average by the factor of the cal course length relative to a kilometer or a mile.  For example, the scaling factor for a 300 m cal course in a 1 km working constant is 3.333 1000mcapture.JPG or 5.28 for a 1 mi constant over a 1000 ft cal course5280mcapture.JPG.  Then, to build in a safety margin for the road course measurement, this product is then increased by 1/1000th — known as the the Short Course Prevention Factor or SCPF. 

Fig. 3, below, shows an example of the four calibration rides recorded over a 300 m course.

Fig. 3 Four Pre-measurement Calibration Rides

Using this example, the following formula shows the calculation of a one kilometer working constant with the SCPF:

The working constant can then used to calculate the total counts needed to measure the entire course, in this case, 5 kilometers:

In practice, the numbers to the right of the decimal total would be rounded up to the nearest whole count. Thus 47,085 counts would constitute the number of counts needed to measure of a 5 km course to certification standards based on this calibration. As for the intermediate splits, if kilometers were desired, the four km splits would be 9,416 counts apart, each accounting for one-fifth of the total distance.  If mile splits were desired, the conversion would require multiplying the working constant by a factor of 1.609344 — the number of kilometers in a mile, as shown below:

Again, in practice the mile splits are rounded to 15,155 counts for each of the three mile splits in a 5 km course.

Measuring the Course. Having completed the pre-calibration measurement,  the bicycle is ready to measure the course. A road course can be measured from the Start to the Finish or Finish to Start. It can even be measured in discrete segments that sum to the total length. Irrespective of the approach taken, the fundamental requirements of the measurement are that: 1) the course is measured twice in independent rides7; and, 2) the ridden path of the measurement follow the the shortest possible route that a runner can legally run — the SPR. Let’s examine at these critical standards separately.

1) Independent measurements. The two measurement rides can be completed by the same person or by a team of two (or more) measurers.8 The first measurement, called the “layout ride”, establishes a provisional length of the course based on the working constant established in the pre-measurement calibration. The second measurement, called the “validation ride”, is a check on the reliability of the layout measurement. After completing the rides the two measurements are evaluated. In comparing the distances recorded by each ride, the percent agreement between them, also called the “tolerance”, must be within 0.08% (< 0.0008).

Using the example of a 10K course, if the layout ride produced a measured distance of exactly 10.00 km, the validation measurement must be ±10 m of that distance. Specifically, for the measurement to be considered valid for purposes of certifying the course, the measured distance produced by the validation ride must be more than 9,992 m and less than 10,008 m. The formula for calculating the measurement comparison percent agreement or tolerance statistic is shown below:

Assuming the two measurements are within tolerance, the question becomes which one should be selected as the measured distance to use in certifying the course. Of the three available options — the shorter distance, the longer one, or the average of both — USATF and IAAF procedures require selection of the shorter measurement. The rationale supporting this regulation is that an athlete who follows the shortest possible legal route of the course will have run at least the advertised distance. This reduces the chance that the course will be found short of the distance for which a record is being sought, and increases the likelihood that the course will withstand the scrutiny of post-race verification measurement which the sanctioning body may require before a record performance is recognized.)

An example should help clarify the reasoning behind this. Let’s assume the first measurement of a course to be used in a 10K competition laid out an SPR of 9,999 meters.  The second, or validation, measurement produced a length of 10,005 meters. In this example, adjusting the course by adding 1 meter to the measured route would ensure that the advertised 10 km distance is covered, even if the “actual” length of the course was over 10,000 m. But what if both measurements were long? That is, if both are over 10,000 meters? The same logic still applies. The lesser of the two measured distances would be selected as the measured distance and the subsequent adjustment would shorten the measured route by the amount necessary to  to meet the requirements of the advertised 10K distance.

2) Shortest Possible Route. The ability of the measurer to conduct an accurate SPR measurement depends heavily on the nature of the course. For instance, a course comprising a series of loops with multiple turns is understandably more complex, and thus more difficult to measure, than a partial loop or a straight out-and-back route. Ultimately, course measurement is best learned by doing the thing. Certainly the intended route must be firmly “mapped” in the measurer’s mind. But there’s also the more immediate need to keep track of how many counts until the next split, or turnaround or end of the measurement. And always, always, being aware of traffic. The measurer’s ability to maintain steady-state situational awareness, to minimize distractions and simultaneously carry out multiple tasks that require both mental attention and physical dexterity, all while riding a bicycle against traffic, and getting honked/yelled at for violating the etiquette of the road is a skill honed more through experience than by simply following the procedures manual.

The SPR is central tenet of course certification. Put another way, the SPR is the backbone of recordkeeping for the sport. If not for the SPR requirement, it would be difficult to ascertain if not impossible to ascertain the comparability of courses because there would be no standard against which to evaluate this 5K vs that 5K. The SPR standard may not be perfect but it is the most reliable and common-sense solution to the problem of accurately measuring road courses that can be compared (as compared to performances on the track where the prescribed, symmetric form of the oval is the standard.) Perhaps a day will come when athletes will wear GPS transponders that very accurately measure the distance run between start and finish. But until then, the measured SPR is the best alternative.

Post-calibration: Calculating the Finish Constant — and the Constant of the Day. 

Every certification measurement ends with a return trip to the cal course for the post-measurement calibration — or post-cal, for short — in order to calculate the “finish constant.” This final set of four rides serves as a check on the accuracy of the working constant use in calculating the preliminary measured length of the course. Of the two calibration measures, the one producing the greater value becomes the “constant for the day” for purposes of calculating the final measured length of the course. Why? Because the larger constant would require the bicycle to have travelled farther in covering the desired (advertised) distance, and thus would be less likely to result in a short course if the measurement were repeated in what is known as a “verification” measurement when a performance is “pending” after the record has been applied for.

In general, three situations are capable of resulting in a finish constant value that is larger than the working constant. Of these, the least likely is that the measurer rode the pre-calibration in a sloppy manner, weaving back and forth over the cal course thus producing a measurement that was artificially long, compared to one ridden in a straighter line between the cal course end points.

The two more likely scenarios for producing a finish constant larger than the working constant stem from the fact that  most certification measurements are conducted using a bicycle equipped with pneumatic tires, rather than solid ones. Many, if not most, pre-calibration measurements are completed during the morning hours before the sun has heated the surface of the pavement. Similarly, most post-calibrations are done later in the day on hotter pavement. Physics dictates how pavement temperature and friction affect the expansion and contraction air-inflated tires. As a rule, post-calibrating on a hotter pavement surface requires fewer counts to travel the same distance as compared to the cooler surface of earlier rides.

Occasionally, however, the usual “cooler-earlier-warmer-later” pattern of pavement temperature is reversed. For instance, if a rain shower occurs between the pre- and post-calibrations, the latter can produce the larger constant. Or, for measurements conducted overnight in highly-trafficked urban areas, a bicycle pre-calibrated in the evening before the road surface has cooled but post-calibrated on colder pavement before sunrise is likely to produce a finish constant that will become the constant for the day in determining the final measurement of the course.

In the event that the finish constant is the constant for the day, the measured distance obtained from the two earlier rides of the course must be recalculated. This recalculation will require a return to the course, and adjusting either start or the finish, or relocating a turnaround point, if the course has is one. Usually an adjustment of the course based on the post-calibration is minimal, but does it does entail changes to the physical location of key points on the course as well as the documentation of the affected points prior to mapping the course for certification.

Last but not least, the post-cal requirement serves as a check in determining whether or not an equipment malfunction may have occurred, such as a slow leak from the front tire during the course measurements or as a result of a “slippage” of the Jones counter’s tang between spokes of the bicycle wheel, or other type of counter failure that might not have been noticed during the measurement activity. In this case, the entire measurement must be discarded and repeated after the equipment failure has been corrected.

After making any adjustments to the course required resulting from the post-calibration, it’s time to go recheck all the numbers using a computer. Then, the course map is drawn and all the key points are documented.  Mapping is a topic for a separate discussion in a future article.

[1] This discussion is extracted from a more detailed, step-by-step description that can be found online in the USATF Course Procedures Measurement Manual.

[2] The Jones Counter was invented by Alan and Clain Jones. For an interesting and informative history of the device see History of the Jones Counter by Alan Jones.

[3] The steel tape should be at least 25 m long. (Fiberglass tapes are unacceptable.) The most commonly used tape lengths are 100’ or 30 m. The tape must also be stretched to a tension or force (lbf or pounds of force) recommended for the length and heaviness of the tape. For example, a 100’ standard steel tape should be stretched to 10 lbf as measured by a spring balance or fish scale.

Two measurements of the steel-taped calibration course are made and the average raw length is corrected for temperature, because a steel tape contracts in temperatures less than 68° F (20° C) and expands in temperatures above that.#  The formulas for determining temperature correction factors in celsius and fahrenheit are shown below:

Correction factor (celsius) = ([Temp℃ − 20] × 0.0000116) + 1

Correction factor (fahrenheit) = ([Temp℉ − 68] × 0.00000645) + 1

The temperature-corrected measurement of the calibration course is then obtained by multiplying the correction factor by average raw measurement of the course. To get an idea of what this means practically, if the average raw (laid out) measurement of a calibration course is 1000’ at a temperature of 50°F, an additional 1.4” would have to be added to bring the corrected measurement of the course up to 1000’. A small additional taped distance may be added to bring the course length to a rounded distance, such as 300 m or 1000 ft (304.8 m), the lengths of the most calibration courses.

The calibration course itself can be certified and used in calibrating for the measurement of other road courses, but if not, it is considered a “one-time use” course.  A more detailed discussion calibration courses can be found in the section of the Course Measurement Procedures Manual headed Laying Out a Calibration Course.

[4] For a basic discussion of electronic distance measurement, see What is EDM in survey?

[5] Sixty percent of the 2,853 USATF active certified calibration courses as of this writing are 300 m to 1000’ (304.8 m) in length.

[6] This illustration is from “By the Book”, and article published by the Association of International Marathons and Distance Races. Used by permission.

Jim Gilmer has certified more than 225 courses since he began measuring in 1995. He is the USATF Regional Certifier for New York and an IAAF Grade A Measurer. In 2018, Jim was awarded the USATF/RRTC Ted Corbitt award for his contribution to course measurement and this year was the recipient of the President’s Award by the USATF Adirondack Association

Part 1: Why Certify? What is course certification? Why certify road running courses?  (Link is  )

Part 2: Requirements of Course Certification - understanding of the official USATF regulations governing course certification (Link for this: )


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