Accurately measuring trail running courses has historically been a challenging task, particularly on rugged and mountainous terrain. However, the advent of Global Positioning System (GPS) technology has made it easier for runners to obtain precise distances, even on challenging courses. In the Tucson Trail Run Series (TTRS), for example, runners now have the ability to determine exact distances on rocky trails using GPS, effectively using their own running data to measure the course. This is a significant improvement over previous methods, where estimations were made using maps or traditional techniques.
The Tucson Trail Run Series was initiated in the late 1970s by Ken Young. He mapped the original routes based on the Southern Arizona Hiking Club’s maps, which had trails and estimated distances marked in red. Ken used these estimates, along with calculated climbs derived from topographic maps, to establish the trail routes. These measurements were largely traditional, similar to methods employed by the National Forest and National Park trail builders for many years. However, the introduction of handheld GPS units in the 1990s allowed runners to compare their data with existing maps, which in turn provided a reliable way to assess the accuracy of the new technology. Various individuals, such as Wayne Coates and Duane Arter, contributed to the further mapping and development of trail courses using GPS, laying the groundwork for more accurate course measurements.
GPS devices function by triangulating a user’s position in relation to satellites orbiting the Earth. At least four satellite connections are typically required for an accurate reading. Early versions of GPS devices faced difficulties when terrain like trees or cliffs obstructed the signal. However, newer models come equipped with advanced radio circuits that enhance signal reception and accuracy, even in challenging conditions. This improvement has significantly boosted the reliability of GPS technology in measuring trail courses.
Ross Zimmerman, who co-administrates the TTRS, is responsible for creating most of the maps used by participants. Over the past decade, he has worked with several different GPS models, currently favoring the Garmin 60CSx. This model is known for its ability to maintain a strong signal, even under difficult conditions, and it is capable of connecting to numerous satellites simultaneously. This reliable connectivity ensures consistent and accurate measurements, an important feature for trail running, where runners need precise data on distance, elevation, and other metrics.
GPS units can store data in a “track log,” which records the user’s position at specified intervals, allowing for continuous updates on distance, speed, and elevation. For more detailed analysis, GPS data can be transferred to a computer and used with mapping software, such as Delorme, Maptech, or TopoFusion. These software tools enable further refinement and adjustment of the GPS data, making it easier to analyze and correct any potential errors.
Garmin remains a leader in the GPS market, known for producing devices that are user-friendly and accurate. The Garmin 60CSx, while aimed at experienced GPS users, is just one of many options available. Garmin also offers sport-specific devices, such as wrist-worn models for runners (Forerunner series) and cyclists (Edge series). These models provide users with software designed to analyze GPS data in ways tailored to their particular sport, making them a popular choice for athletes seeking to measure their performance.
When preparing for a run or ride, Ross clears the counters and logs on his GPS unit to ensure fresh data. Throughout the activity, the GPS provides real-time updates on distance, speed, and elevation changes. This information is invaluable for runners and cyclists who rely on accurate data to track their progress. In some cases, Ross has compared the GPS data from his runs with his bike computer, particularly during long-distance events like the Death Ride in California, where both devices were used to measure the distance. Such comparisons allow for a deeper understanding of how GPS devices perform over varied terrains and distances.
Although GPS technology has advanced significantly, it is not without its limitations. The accuracy of GPS readings depends largely on the number of satellites the device can connect to, with three satellites providing a basic 2D reading and four offering a more accurate 3D result. Even with the improvements in GPS technology, there are still instances where GPS readings can be skewed, particularly in mountainous areas where terrain changes may confuse the device. This is especially true for switchbacks, where the GPS may struggle to accurately track the user’s position. Ross has found that GPS readings, while generally reliable, may occasionally produce estimates that are slightly off, particularly in elevation tracking. To address this, he uses GPS devices equipped with barometric altimeters, which provide more accurate elevation data.
Following a run or ride, Ross downloads the GPS track log into mapping software, such as Maptech Terrain Navigator or MacGPS Pro. These programs often calculate slightly different, but generally more accurate, trip distances than the GPS unit’s trip meter. By adding up all the track points, the software provides a more precise measurement of the route. This process ensures that the data is as accurate as possible, allowing for a better understanding of the course.
One persistent issue for some users is the loss of signal due to obstacles like trees or canyon walls. While older GPS models were more prone to signal loss in such conditions, newer models have improved significantly. Devices with advanced radio receivers are better equipped to maintain connections with satellites, reducing the likelihood of signal dropouts. However, when signal loss does occur, it is usually temporary, and the device can quickly reconnect when repositioned.
Despite the strides made in GPS technology, it remains imperfect compared to more traditional measurement methods like calibrated bike wheels or steel tape. Until the next generation of GPS satellites and receivers are introduced, some discrepancies will persist, particularly on challenging courses. To mitigate this, a short-course prevention factor could be applied. For example, if the current prevention factor were doubled, it would ensure that race courses measure at least the advertised distance, helping to eliminate uncertainty.
In trail running, the use of GPS technology has become a common topic of discussion. Runners often share their data, comparing distances, elevations, and total climb to create a comprehensive profile of the course. This data helps remove much of the guesswork from trail running, making it easier to determine whether great performances are due to the runner’s abilities or simply a short course. By continuously re-evaluating the course measurements, event organizers can ensure that each race is as fair and accurate as possible.
This article was written by Andy Milroy, Ken Young, and Ross Zimmerman.