200 runners, 32 miles, 1 big communications challenge

This article is expected to be published in a slightly amended form in the magazine distributed to those who register to participate in the Dartmoor Discovery Ultra-Marathon in 2012. I thought I'd put it up here too for anyone else who is interested.

The Dartmoor Discovery Ultra-Marathon is a gruelling challenge for all of the runners who take part: the 200 runners have to run 32 miles up and down hills on Dartmoor, with the course fluctuating between 415m and 60m ASL.

In many ways it is as much a challenge for the Dartmoor Radio Club, who ensure that runners complete the race safely, arrange minibus collection for drop-outs and coordinate the St. John's Ambulance where necessary. The group's role also extends to passing the numbers of each runner to the race commentator just before they arrive at the finish.

The poor mobile telephone coverage over much of Dartmoor means that a dedicated communications network for the race is indispensible, but setting up such a network is made particularly challenging by the terrain: about one-third of the course (principally the section between Ashburton and Widecombe) is not within direct radio coverage of the start/finish in Princetown.

Over several years assisting in the race, the volunteers in the club have refined a plan for overcoming these difficulties:

One club member travels in a car in front of the runners, and other in a sweep car. These vehicles are in communication with a site at Buckland Beacon, to the east of the course, which has better coverage of the course than can be achieved from Princetown. The person at Buckland Beacon is able to relay messages from the cars to Princetown.
At various points around the course (all of which are known to be within range of Princetown), other club members report the runner numbers of each participant as they pass the checkpoint.
Another club member is positioned about half a mile before the finish line, so that the numbers of each finisher can be fed to the commentator.
St. John's Ambulance vehicles regularly telephone the Radio Club to report their positions.
In 2011, for the first time, we installed a beacon in one of the minibuses, which reports the GPS location of the minibus back to Princetown automatically every three minutes. This ensured that when runners needed to be collected, we knew where the minibus was. The beacon experiment was successful, and so we plan to install beacons in more vehicles for the 2012 race.

Map showing position of the sweep minibus

A GPS-linked radio beacon in the sweep minibus allows the Communications Centre to ensure drop-outs are collected.

In the Communications Centre, which was located in Princetown Methodist Hall in 2011, all of this information is amalgamated using software written especially for the race by yours truly.

The software performs several tasks:

The locations of each runner are plotted in Google Earth, based on the runner's calculated average speed over the course. The average speed is updated whenever the runner is reported by a checkpoint. (At the start of the race, the average speed for all runners in 2008 is used by default, except for the top and bottom 20 runners in the previous year's results, for whom their average speed last year is used.) The map is redrawn with the latest locations every 3 minutes throughout the race.
If a runner is not reported by the next checkpoint within a certain time of being reported at the previous checkpoint, the software alerts us automatically that a runner might in difficulty.
The software logs which participants have dropped out of the race, and whether they need collection.
Finish-line ETAs are calculated for every runner when they reach each checkpoint. These ETAs are passed to the race organisers to assist in administration. In the last three years, the estimate made 10 miles before the finish line has consistently been within 6 minutes of the winner's actual finish time.

(Because it contains real data from the 2011 race, some data has been redacted from the screenshot showing the missing runners alert above.
The version of the Google Earth map as displayed in the Communications Centre has an Ordinance Survey map overlay, instead of the standard satellite imagery. For copyright reasons, the OS overlay cannot be reproduced here.)