Why are physical checks needed?
ISTM that if you used all relevant and already available data (power, height and aerial type of all the towers, topography, population density, cell capacity etc.), a computer algorithm could predict both coverage and average data speeds fairly readily. The physical test described would be far less accurate for any number of reasons - radio shadow areas caused by the car & equipment itself, temporary data congestion causing falsely low rates at the time of the test, belated cell handovers causing the download test to be done on a weak signal when a stronger signal from another cell tower exists. Etc. etc.