

Ed Davis drove all day through Qasvin and into the night
 until he reached the Abas-Abas village. If we assume that Ed started at around 8AM-10AM and
 drove until about 8PM-9PM after the sun
 went down in late July, "We arrived at Abas-Abas' village after
 dark" as Ed said, that is around
 10-13 hours of driving. Also, Bob Cornuke stated that Ed drove at least 8-12
 hours the first day before
 arriving at Abas-Abas' village. 
The son of Abas-Abas drove Ed in a British lorry
 starting at around 10PM-Midnight until 6AM-9AM in the morning, "through the night into the
 morning sometime," which is around 6-11 hours of driving. 
The total time in driving was around 16-24 hours. The
 entire distance on the existing 1943 roads from Hamadan through Qazvin to Mount Ararat is 838
 kilometers or 520 miles. 
At an
 average of 40 miles per hour (mph), it would take about 13 hours to cover the
 520 miles. 
At an average of
 30 miles per hour (mph), it would take about 17.3 hours to cover the 520
 miles. 
Even
 at an average of 25 miles per hour (mph), it would only take about 20.8 hours
 to cover the 520 miles,
 which fits comfortably near the middle of the estimated 16-24 hours of total
 driving time. 
If one assumes the longest possible driving time being 24 hours, then the
 Army truck and the British
 lorry would only need to average 21.67 miles per hour over the distance.