Analyzing long-distance travel demand has become increasingly relevant because the share of traffic induced by
journeys related to remote activities which are not part of daily life is growing. In today’s mobile world, such
journeys are responsible for almost 50 percent of all traffic. Traditionally, surveys have been used to gather data
needed to analyze travel demand. Due to the high response burden and memory issues, respondents are known
to underreport their number of long-distance journeys. The question of the actual number of long-distance
journeys therefore remains unanswered without additional data sources. This paper is the first to quantify the
underreporting of long-distance tour frequencies in travel diaries. We took a sample of mobile phone billing data
covering five months and compared the observed long-distance travel with the results of a national travel survey
covering the same period and the same country. The comparison shows that most of the estimates of the number
of missing tours by researchers have thus been too low. Our work suggests that the actual number of longdistance journeys is twice as high as that reported in surveys. Two different causes of underreporting were
identified. Firstly, soft refusers travelled long distances but reported no long-distance tours. Secondly, respondents underestimated their number of long-distance tours. Consequently, there is a need to use alternative
data sources in order to gain better estimates of long-distance travel demand
