The actual distance between the two towns is 50 statute miles. You are correct that it may be more than an hour drive, since there are (and were) a few stop signs and stop lights and some speed limits lower than 55 mph.
Traffic today is indeed much heavier than it was in the 1970's. Back in 1975, a drive on Highway 97 would have been a fairly easy trip.
I don't think, however, that the time of the drive (whether an hour or two hours) between Littlestown and Wheaton would have been critical to an abductor who might have chosen to make that drive. He likely would have taken his time and would have been careful not to attract any attention by speeding or driving recklessly.
In Tracy's case, the more critical time and distance would have been the amount of time that it took to get her from Littlestown to the Maryland state line - which would have been only a few minutes.
I do not know how long she was missing before police were contacted, but it was probably long after her abductor had driven into Maryland with her, and hence out of their jurisdiciton for pursuit.
I don't know if you have ever driven on that route before but it absolutely is well over an hour.
I am not saying it is not connected to the Lyon sisters but for those not familiar with the route between Wheaton and Littlestown it not like you jump on a highway and it's a straight shot. 97 (Georgia Ave) in DC turns into a much more rural area the further north you go.
I just don't want people to have the perception that it is a quick trip or that you'd just end up in Littlestown via Wheaton.