All routes will be designated with a three-digit number which will provide an indication of the level of service
100’s routes act as the core routes – they will provide service Monday through Saturday throughout the day and into the evening. These routes will also operate on Sunday;
200’s routes provide service along key urban corridors Monday through Saturday during day hours;
300’s routes provide service on the more suburban corridors in the region and operate Monday through Friday during day hours;
400’s routes continue to act as special routes to provide added capacity to meet demand from Allentown School District students;
500’s routes are LANta Flex routes – new flexible, reservation based feeder services designed for more suburban areas; and
600’s routes are circulator and crosstown routes designed to address specific markets.
So the whole numbering system is about service quantity. Clearly, too, the higher numbers mean "don't less this distract you from the more versatile lower-numbered routes," which is exactly the principle of good frequency branding or a good network map such as Portland's (which distinguishes four tiers: light rail, frequent bus, infrequent bus, and peak-only).
Obviously, most agencies would resist the Allentown-style numbering because it means that if you change a service level you need to renumber the route. But if followed through, it would be a step toward branding a core network (presumably also the most frequent) with route numbers, yet another way for that most versatile network to be most visible to customers.
Personally I wouldn't recommend this if it were exclusively about service duration, as the summary states. I'd do it only if it were also about a frequency distinction, or at least an intended one. But it's interesting that while Frequent Networks are intended to be lasting top priorities of an agency, and usually represent permanent strong markets, no agency (in either North America or Australasia) has "locked in" the commitment to a Frequent Network by numbering the frequent lines differently.