I have a question on a subject that I haven't been able to figure out on my own.

I haven't been on this forum in a long time, some of you might recall that I was training for a century last year, the "buff epic" in Colorado. Without a car, my ride flaked the week before the event. I rode 100 miles anyway over 2 days however. I succeeded in my goal. The weather over the last winter was particularly cold and lasted particularly long, and as such it was almost a year without riding (i have a physical issue that procludes me from riding in very cold weather like we were having until june here) So it's been a while since riding, and I have recently moved, and what better way to learn the new town than to ride it?

Now to the specifics of my question. I have been riding over 10 miles for the last 2 weeks each day. The new location is 2500 ft lower in altitude meaning more oxygen, less strain on cardio-vascular systems, making for a much easier ride than I'm used to. 10 miles at 7000 ft is rough if you're out of shape. Not only that but this new town is very flat by comparison to Colorado Springs. With both of those things in mind, I don't know how to increase the difficulty of my 20 mile rides. 10 miles is more than easy, I'm not even really getting a workout at the pace that I had more than a year ago, and I'm still really out of shape. In colorado springs it was very easy to say "I want a good workout today, let's go climb a steep hill" or "I want a long ride, let's go out to limon (with a 120 mile straight stretch with a large shoulder of smooth road to ride)" but here, they don't have 10 miles in a straight line anywhere, so I have to ride through town, meaning lights, stops, construction, and without the hills, I don't have anything to climb. The mountains are a 3 hour drive and I have school and a full time job.


TL;DR: How can I get a good workout with these factors? I keep the pace up hard on the 10 miles, I use a higher gear, and I'm consciously pushing myself, but at the end of the ride, I feel like I could go for another 20 and not be fatigued (I just don't have that kind of time now with my current schedule). What can I do to create a challenge with all these road lights, and less than attentive drivers, on flat terrain?

sorry for the long winded nature of the post, but I felt the contrast was necessary to convey my frustration.