Last Friday I handed each of my patrols 50 cable ties and a drawing of a trestle(PDF), and told them to get ready for a chariot race. I have heard stories about Scouts in Europe using the heavy duty 'hand-cuff' cable ties for pioneering, and I was curious to see how the small ones would hold up. After a couple of minutes figuring out how to tie lashings with them, the trestles were built fairly quickly and the patrols were ready for a race around the hall, carrying a patrol member on the trestle. The photo at left is a trestle AFTER the race, so the cable ties seem fairly sturdy.
Here are details of 4 different lashings (clockwise from top left) - a diagonal-style lashing (not recommended for reasons explained below), a diagonal-style lashing with frapping, a square lashing with frapping and finally, what I like to think of as a 'Be Prepared' lashing rather than a 'Scout is thrifty' lashing. You will probably need to join a couple of cable ties together to make a chain long enough to tie a lashing around the poles. Use thin poles if you can- bamboo, thatching laths, scout staves or scantlings.
One word of warning: if one tie fails, the whole structure can fail very quickly. At the end of our race we noticed one patrol was missing, they eventually arrived with their trestle looking like this. For the record, they were using un-frapped diagonal lashings. The other 4 patrols completed the course safely. For a first time experiment, 80% is not a bad success rate.
If you're thinking of giving this a try, Wikipedia says that the black ties are the best for long-term outdoor use, although I think the coloured ones would be more fun. Once you've tried it or if you've done some cable tie pioneering already, let me know how it works out. (I'm also curious about how the wrap-around velcro ties will work but I don't really have the budget for 50 of them to test this idea)