I corrected also some bridges lengths to avoid glitches.
Beautiful. No longer will towns build ugly too-short or too-long Tied Arch bridges
I'd prefer keeping them to length 5 (+2 heads) exactly, but length 3 or 4 looks good enough too.
Bug report! Tubular silicon bridges are coming available in 2020 along with the tubular steel. According to your readme the silicon bridge should not be available until 2040. Otherwise, fantastic!
Edit: Also, several bridges don't seem to have a maximum length set. I should only be able to build a steel tubular bridge longer than 32, but I still get options for silicon tubular, concrete viaduct, modern suspension, steel cantilever, and steel suspension. In fact I can go as long as I want with all of these, including the steel tubular which should be maxed at 64...