A lot of people, are very surprised when 3D printers are able to span wide gaps without much issue. These guys were able to span about 150mm across a bridge and still get the print to complete. I know in most designs, this isn’t really needed - but it’s worth a look at the pictures at least showing it can be done. 
http://www.3dgeni.us/a-bridge-too-far
Proper tuning is HIGHLY underestimated.
I really need to add a computer controlled fan to my printer… and get bridging properly calibrated…
It’s all about die swell.
So I had to go read-up on die swell and after understanding that, it seems like there’s another whole level of manufacturing knowledge we should have when it comes to tweaking the print process to optimize output.
I’d struggled with bridging in the past and stumbled into just slowing the print down while printing at thicker layer heights.
@Whosa_whatsis do you know if there is a big difference in die swell between PLA and ABS? I’m thinking that if there is, maybe this should be an option in the slicing software. It is noticeably absent in Slic3r and Cura (or I’ve missed them) so perhaps it is a non-issue.
@SirGeekALot Die swell is affected by the formula and temperature (viscosity), extrusion speed, nozzle geometry, etc. I suspect that at specific temperatures for each material, you could get them to exhibit the same die swell from the same extruder, at least for a given extrusion speed.
The trick to getting great bridging is to balance the stretch of the filament, accounting for die swell which causes it to shrink axially as it expands radially, so that the strands stretch tight across the gap but don’t break.