When I opened your “beam.png” in Photoshop the actual lights were opaque - there was not a graduated fading transparency (just the “non-light” area was transparent). The attached file is a quickie demo: the beams fade to transparent, but they are not brighter where they overlap.
RoadBeam-trans.hype.zip (44.1 KB)
In Photoshop: Try “File menu > Export > Export As…” where You can explicitly set the PNG file to have transparency (upper right corner with PNG selected as export format).
Also, make sure You do not have the “Automatically optimize when exporting” box checked for this file (“Resources” panel at bottom); otherwise Hype might turn it into a JPEG on export and the transparency will be lost.