I know the section of the trail Kieth is talking about, since I use the 520 trail quite often to get from Redmond to Bellevue. (This is a trail which parallels a 6 lane divided, limited access highway, so bikes aren't allowed on the roadway). I understand why the planners built things the way they did (crosswalk, as opposed to tunnel under the street.) The crossing roadway is pretty large at all the intersections of the trail, because it's an entrance/exit to SR-520. 2 lanes each direction, plus a turn lane each way, for a total of 6 lanes. It was an expense decision because tunnels would have been too costly.

I'm not a big fan of the crossings, either. I was nearly clipped by a car at the 51st Ave crossing on Sunday. I was at the intersection with 3 other cyclists, and when the crosswalk light gave us ROW, I started across. A driver exiting the highway (ramp to our left) made a no-stop, no-look, right-on-red and had to swerve to keep from hitting me. Silly of me to assume that seeing her far back down the ramp, and me having the ROW, I could avoid becoming street pizza...

Although the crossings can be kinda sketchy, especially during rush hour when 520 is all bunged up, the 520 Trail is a pretty nice accomodation to have for cyclists who don't want to take the alternate surface streets between Redmond and Bellevue. (It actually goes all the way to the floating bridge, with a bus stop at either end so you can hop the bus across the bridge, which currently bans bicycles.)