Hello footprints,
I hope it's not too late to help you with this. I found out about your problem only now, via Google Search. Did you try contacting me for support through the
Contact Form? Because I didn't receive an e-mail from you about this, so naturally I'm curious if there is something broken.
About your problem... it seems there's a small detail missing from Bert's Walkthrough.
To unlock the bridge, you will have to take the machine plans in the Laboratory (also called "Martylab") AND look at them from your inventory. The plans are in the basket under the table. Take them and look at them from within your inventory. After you looked at them your Mission should change to something like "Confront Professor Marty on the Bridge". After that you should see the Bridge on the Elevator too (it's somewhere on the top left area)
If you haven't unlocked the Laboratory yet, please do so. Bert's Walkthrough explains how.
Let me know if you have any other problems, I'd be happy to help.
Thanks for your support
Rainer (Ray) from Spreadcamp