I suppose you are on the NA server (http://www.waze.com/dashboard), right? I believe that if you set the “Select Country” on the http://www.waze.com page to USA or Canada, the Dashboard table might switch between imperial and metric values?
No wonder, it’s not your fault, but Waze’s - this menu have to be placed in the Dashboard’s ‘Personal Details’ section, just under the ‘City’ field. Not on some unrelated (main) page.
The setting isn’t on your account, it’s in the browser cookies. So if you use Firefix, IE and Chrome, it has to be set in each of those. Then when you switch to your laptope, you have to set it there too. Same with all 7 of the work computers you use, etc…it can be a pain.
But once it’s set, it should stay set as long as you don’t purge your cookies (sounds like some kind of euphemism for vomiting).
I have to reset it ~daily on FF at home and IE at work and I do not purge cookies at all. It is the only site that does not seem to keep user settings like this. I have no issues with other sites that use cookie based settings.