The current, temporary light is at the intersection of Magazine and Memorial Drive. Once the pede bridge is completed, the temporary light (installed by the DCR contractor) will be removed. Many in the C'port neighborhood like the light better than bridge. The Cambridge City Council put in an order in February 2011 to ask about a permanent light. The city manager's reply was a no can do. (http://www2.cambridgema.gov/cityClerk/cmLetter.cfm?action=search&item_id=20499)
Note this response letter from November of 2011 says the pedestrian bridge will be completed in April.

This appears settled