Emergency services over here only use the sirens when there's traffic ahead that need to be warned of the fast approaching vehicle. I haven't watched the video but I'm guessing there were no vehicles at the crossroads so they switched them off.

 

Its the same logic I was taught when I was taking driving lessons, if there's nobody around to witness a turn signal (say on a small residential road) then whats the point putting it on?

 

They do the same thing in Aus, I live down the road (like less then 100 meters) from a retirement centre and why an ambulance responsed there they always turn of the siren and the lights, this is when they turn in front of my house 

*Update* - Another video uploaded as of 8/2/2014.

 

This time it's with the Met at night time on a response to an idiot who thought it would be a good idea to intrude on a police station!

Always good fun going on a blue light run, especially with traffic who love to put their foot down and show off!