Why did the geese cross the road?

There are lots of lakes and ponds in Reston and we have got used to seeing Canada Geese paddling in roadside puddles and grazing on grass verges .  

This evening, however, as we slowed down approaching a red light on a dual carriageway between the airport toll road and Reston town centre (above, but taken from the other direction) we saw a tiny convoy ahead - a family of five - fairly oblivious of the traffic bearing down on them.

They had crossed one half of the road when we saw them and luckily set off across the second half before the traffic had started moving when the lights changed ..