they're observing peak time traffic patterns
If you want to know whats causing a road to be busy during peak time traffic, no point asking people who drive on the road at midday where they are going
They did quite a few of these in leeds recently, prior to the openning of the east leeds link road. It links Junction 44 of the M1/A1 Link with leeds city centre. Previously everybody going into leeds from the A1/M1 link had to come off at junction 43 and come in via a dual carriageway, that then merged into 1 lane, that then merged with the a46, the road carrying all the peak time traffic from wakefield into leeds. Funnelling all traffic from wakefield into leeds, and from the M1A1 into leeds, into a single lane meant rush hour traffic was a standstill.
So to find out if this link road would benefit people, they pulled people over during rush hour and asked them where they travel from, and where they travel to. And worked out that most of the traffic could be re-routed through the new leeds link road.
The standard on Censuses is from the 80's so the advice of traffic flows is a bit out. It's in the process of being rewritten.
It openned about a month ago, and my journey into work has halfed now.
Guessing they must be considering building a bypass or new road near you then ?