Possibly useful data:

Gloucestershire County Council Highways use a figure of 8 car journeys per household per day when calculating road use. They also have figures for the recommended maximum traffic volume for a particular road or class of road. If the construction of a number of new dwellings would cause this number to be exceeded for the road that would serve the dwellings, it may be grounds for complaint.

It is quite likely that Highways does not have up to date traffic survey data for all the the roads in it's area. Contact the Area Traffic Manager to see if information is available. If not, it should be possible to request that a survey be carried out.