Alex
Actually, the A28 is complete from Alencon to Le Mans, joining up with the A11 north of Le Mans, and is a far better road than the N138 (too much heavy traffic and too few dual-carriageways).
Because we stay in a Gite in a small town south of the track, then we carry on the A11 towards Angers. I know the A28 may not be ideal porker territory, but then neither is the N138, sepecially if it rains; I have pulled out from behind a lorry, to be met with a wall of spray, and zero visibility, and this on a one lane each way road.