There will be four ventilation shafts and one intervention shaft in the tunnel across the Chilterns. These would also be used for emergency access during operation. All the ventilation shafts use the same diaphragm wall construction method. The first of these is in Chesham Lane, Chalfont St Peter. The construction compound will be in place for seven years. Shaft depth is 63 metres. Tunnel boring machines reached here in March 2022. The access route to the compound is via a newly constructed temporary haul road directly to the A413 then to the A40 and the M40. All HGVs will turn left when leaving the haul road. The junction is controlled by temporary traffic lights.

PRoW (Public Right of Way) CSP 10 will be diverted east around the construction compound before joining the existing footpath CSP 9 south of The Brow for the duration of construction and then reinstated along its original alignment.