The River Misbourne diverted via culverts under the M25
The Chalfont Viaduct is built of blue and black engineering brick with additional decorative brickwork. The bridge is approximately 12.5 metres (41 ft) high, although it varies in height due to changing ground level, and it has five semi-elliptical arches, each 15.5 metres (51 ft) wide. It was constructed between 1902 and 1906 by the Great Western Railway (GWR) to carry trains on the Great Western and Great Central Joint Railway between London and High Wycombe across the River Misbourne. It was designed by James Charles Inglis, chief civil engineer of the GWR, and assistant engineer Robert Cherry Sikes.
In the mid-1980s the construction of the M25 motorway required the Misbourne to be diverted via underground concrete culverts. The route of the motorway was aligned to pass through the arches of the Chalfont Viaduct, leaving the viaduct largely unaltered apart from the raised ground level and the addition of concrete supports and crash barriers. The viaduct is the only brick-built bridge on this section of the M25.