North of the M25, the road is a near motorway standard "A" road with all junctions grade-separated via underpasses or flyovers, but curves and gradients a little steeper. There are no hard shoulders but frequent lay-bys. It climbs through the Chiltern Hills then descends into the valley of the River Bulbourne crossing water meadows just outside Hemel Hempstead at Boxmoor. There are grade-separated junctions with the A414, A4251 and A416. The route returns to open country north of here, passing west of Berkhamsted. It passes the National Film Archive. Before Tring, near Wigginton, it crosses the Icknield Way Path and Chiltern Way. An arched footbridge spans the road just near the summit before it passes just east of Tring (for the Ridgeway footpath) and descends the Chiltern scarp into the Vale of Aylesbury.