The M10 spur was built as a motorway because it inevitably led to the M1, but as non-motorway traffic could now travel between the A414 at Hemel Hempstead and Park Street Roundabout without having to access the M1, the M10 was downgraded to an A road, and designated as part of the A414 to allow for this. The widening or replacement of eleven underbridges on one or both carriageways, and replacing seven overbridges at a cost of £294 million. A variable mandatory speed limit system was installed, making this the first Smart Motorway scheme on the M1.