The planned refurbishment of the Darlington Nuclear Generating Station (DNGS) by the Ontario Power Generation (OPG), scheduled to commence in late-2016 and extend until 2026, will result in significant employment growth and increased traffic volumes that cannot be supported by the area's roadway network. In particular, the original Highway 401/Holt Road interchange, located approximately 40 km east of Toronto and serving as the primary access route for employee traffic into and out of the DNGS, was in need of significant upgrade and improvement in advance of commencing the refurbishment. The original interchange provided partial access to the highway only, while an intersection between an adjacent service road and the eastbound off-ramp was considered both unconventional and potentially hazardous to drivers unfamiliar with the unique configuration. Further, the original Holt Road underpass structure precluded the necessary capacity additions required along both the crossing road and Highway 401 through the interchange. Consequently, the Ontario Ministry of Transportation (MTO) hired AECOM to provide Preliminary and Detail Design services for upgrading of the Highway 401/Holt Road interchange to address both the existing concerns and meet the future requirements of the area. The recommended design included provision of roundabouts at both the north and south ramp terminals, and a third successive multi-lane roundabout at a service road directly south of the interchange. The provision of roundabouts at freeway ramp terminals, in place of traffic signals, represents the first time such a design has been used on an MTO facility.
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