Abstract Manager

The Highway 401 Expansion project was a design-build project to widen a 18km long segment of the 401 from the Credit River in Mississauga to Regional Road 25 in Milton. The highway mainline was widened from 3 lanes to 5 lanes or from 3 lanes to 6 lanes in the express/collector sections. The project, with a total budget of $640M, was designed and built under a very aggressive schedule.

Highway 401 in the Greater Toronto Area is the busiest and most congested highway in North America. The segment that was widened carries approximately 180,000 vehicles on average per day. Given the built-up area of the Greater Toronto Area, the allowable space to widen the highway was limited as the property comes at a high premium.

One of the more challenging aspects of the project was designing the highway to fit in the constrained area, while also incorporating the project requirement of minimizing the use of barrier wall along the corridor. The design team worked from the approach of adjusting the alignment as best possible to not have any barrier wall on the outside lanes of the widened highway. From there, the constraints were brought in to identify areas where there was not enough ROW available to achieve this. The easy solution would be to use retaining walls and barrier walls wherever this is not achievable. However, this would result in a higher construction cost and introduce additional barriers that are also hazards.

A series of explicit road safety analyses were done to analyze the other alternatives, rather than following the basic design standard concept of adding barrier wall. This included comparing alternatives such as providing a narrower shoulder, reducing lane widths, steepening the roadside slope, using other protection methods for the hazards or other mitigation measures, to determine the option that would have the least societal cost. This resulted in various approaches at different areas throughout the 18 km which ultimately improved the overall safety of the highway by reducing the amount of barrier walls and energy attenuators required.

This concept was also used post-construction to review situations that although they are compliant with the design standard, have a perceived safety concern when reviewed by the road safety auditor, to further determine the best alternative for the area.