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Road Talk



Ontario's Transportation Technology Transfer Digest — Summer 2009 — Vol. 15, Issue 3

Content

  1. Quantm Route Selection: No Stone Left Unturned
  2. Water Blasting Trial Demonstration on a Stone Mastic Asphalt Surface Course
  3. Sustainable Pavements
  4. Moving Towards Pavement Sustainability: CPATT/MTO Sustainable Pavement Workshop
  5. Turning Orange: Construction Zones in Ontario
  6. The Next Generation: Performance-Based Area Maintenence Contracts
  7. Catch me if you can! Longest Rock Fall Catch-Fence in Canada
  8. Building Bridges, Preserving History: Highway 400 Bridge Replacement

Quantm Route Selection: No Stone Left Unturned

Possible corridors generated by the optimization engine.

Possible corridors generated by the optimization engine.

Abrupt rock faces made route alignment more complex.

Proximity to the Mississagi River and abrupt rock faces made route alignment more complex.

The Ministry of Transportation’s (MTO) pilot of the Quantm route optimisation system on Highway 129 in north-eastern Ontario last year has shown that it is possible to optimise land route selection effectively under ecological, geographical, societal and economical constraints with technological aid. Road planning typically involves hand-drawn routes on topographical maps. An engineer’s ability and experience is depended upon to produce the most favourable course through terrain, but this process is often slow and tedious.

MTO tested Quantm, a model-based optimisation tool which generates potential route options by integrating the selection criteria arising from various road planning requirements. Options are narrowed as more criteria are defined. Quantm searches for low-cost routes that best satisfy the selection criteria.

The system was developed by Australian government agency CSIRO for road and railway route selection. Quantm was primarily used for railway route optimization, but has since been updated to allow geographic information systems (GIS) & Computer-aided design (CAD) maps to be read by the optimization engine. The increased flexibility is more practical for non-railway route optimization projects.

The program collects the digital terrain data into a database and analyzes the data through its custom Digital Elevation Model (DEM). Front-end software is installed onto a user’s computer and the data is loaded both onto the software and Quantm’s optimisation engine. The optimisation engine carries out encrypted data transmissions between the user’s computer by way of the Internet. This arrangement eliminates the cost of setting up the IT infrastructure required to support the optimisation engine.

Northeast Region’s Highway 129, 20 km long project was the first project in Ontario to use Quantm in a route planning procedure. The isolated location and the geographical limitations offered a good platform in which to test the software. Abrupt rock faces and the Mississagi River increased the levels of complexity in planning for a 20 km corridor realignment through the Algoma region. The hilly terrain made manual collection of data problematic as the area is difficult to access. One objective was to balance public concerns with the preservation of the scenic view of the river, which was an attraction to tourists passing by the area. MTO turned to Quantm and its unique capacities to render route options with a limited amount of information to locate a route that would strike the ideal balance between feasibility and environmental considerations.

Optimisation was carried out in two parts: one for corridors and one for routes. First, alternative corridors were generated and feedback sought at a Public Information Centre (PIC).  Then the team used Quantm’s optimisation engine to generate a more meticulous combing for route options, along with more reliable cost measurements. The results were presented at a second PIC. Finally, the preliminary design was completed using traditional CAD methods.

The Quantm software successfully complemented the project’s planning process. Overall, Quantm’s most effective feature in this application was that it enabled MTO to explore route corridors under numerous parameters and the benefits of each alternative.

“The program allowed us to ensure that no stone was left unturned in the examination of new route options,” said Ron Turcotte, project engineer of the Highway 129 project.

For more information, please contact:

  • Ron Turcotte, Project Engineer, Planning & Environmental, Northeastern Region, at (705) 497-6945.

Hydro Blasting Trial Demonstration on a Stone Mastic Asphalt Surface Course

Close-up view of the water jets.

Close-up view of the water jets.

Close-up view before (left) and after (right) water blasting.

Close-up view before (left) and after (right) water blasting. Note the excess asphalt film thickness on the pavement surface has been removed.

Stone Mastic Asphalt (SMA), a rut resistant and durable asphalt surface course mix, was adopted by MTO in 2000 as a premium asphalt pavement surface. SMA has since been used in Ontario on major highways with vehicle loads exceeding three million Equivalent Single Axle Loadings per year.  Under these loads, its advantages include; good durability over time, increased service life, and reduced noise, an important design consideration in an urban freeway environment.

The essential features of the mix are its gap graded coarse aggregate skeleton and mastic composition. SMA’s resistance to rut deformation stems from the coarse aggregate skeleton that provides more stone-on-stone contact than conventional dense graded asphalt mixes. The mastic characteristics of SMA incorporate a higher asphalt cement content, which improves binder durability, and a small quantity of cellulose or mineral fibres to help prevent drainage of bitumen during hauling and placement of the mix.

While the properties of SMA are excellent, MTO has experienced early age, lower skid resistance that improves with time and with traffic. This problem has also been reported in the U.S.A, Europe and Australia. The initial friction value is being influenced by the high asphalt mortar content and thick asphalt film which masks the micro-texture of protruding aggregates on the pavement surface.

MTO has been investigating methods to improve the initial friction of SMA.  A joint MTO/Industry Task Group has been focusing on SMA mix design, construction, and treatment to determine potential solutions.  The group, which  includes representatives from the ministry, Ontario Hot Mix Producers Association, AECON, Lafarge, DBA Engineering, and Miller Paving, has researched various re-texturization technologies that could be used to specifically address the early life skid resistance of SMA including:sand grit application, diamond grinding, shot blasting, and water blasting of a new SMA surface.

Water blasting for the friction treatment trial was selected because it is less aggressive, more economical, faster, and more aesthetically pleasing than the others.  MTO partnered with Hi-Lite Canada, a Canadian company based in Kingston, Ontario to water blast 2.3 kilometres of new SMA in the eastbound lanes of Highway 401 in Oshawa from east of Park Road to Bloor Street in October of 2008.

For result comparisons, a pre-water blast friction survey at the posted speed of 100 km/h (FN 100) was performed in September, before the trial. MTO performed follow-up friction surveys of the water blasted SMA immediately after the trial and again in April, 2009. The friction survey data revealed that water blasting substantially increased the friction value by about 20% in all 3 lanes tested.  The April 2009 friction survey data confirmed that these improved friction values were maintained. Further friction surveying will be performed in fall 2009 and annually thereafter to continue assessing the longevity of the water blasting treatment on SMA.

The Task Group has concluded that the water blasting trial was successful and had no negative affect on the integrity or aesthetics of the pavement surface. The operation works well under simple freeway lane closures and is faster and considerably less expensive when compared to other re-texturization methods. Upon completion of this trial, the pavement surface was power broomed to remove a minor amount of asphalt material remaining from the treatment and is recommended for future work of this nature.

Water blasting requires a large water source. On this trial, 47,000 litres of hydrant water was used; 180 litres blasted 40 metres per minute at 4.5 litres per metre. Hi-Lite Canada was able to work within the lane closure and traffic protection requirements and was able to administer the treatment at night to reduce traffic disruption.

Initial findings indicate that water blasting appears to be an efficient, and cost effective method to significantly improve early life skid resistance of SMA. A longitudinal friction survey on the same trial stretch will provide an assessment of the sustainability and long term reliability of this treatment.

For more information, please contact:

  • Stephen Lee, Head, Geotechnical Engineering, Central Region, at (416) 235-5438.

Sustainable Pavements

CIR operation in action.

CIR operation in action.

CIR construction train and equipment.

CIR construction train and equipment.

Over the years, MTO has developed several “green” initiatives to reduce its ecological footprint and promote more environmentally friendly methods of highway maintenance and repair. Examples include: in-place recycling of existing roadway materials, full-scale in-place pavement recycling, and incorporation of alternative recycled materials into the roadway.

Since 1989, MTO has used Cold In-place Recycling (CIR) as an alternative to traditional road maintenance treatments. CIR works by recycling the original hot mix already in place, grinding up the existing pavement, adding a small amount of emulsion and placing the mix back on the road. As a result, CIR saves on asphalt cement, aggregates, trucking and conserves energy. By reusing existing materials, and because the process does not require heat, CIR uses 80% less energy and generates significantly less greenhouse gases than conventional hot mix asphalt.

One of the challenges of CIR is that the construction season is relatively short, as the method requires warm, dry weather in order for the emulsion to set. Ontario’s climate provides only a small window of ideal conditions. As a result, MTO has been specifying a new technology which uses expanded asphalt instead of emulsion. This new method, called Cold In-place Recycling with Expanded Asphalt Mix (CIREAM), adds expanded asphalt to the milled pavement rather than emulsion. CIREAM is less dependent on hot, dry weather than CIR and allows for a longer construction period.

An MTO case study has shown that the use of either CIR or CIREAM in place of conventional road paving techniques reduces greenhouse gas emissions dramatically. The case study compared in-place recycling to traditional mill and overlay treatments. CO­2, NOx, SO2 were reduced by 52%, 54% and 61% respectively. Overall, CIR and CIREAM emits approximately 50% less greenhouse gases per two-lane kilometre. In-place recycling also consumes 62% less aggregates. Additionally, the methods have been shown to be more economical, reducing costs by 40-50% in comparison to the mill and overlay treatments. Where mill and overlay techniques only serve to temporarily suppress cracks within a damaged pavement, CIR/CIREAM mitigates cracks from reflecting to the surface.

In addition to in-place pavement recycling, MTO has been using other innovative strategies of reusing industrial by-products in the pavement structure. Fly ash, silica fume and fine-powdered furnace slag have been incorporated into concrete mixes in place of Portland cement since the 1980s; reclaimed concrete and asphalt pavement, crushed glass, ceramics, and blast furnace slag have been used in granular bases and sub-bases; and roof shingles may now partially substitute for asphalt cement and aggregates in hot mix asphalt. Even with these substitutions, pavements constructed from the greener mixtures are expected to have the same lifespan and quality of conventional paving.

Other pavement greening initiatives include:

  • Long-life/perpetual pavements - thicker asphalt pavements designed with a rich bottom layer to reduce fatigue cracking, with no major reconstruction required over a 50 year period.
  • Warm mix asphalt - mixed and placed at lower temperatures than conventional hot mix, reducing plant GHG and particulate emissions by 35%-60%.
  • Quiet pavements – to address noise concerns in sensitive areas.
  • Pervious pavements – to reduce runoff and promote groundwater recharge (considered a storm water management best practice).
  • Low VOC pavement markings – to reduce GHG emissions.

MTO will continue to refine its green approach through the integration of an environmental component into Life Cycle Costing models. MTO is also developing a “green rating system” that will promote the design, and construction of greener pavements.  The rating system will be based on the innovative sustainable pavement technologies and resource usage. MTO recognizes the importance of environmental stewardship and will continue to pursue greener initiatives for environmental conservation.

For related articles, please see the Winter 2006 issue of Road Talk.

For more information, please contact:

  • Becca Lane, Head of Pavements & Foundations, Pavements & Foundations Sections, at (416)256-4052.

 


Moving Towards Pavements Sustainability: CPATT/ MTO Sustainable Pavement Workshop

Susan Tighe presenting at the CPATT/MTO Sustainable Pavements workshop in December.

Susan Tighe presenting at the CPATT/MTO Sustainable Pavements workshop in December.

The Ministry of Transportation (MTO) is aiming to be a North American leader in adopting a more environmentally friendly approach to pavements. Over the years, the ministry has been working steadily to create more sustainable pavements through in-place recycling, recycling of industrial by-products, warm asphalt mixes, pervious pavements, and perpetual pavements.

The Ministry has also been promoting pavement sustainability and putting it into practice through various incentives, such as: developing a green component to incorporate into Life Cycle Costing Analysis (LCCA), investing in “green” Research and Development (R&D) innovations, providing education and knowledge for the industry, and setting clear expectations for quantities of recyclable material, emissions and energy reductions.

In December 2008, MTO and the University of Waterloo (Center for Pavement and Transportation Technology - CPATT) hosted a half-day Sustainable Pavement Workshop funded by the Ministry’s Highway Infrastructure Innovation Funding Program. The primary objective of the workshop was to bring together a small group of stakeholders to brainstorm how sustainability can be incorporated into pavement engineering and management. The goal was to identify a list of promising innovations and how they can be realistically evaluated and incorporated into pavement engineering practice.

A total of 44 individuals, including MTO staff, consultants, contractors, material suppliers, and the University of Waterloo participated in the workshop and were pre-assigned into six groups based on their expertise. Each of the six groups (Concrete Materials, Asphalt Materials, Design Processes, New Construction / Reconstruction, Preservation Strategies, and Rehabilitation) tackled issues relating to pavement materials, design, tools and processes, which resulted in the examination of the following ideas:

  • More Research & Development, Education and Training
  • More Long Life Pavements
  • Reduction in Greenhouse Gas (GHG) emissions
  • Life cycle costing analyses
  • Energy savings
  • Testing and monitoring of materials and performance
  • Greater use of recycling and in-place recycling
  • Overcoming resistance to change
  • Allowing innovation in specifications

This workshop fostered an opportunity for the participants to understand the need for quantifying pavement sustainability. While there is currently no officially established mechanism to quantify the impact of environmentally friendly materials, procedures and designs, the workshop was fruitful in beginning to formally evaluate the incorporation of sustainability into the pavement design and management process. 

MTO’s next step is to quantify and incorporate sustainability into pavement design and management by developing a “green component” to the LCCA to encourage pavement sustainability in the pavement design stage. Another task would be to review and modify existing specifications to encourage greater use of recycled materials in pavement design and construction.

Watch future issues of Road Talk for articles featuring pavement design and specification updates.

For more information, please contact:

  • Susanne Chan, Pavement Design Engineer, Pavements & Foundations Section, at (416) 235-5509.


Turning Orange: Construction Zones in Ontario

Temporary orange work zone pavement markings.

Temporary orange work zone markings on a test deck in an existing construction project on Highway 427 South at the Gardiner Expressway / QEW interchange in Mississauga.

The Ministry of Transportation (MTO) enforces safety in construction zones by requiring contractors to inform road users of construction with visual signals: signing, lane striping, raised lane markers, painted symbols, and messages on the road surface. With these safety measures, driver confusion may still arise due to scarred pavement from previous marking removal and remaining traces of old markings. In response to this, MTO has been looking to other highway agencies and countries for additional visual solutions to improve road safety during construction.

For some time, the Netherlands and Germany have been using temporary, special coloured, pavement markings to help guide traffic through construction areas. Similarly, MTO is adopting the use of temporary special coloured markings to minimize the probability of driver confusion while approaching, driving through, and exiting a construction zone. MTO is also taking this idea a step further by choosing fluorescent orange pavement markings to provide colour correlation with the existing orange, visual construction signs and barrels in Ontario construction zones.  MTO is restricting this new tool to alignment changes in construction zones on divided multilane roadways only. This construction season, the orange construction zone pavement markings can be seen on Highways 427, QEW, and 409, where they have received many positive reactions from road users.

The use of temporary fluorescent orange pavement markings is relatively new, and MTO has been investigating different materials to use. In fall 2006, MTO tested orange organic solvent-based paint on Highway 401, and a two-coat waterborne paint system on Highway 406, both of which improved visibility. In August 2007, MTO tested the application of fluorescent orange methylmethacrylate (MMA) on Highway 427. Observations of this application yielded many positive results, as well as improved visibility, substantiating it as an ideal marking material.

MMA is an organic compound and provides improved visibility and durability compared to the other pavement marking materials tested.  MMA has very good adherence to milled asphalt and to concrete pavement surfaces. Its properties allow for successful application in low temperatures which can be problematic for other materials.  MMA has also shown good retention of the glass beads which are imbedded in the surface of pavement markings, especially important for night time visibility.

Temporary orange pavement markings provide MTO and its contractors with an additional aide for reducing potential driver confusion within construction zones. MTO is working to make this new tool a standard in construction zones. MMA appears to be a suitable and cost effective application for fluorescent orange that satisfies visibility and durability requirements for channelling and guiding traffic in an orderly and safe stream through construction.

For more information, please contact:

  • Grant Ridley, Chemical Engineer, Materials Engineering & Research Office, Highway Standards Branch, at (416) 235-3728
  • Dave Edwards, Senior Project Manager, Traffic Office, Highway Standards Branch, at (905) 704-2929
  • Vic Ozymtchak, Maintenance Officer, Maintenance Standards Section, Highway Standards Branch, at (905) 704-2649

The Next Generation: Performance-Based Area Maintenence Contracts

Contractor work

Contractors conducting winter maintenence on a ministry freeway

In March 2009, the Ministry of Transportation (MTO) awarded the first Performance-Based Area Maintenance Contract (AMC) in the York contract area, north of Toronto. This new generation of AMCs features three significant changes to the previous AMCs. First, the new AMC is a ‘one window approach’, which assigns maintenance, low complexity capital improvements, and data gathering to a single contractor covering a specific geographic area over several years. Second, the new AMCs focus on performance-based requirements with result-based oversight by MTO. Third, contractors are required to acquire and maintain ISO certification as a condition of the contract.

One-window approach
Previously, MTO contracted highway maintenance, capital work (low complexity) and the gathering of highway-related data (e.g. traffic or pavement) separately. In the new AMCs, MTO is using a single service provider to deliver a bundle of services instead of contracting separate tasks to multiple service providers. This ‘one window approach’ was developed to ensure more efficient services and better pricing by grouping tasks of low complexity capital work and data gathering to the contractor who is already working in and familiar with the area. The Third Generation AMC contractors will perform low complexity capital work assigned by MTO as well as work that they propose in extra work reports, once approved by MTO. More complex capital work will continue to be identified and contracted separately from AMCs.

Performance-based requirements
Until now, previous generations of AMCs were prescriptive and method-based, and used labour-intensive, time-based oversight methods for monitoring contract compliance. The new generation of AMCs is performance-based; contractors deliver to outcome targets which MTO monitors through results-based oversight. Key performance requirements unique to the third generation of AMCs describe the outcome target indicators and consequences of non-compliance concerning each task. Results-based oversight is intended to hold contractors accountable to their tasks, allow for contractor innovation, and assure quality with less labour-intensive supervision from MTO.  

Contract compliance of both maintenance and low complexity capital work will be monitored through standard province-wide performance requirements for consistency and through region-specific contract requirements that address the particular needs of an area.

ISO-certification
Third Generation AMC contractors are required to be ISO-certified and must meet ISO standards for quality management system and environmental management system. The ISO -International Organization of Standardization – sets and monitors international quality standards for best business practices. ISO-certification is intended to assure that the new AMC contractors meet internationally recognized quality business standards and are subject to independent, third-party audits.

The Third Generation of AMCs will supplement MTO’s suite of contract delivery models and provide the ministry with additional flexibility in tailoring contracts to specific areas.  New contract models provide an environment for contractors to be innovative and meet the performance requirements of ministry contracts.

For more information, please contact:

  • Mike Houle, Senior Maintenance Contracts Officer, Maintenance Contracts Section, at (519) 873-4218
  • Jeff Baker, Head, Maintenance Contracts Section, Contracts Management Office, at (905) 704-2628

Catch me if you can! Longest Rock Fall Catch-Fence in Canada

Installation of the Kama Hill rockfall catch fence

Installation of the Kama Hill rockfall catch fence

completed rockfall catch fence

Completed 221m rockfall catch fence

Catch fence installed at Kama Hill

Although difficult to see in this picture, the high energy catch fence was installed in Kama Hill along the Rossport formation approximately 15m above the TransCanada Highway, 12m east of the Highway 11 and Highway 17 intersection in Nipigon.

Along the TransCanada Highway, east of Nipigon, Ontario, bluffs of Precambrian rock rise more than 200m above Lake Superior. These bluffs are made up of eroded remnants of thick rock “sills” which have a high rockfall potential. At Kama Hill near Nipigon, rockfalls occur as a result of loose rock falling from cliffs that are over 100m above the highway. The increased chance of rock-vehicle collisions as well as rock debris on the road is a safety concern. In the past, rocks have bounced and tumbled down the steep slopes from high above and landed on and across the highway. To prevent future incidents of this kind, the Ministry of Transportation has installed the longest high energy rockfall catch fence of its kind in Canada.

Rockfalls occur when isolated rock blocks are able to slide or roll from their original location and fall under gravity. At Kama Hill, two specific rock formations along the TransCanada Highway are particularly susceptible to rockfalls: the Rossport Formation and the massive diabase sills of the Upper Keweenawan Supergroup. The Rossport Formation is located close to the highway and consists of a bedded and blocky, red, medium-grained, medium-strong, moderately weathered rock mass. The Upper Keweenawan Supergroup sills are located high above the highway and consist of a grey, very strong, coarse-grained, columnar rock mass.

In 2003, MTO contracted David F. Wood Consulting Ltd. to investigate and assess the area for rockfall potential and design a remediation system to address the rockfall potential. The consultant reviewed the slope, materials, rock conditions, rockfall activity, and long term stability of the escarpment. By helicopter inspection, the consultant assessed the Kama Hill area as high risk because of the unusual rock formation conditions compared to other areas in the Northwestern Ontario Precambrian Canadian Shield.  During the assessment, the consultant determined the source of two past rockfalls, but more importantly, the locations of potentially unstable blocks and wedges still present.

Along with the helicopter investigation, historical reports and computer software were used to design the installation parameters of the catch fence. Using a software package distributed by RocScience Inc. called RocFall, the consultant conducted a risk analysis of falling rocks from the areas of concern. RocFall simulated actual rockfalls from high risk areas and calculated the area of lowest velocity for the falling rocks, which was found to be at the crest of the Rossport Formation slope just above the highway. A catch fence is ideal in this location, where falling rocks have lost most of their energy, reducing the energy impact on the catch fence.

Following this investigation, MTO competitively tendered and awarded a contract to Pacific Blasting and Demolition Ltd. to install the high energy rockfall catchment fence in the designated location. The contractors also removed any unsound rock above the fence location using labourers, explosives and equipment to ensure the work area was safe prior to the fence installation. This unique catch fence, made by Trumer Schutzbauten and imported from Austria, comes pre-assembled as a rolled up fence with anchors for easy installation. The steel fence is woven into a net which provides energy absorption by stretching upon rock impact. Hot dip galvanization protects the fence from corrosion. The fence anchors are fixed into existing rock and embedded with concrete to provide high strength and flexibility.

Pacific Blasting and Demolition Ltd. began construction on September 4, 2008 and completed the work on October 31, 2008, on time and under budget. The 200m catch fence is capable of successfully ‘catching’ a 10,000 kg block travelling up to 70km/hr. Instead of requiring maintenance and repairs to the entire structure in the event of a rockfall, this cost effective sectioned fence will only require maintenance and repairs to damaged sections. MTO will inspect the fence annually or immediately following a large rockfall event. Upon the first annual inspection, it is expected that the new fence may have already stopped several smaller rocks; thereby, successfully improving road safety on the TransCanada Highway through Thunder Bay.

For more information please contact:

 

Below is a demonstration of a rockfall catchment fence test for the type of fence MTO installed at Kama Hill.

 

To see more demonstrations of a rockfall catchment fence, please visit: http://www.trumerschutzbauten.com/ .

Videos courtesy of Trumer Schutzbauten with permission


Building Bridges, Preserving History: Highway 400 Heritage Bridge Replacement

Highway 400 Bridge to be replaced

This is an example of one of the Highway 400 underpasses to be replaced

concept 1 best integrates the recommended design elements and preserves aesthetics and heritage value along the corridor. However, this concept is not feasible within the Barrie city limits on Highway 400 since its 3.5 m girder depth would require significant changes to the profile of the approaches.

Concept 1

concept 2 has a shallower girder depth, but because it is a constant depth two-span bridge, it is not very sympathetic to the original bridges.

Concept 2

concept 3 is a better sympathetic design than Concept 2.  It retains the variable depth girders as a two-span bridge and it has a shallow girder depth which makes it feasible for areas within the Barrie city limits.

Concept 3

Ontario Coat of Arms

An 1800mm x 1625mm, reusable, urethane mould of the provincial coat-of-arms has been created from the Highway 400/5th Line structure, south of Bradford.  The mould will be owned by MTO and will provide the Ministry with a durable, high quality product that can survive multiple pours over many years.   The intent is that the mould will be reused for all of the replacement underpasses along the Highway 400 corridor within the study area with concrete castings to be installed in all four quadrants of each new bridge.

Highway 400 is home to some of the first freeway underpass bridges ever built in Ontario. Built between the late 1940s and mid-1960s, these bridges are considered to be historically significant because they are among the only bridges in the province which represent the provincial highway engineering and architectural practices of their time.  The planned widening of the Highway 400 corridor from six to ten lanes between the Greater Toronto Area and Barrie means that the sixteen underpasses along the 60 km corridor between Major Mackenzie Drive in the City of Vaughan and the junction with Highway 11 at Crown Hill will need to be replaced. The widening between Major Mackenzie Drive and King Road is planned to commence by 2011. Considering their cultural and heritage value, the Ministry of Transportation investigated methods of incorporating the aesthetically and historically significant features of the existing sixteen bridges into the design of the replacement underpasses. This will preserve their heritage value and maintain aesthetic unity along the corridor.

This study was conducted by a team of consultants, including SNC Lavalin Inc. in association with Paul Gauvreau, a bridge aesthetics specialist, and Unterman McPhail Associates, cultural heritage specialists. They followed a systematic development process to identify the design concepts for the replacement bridges, which included the following steps:

  • A review of relevant documents to become familiar with the existing bridges along Highway 400 and the preliminary design proposals for their replacement
  • Reconnaissance of the existing bridge sites to gain first-hand impressions of the visual features and their broader cultural context
  • Identification of common historical and aesthetic design elements of the existing bridges to define the criteria for selecting which elements to carry forward in developing the new bridge design concepts
  • Development of three alternative design concepts and the assessment of those concepts against sympathetic design criteria (i.e. suitable recognition of the historical and aesthetic character of the original bridges), constructability (staging), cost and maintenance requirements

The study recommended that the following design elements from the existing underpasses be incorporated into the new replacement bridges:

  • Design the bridges with a high degree of visual consistency, which recognizes the diversity of the functional requirements and contexts along the corridor.
  • Design the bridges of the Highway 400 corridor in concrete.
  • Develop at least one single-span post-tensioned concrete rigid frame design concept adaptable to as wide a range of functional requirements as possible.
  • Use variable depth superstructures unless prevented by clearance constraints or the cost premium is excessive.
  • Keep non-structural adornment to a minimum.
  • Use structural systems and details that offer freedom to define the shape of primary structural elements.
  • Incorporate state-of-the-art technologies, which contribute positively to the finished product or enable the implementation of other recommendations made.
  • Use crash-tested open railing systems.
  • Include the provincial coat of arms.

Based on the functional requirements of the proposed Highway 400 improvements and the recommended retention of the above noted design elements from the existing underpass structures, the following three sympathetic bridge design concepts were subsequently developed for the replacement structures.

Concept 1
The first concept is a single span (70m) post-tensioned concrete rigid frame bridge with the depth of girder varying from 1.4m at mid-span to 3.5m at the ends. The girder cross-section features a single-cell box girder with wide deck slab cantilevers that enhance the visual slenderness of the girder by creating a pronounced shadow line.

Concept 2
The second design is a two-span post-tensioned concrete girder bridge. Each span is 42.5m in length with a constant girder depth of 1.8m. The corresponding span to depth ratio is 23.1.  The girder cross-section is also a single-cell box girder.

Concept 3
The third design concept is a two-span post-tensioned concrete rigid frame bridge with variable girder depth. Each span is 35m in length and varies in depth from a 0.7m at mid-span to 1.75m at the ends. The corresponding span to depth ratios are 50:1 at mid-span and 20:1 at the ends. The girder cross-section is a single-cell box girder near the ends of the span and a solid slab near mid-span.

Evaluation of Design Concepts
All three design concepts were evaluated based on their effective integration of the recommended heritage elements, construction staging, construction cost, and maintenance requirements with the results summarized below:

  • Concept 1 best integrates the recommended design elements and preserves aesthetics and heritage value along the corridor. However, this concept is not feasible within the Barrie city limits on Highway 400 where a 3.5 m girder depth would require significant changes to the profile of the approaches.
  • Concept 2 has a shallower girder depth, but because it is a constant depth two-span bridge, it is not very sympathetic to the original bridges.
  • Concept 3 is a better sympathetic design than Concept 2.  It retains the variable depth girders as a two-span bridge and it has a shallow girder depth which makes it feasible for areas within the Barrie city limits.

All three concepts are reasonably cost effective.  Relative to a CPCI (pre-cast concrete) girder structure, the premium ranges from 4 to 58 percent.  The cost premium for Concepts 1, 2 or 3 were considered to be reasonable, given the significant benefits from their incorporation of the recommended heritage design elements. 
Concept 1 appears to capture the recommended design elements to best preserve heritage value and uniformity of the underpass bridges.  It is therefore recommended as the preferred design for the replacement underpass structures along the Highway 400 corridor except in constrained areas, such as the City of Barrie, where its girder depth is too large. In those areas, Concept 3 is recommended because of its aesthetic value combined with a shallower girder depth.

To further enhance the sympathetic design of the replacement bridges, the provincial coat of arms will be incorporated into the wing walls of the bridge abutments. In 1909, Premier James P. Whitney introduced the coat of arms as Ontario’s main identifier until the introduction of the stylized trillium in 1964. Built before 1964, the bridges on Highway 400 are among the only remaining structures in Ontario that bear the coat of arms. Incorporating the coat of arms into the design of the replacement structures is a feasible way of retaining a significant sympathetic element and the cultural value of the original bridges.

These efforts recognize the engineering heritage of our province.  The Ministry of Culture and heritage enthusiasts are strongly supportive of this initiative.

For more information please contact:

  • Heather Glass, Senior Project Engineer, Planning and Design, Engineering Office, Central Region at (416) 235-5521.


Reader Response


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By Email:
kristin.macintosh@ontario.ca
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Ontario Ministry of Transportation
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