Project Objectives, Solutions and Achievements
With the VACIS located east of Walker Road, a major north-south artery in the City of Windsor, trains would be required to reduce speed to 7 km/h or less as they passed through the system. The reduced speed, combined with an anticipated rail traffic volume of between 25 and 30 trains within a 24-hour period with train lengths of up to 1.5 kilometres, would translate into approximately 135 minutes in delays to vehicular and pedestrian traffic at the Walker Road level crossing every day, creating enormous traffic interruptions and congestion on both Walker Road and the intersecting Grand Marais Road.
Previous studies by the City of Windsor identified this level crossing as a major obstacle in traffic movement that required a grade separation. The introduction of the VACIS only exacerbated that need and enticed Federal and Provincial Governments to assist with funding for the projectunder the Let’s Get Windsor-Essex Moving strategy, a $300-million investment for several transportation infrastructure projects that would improve efficiency and reduce congestion in Windsor and EssexCounty.
It was at this time that the City of Windsor joined forces with Dillonand a collaboration of other design team members to devise a design approach that would not only address the traffic interruptions on Walker Road and Grand Marais Road and the requirements of the VACIS security facility, but also conquer the numerous design constraints and challenges that would arise. Adjacent Union Gas and Chrysler’s properties, construction of a CPR rail diversion, interferences with overhead Hydro One transmission lines and towers, and a myriad of other existing overhead and buried utilities would all need to be addressed.
The successfulcompletion of theproject required the coordination and cooperation of Federal, Provincial and Municipal levels of government, major utilities Union Gas and Hydro One, and the Canadian Pacific Railway;it eliminatedthe excessive traffic congestion of the previous level crossing, the consequent driver frustrations and environmental impact from idling cars; and it beautified an intersection within an industrial area of Windsor through the use of architecturally aesthetic retaining walls and landscaping enhancements.
Technical Excellence and Innovation
When determininga suitable configuration for the new bridge and associated road and rail works, Dillon needed toascertain the unique set of engineering and coordination challenges specific to this site. Dillonultimately concluded that the use of ballasted through-plate girder spans would be the best and most practical design approach, but not before considering an assortment of issuesand constraints related to the road geometry, rail alignment and utility coordination.
The proposed roadway cross section would require an overall width between bridge abutments of at least 26 metres to allow for two lanes of traffic north and south on Walker Road, a turn lane in each direction from Walker Roadonto Grand Marais Road and sidewalks and bike paths. Taking into account the skewed alignment of Walker Road, the turning movements at the intersections and other specific requirements of CPR would eventually increase the overall bridge span to over 45 metres.The span length would push the feasibility limits of steel through-plate girder configurations, in terms of both flange thickness and practical limitations on girder depth.
The minimum vertical clearance acceptable to CPR would require5 metres from the top of pavement on Walker Road to the underside of the new structure. In order to minimize the depth of the superstructure and in turn limit the depth of excavation below existing grade as well as the length of approaches, girder style bridges with the tracks located on top of the superstructure (deck-plate girders) were eliminated as structure options. The envelope of the path of commercial trucks turning from Grand Marais Road to Walker Road southbound while providing adequate sight visibility would eliminate the opportunity to provide intermediate pier supports for the bridge between the back of sidewalks on each side of Walker Road. Finally, although it provided a viable structure choice for a longer span rail structure, a steel through truss designhad to be ruled out as an optiondue to interferences with the overhead Hydro One transmission lines, an extensive on-site assembly process, and an aesthetically inferior design. The ballasted through-plate girder was the proper choice.
The extent of possible open cut construction at the bridge location would be severely limited due to the close proximity of Union Gas property which contained high pressure gas facilities and Chrysler’s property. In addition, the CPR rail diversion would further impact construction. The temporary diversion would need to be shifted to be sufficiently clear of the new structure site so as to avoid the need for full time flagging during construction, while at the same time limiting the encroachment of the diversion into adjacent Union Gas and Chrysler’s properties. This would result in the extensive use of temporary braced sheet piling retaining walls in order to excavate the necessary 8.5 metres below existing grade level with minimal detriment to the surroundings.
Introduction of the CPR subway would clearly present issues with storm water management around the site, and ultimately affect the Grand Marais Drain to the east of Walker Road. Surface water runoff could no longer be managed by gravity and as such a new pumping station would beessential. The pumping station would not only be required to pump the system from an elevation below Walker Road at its shallowest point up to the much higher elevation of the existing Grand Marais Drain, but also be able to manage a 50-year peak flow generated by the drainage area. Finally,the rail diversion for the CPR tracks around the site would necessitate a new longer culvert for the Grand Marais Drain under the CPR tracks and in turn the realignment of the Grand Marais Drain itself.
Level of Complexity
A considerable number of constraints were present at the Walker Road level crossing, placing substantial limitations on Dillon to incorporate a viable approach to the grade separation design that would meet the project’s objectives.
First and foremost would be the need to maintain uninterrupted rail traffic around the grade separation site during construction. With Union Gas property containing high pressure mains to the southwest and the Chrysler engine plant to the northeast of the site, there were limited opportunities to employ a suitable rail diversion around the site. A rail diversion that would be deemed acceptable would need to comply with Canadian Pacific Railway’s standards for track geometry and switching, allow trains to move through the VACIS facility, limit encroachment onto the adjacent Union Gas property, maintain or exceed the present clearance between the railway track and the Hydro One tower to the northwest (current clearances were substandard), and minimize the extent of any additional work, such as the need to extend the Grand Marais Drain culvert which ran under the railway to the east of Walker Road. Finally, timing for diverting the railway would be affected by weather conditions and the availability of qualified track-laying crews.
Another hurdle would be avoiding interference with Hydro One high voltage overhead transmission lines which crossed diagonally over the site. The potential conflicts between pile driving equipment and energized overhead power cables combined with the fact that the horizontal clearance between the current tower locations and the railway track was already deemed to be less than the current clearance requirements necessitated the relocation of the overhead transmission lines. Thiswould in turn require the construction of two new transmission line towers. In order to accomplish this work, it would be necessary to significantly reduce the power in the conductors during the relocation. However, exceptionally high demand during the summer months would dictate that the work could only be carried out between the end of September and the beginning of March. This would impose a significant impact on the timing and duration of bridge construction.
There would also be present a multitude of both overhead and buried utilities crossing the site that would be directly affected by any excavation or erection equipment. In fact, the first two phases of the project would be dedicated to the relocation of the existing utilities, before any part of the grade separation work could commence. Overhead electrical distribution power lines, telephone, cable and communication utilities would need to be buried within specially constructed duct structures. Existing underground watermains, telephone, cable and communication utilities would all need to be relocated so as to avoid interferences with the new bridge foundation piles. However, special abutment and pile designs would be required around an existing 1500 mm diameter trunk sanitary sewer that would not be relocated, crossing diagonally through site and buried some 13 metres below existing grade (6 metres below the future Walker Road elevation).
In reality, there would almost certainly be few other locations more congested in which to builda new rail bridge, new subway, reconstruct an intersection and construct a new grade separation.
Contributions to Quality of Life
The successful completion of the Walker Road / CPR Grade Separation eliminated a major source of traffic congestion, improved traffic flow and increased commuter safety on a busy arterial roadway while reducing the environmental impacts associated with exhaust and noise pollution from idling vehicles and trains waiting in long delays at the original level crossing.The lowering of Walker Road and Grand Marias Drain Roadalso mitigates the vehicular traffic noise on the residential area without erecting obtrusive noise barriers.
The beautification improvements to the area werealso significant. An architectural “angle step” relief incorporated into the retained soil system walls, combinedwith landscaping and handrail enhancements, created a visually appealing corridor for the public. Medium-size conifers were planted along Chrysler’s property line on top of the retaining walls. Considerations were given to pedestrian, bicycle and vehicular traffic, creating a stark contrast to the largely industrial appearance before construction began.
Although the Grand Marais Drain is situated in the industrial area, the fish population was found to be the most diverse and abundant within the local area. Significant ecological considerations were given to the Grand Marais Drain realignment so as to preserve their natural environment.
The grade separation will yield long term economic benefits in the form of lower transportation costs, reduced costs of operation and maintenance of public and private transportation systems. The grade separation will also increase movement of goods which will support regional job growth.
Owing totheir affiliation with Dillon, either through design or construction, several area suppliers and subcontractors were able to showcase their products and services as they were employed to overcome the intricacies and difficulties in completing this project. The increased exposure of their products and services will translate into future growth for these companies and economic benefits for their employees.