I believe all but 2 overpasses between Tilbury and London can support 6-lanes without any modifications or replacement work.
Funny enough these two already have the concrete median, but it would make little sense to keep these 4-lanes since the 6-lane stretch east of the 402 is just a few kms away
Location of both:
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The horribly obsolete cloverleaf at Highway 4 could have all of its loop ramps removed to squeeze in a third lane.
-This is how several interchanges were reconfigured when the 401 was widened between the 402 and 403
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This overpass would have to go bye-bye however. Farmers nearby are delaying it's demoliton until they have assurance it will be replaced.
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Of course any bridges on the 401 itself would need to a third span in the middle to join the two existing ones. This one going over a now non-existent rail line could be removed however.
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