Building a 4-lane highway under existing tracks?

Every time I drive up the fairly new section of Highway 400 south of Parry Sound, Ontario, we go under a railway overpass. I'm pretty sure the tracks are part of an existing right-of-way on the line between Mactier and Parry Sound i.e. the tracks were there before the highway was.

Can anybody tell me how such a construction project could be run? I don't think the rail line could be out of service for more than a day or two, right? So how did they do it?

Thanks for any comments.

Moderator's note: topic moved from CP Rail forum

usual way would be to build a temporary track around the construction area.

There are a few ways of doing it. From looking at Google images in this particular case, http://maps.google.ca/maps?f=q&source=s ... 2&t=h&z=17 and http://maps.google.ca/maps?f=q&source=s ... .2,,0,1.98, it appears that the highway was dug/cut into the rock to just north of the tracks, then a new rail bridge was built into the opening. After the bridge was finished, new track was laid across it and connected to the existing rail line. Once the new alignment was in place, the old rail was removed and the rest of the hole for the highway was completed.

Thanks very much for both replies. I never thought to look at the crossing using Google Earth. When I did this morning, I could see what appears to be the temporary road bed to the south. I'll be going by there this afternoon (on the highway) and I'll be trying to take a closer look. Thanks again!

IDOT did a similar project for the Nashville & Eastern when they widened Briley Parkway. Part of the new route took out some small curves. Briley Parkway is now a 8 lane underneath. There must be some process for the TDOT to plan & buy the new ROW.

It is common practice for a railroad to construct a "shoo-fly" track around a construction site, such as a new highway to be located below the railroad grade. Often resulting in slow orders below the usual track speed due to the curves. NJ Transit did the same last couple or three years while refurbishing some railroad bridges on the Raritan Valley Line. In that case the ex-CNJ was originally a 4 track mainline so the remaining two tracks were diverted to the outer area of the right of way during construction.

There was an interesting spot in Edison on the NEC where they widened an underpass one track at a time since there wasn't room to build a run around...the works looked very tight w/ all the cribbing 'N stuff to keep the tracks in place.