Highway construction question.

[XamotCGC]

How exactly is a four lane highway widened into a five lane highway, with the fifth lane being a turning lane in a dense commerical area?

I drew a crude sketch of what I'm trying to ask, but wasn't sure how to post it.

[Scott5114]

The exact details depend on the highway's surroundings, the type of pavement being used, location of utilities, amount of right-of-way available etc. No two construction projects are the same.

How to include an image in a post

[bwana39]

How exactly is a four lane highway widened into a five lane highway, with the fifth lane being a turning lane in a dense commerical area?

I drew a crude sketch of what I'm trying to ask, but wasn't sure how to post it.

Are you talking about in the EXACT footprint or as space economically as possible? 

Using the exact footprint, a common way would be to use a combination of using any existing shoulders and / or median then perhaps trim the lane width.  Four twelve foot lanes with  one foot  margins outside the lanes could be converted into four 10-foot lanes and a 10 foot center turn lane.

If you had additional room, you could do it several ways.

[Dirt Roads]

How exactly is a four lane highway widened into a five lane highway, with the fifth lane being a turning lane in a dense commerical area?

I drew a crude sketch of what I'm trying to ask, but wasn't sure how to post it.

We do this on the railroad all the time, but very few railroads and rail transit corridors are four tracks wide anymore.  You need to start with a three-dimensional image.  Simply put, the first two dimensions look like a map, but the third dimension is represented with a bunch of cross-sections (perpendicular to the roadway centerline) showing the width the roadway and the elevations of the existing pavement, subgrade (sometimes presumed), drainage, local terrain and other important stuff.  Depending on how "long" the project is, you might get cross-sections every 25 feet or every 50 feet.  On my rail projects, I also wanted to see a detailed cross-section everywhere the terrain changes (those usually get thrown out later).

I've seen some civil engineers go out on a limb and try to work off of the basemap first and then get a feel for whether their preliminary design works with cross-sections.  But the best designers wait for the cross-sections and make adjustments based on how far the proposed changes impact the right-of-way.  A lot of this depends on the hydrology (water drainage):

• four lanes of pavement in the tangent (straightaway) needs a middle crown for drainage onto both sides
• four lanes of pavement in curves needs superelevation for curve speed, which forces all drainage onto one side
• the transition between a middle crown and a superelevated curve needs to be smoothed out, if possible
• the drainage ditch or storm sewer needs to get deeper and wider the further you go downhill
• the maximum slope that you create should be no more that 2:1; if you must go more than that you'd better plan on a retaining wall

You basically take each cross-section and try to squeeze in all of the needed changes.  Then you go back to map and tie them together and smooth things out with professional curves and spirals.  Once you are satisfied that everything fits in three dimensions, then you need to go create an elevation map (elevations versus the longitudinal coordinates).  That will show the existing elevation versus the proposed elevation (on the railroad, we sometimes need a separate elevation chart for each track).  All of the vertical curves need to be smoothed out, which sometimes results in changes to the alignment and the cross-sections.  Larger companies have software that will do most of this work, but I've worked on projects that we had to almost all of this by hand.  I find it to be a lot of fun, and I could get extremely accurate cost estimates from being intricately involved with the design effort. 

From this, you can calculate the area and volume of everything.  Civil engineers think in terms of the amount of earthworks (cut, fill and borrow).  On huge projects, the designers will run what-if scenarios in an attempt to minimize the amounts of cut and fill.  In the bigger picture, they are also trying to minimize the costs of bridges, retained cuts and retained fills.

I'm assuming that you asked because you are interested.  I like to teach others to think in three dimensions.  Go out and dream up a simple project.  Step-by-step, make simple maps and sketches and do the math yourself.  Don't worry about being perfect.  Then go back and play with your five-lane scenario.  (If you want to consider a career in highway design or railroad engineering, go spend a lot of time getting into the meat of all of the details.  Otherwise, just go and have fun playing in three dimensions).

[XamotCGC]

https://www.google.com/maps/@37.5602045,-85.271099,3a,75y,215.77h,78.22t/data=!3m7!1e1!3m5!1s3vV6moQrm1OQpHjU9Buq2Q!2e0!5s20130501T000000!7i13312!8i6656

This google map link is a perfect example of a four lane highway  that became a five lane highway with a turning lane.  Not sure when it was done. (Would love to find out.) 

[Dirt Roads]

https://www.google.com/maps/@37.5602045,-85.271099,3a,75y,215.77h,78.22t/data=!3m7!1e1!3m5!1s3vV6moQrm1OQpHjU9Buq2Q!2e0!5s20130501T000000!7i13312!8i6656

This google map link is a perfect example of a four lane highway  that became a five lane highway with a turning lane.  Not sure when it was done. (Would love to find out.)

Wow, look at the flatlands.  Not much in the way of reconstructing a four-lane road into a five-lane road (four-lane road plus the "chicken lane").  The big issue here would have been to determine which side of the highway required the most expensive utility relocations (and then push the alignment towards the other side, if needed).  The centerline of that alignment looks so smooth that KTC probably didn't even worry about the utility relocation costs when they widened here.

[jeffandnicole]

How exactly is a four lane highway widened into a five lane highway, with the fifth lane being a turning lane in a dense commerical area?

I drew a crude sketch of what I'm trying to ask, but wasn't sure how to post it.

You can post a GSV line to where you are talking about, which would help.

However, in general, they could widen a roadway to 5 lanes by removing (or reducing the width of) the shoulders, by widening to one side, by widening to both sides, or any combination thereof. If the sidewalks go right up to the roadway, they can reduce the width of these sidewalks. Or cut out parallel parking if it exists.

It's not unusual for a roadway to have the right-of-way already set for such a widening. It may not be fully apparent to us everyday people, but when businesses built their parking lots and access points and drainage, and when power companies put in their poles, property boundaries are usually well marked put on plans.

[Tom958]

Here's one. I'm told that people eventually got used to it. Per Google Maps, the pavement width is about fifty feet. https://goo.gl/maps/iTQTiiVsSV546ZMQ7