For example, how do engineers create 6+ lanes where there were only 4 before? How are they able to create additional lanes when there are solid structures that exist close to where the old lanes were?
In: Engineering
They don’t. They buy those homes and businesses and bulldoze those buildings to make room for the extra lanes. It’s called eminent domain. The government has the right to buy those buildings at any time and the owners are forced to sell them in order to make room for a Public good.
Unless they’re going to buy up the surrounding land and bulldoze it. All they can do is just try to squeeze in more lanes where they have space
Extra space can come from removing parking spots along the road, or shrinking the sidewalks. Or removing things like bike lanes.
But really if they aren’t really making any physical changes to the road, they’re just shrinking the actual width of each lane. For example a 60 ft wide road might have 4 15ft lanes. If they wanted they could squeeze that to 5 12ft lanes. (12 ft is the typical width of highway lanes). In some extreme cases like dense urban areas lanes can get shrunk even further to 10ft, possibly under special circumstances (with city council aprroval) to even smaller, but that generally comes with rules like banning buses/trucks from using that road.
A lot of roads were originally built with space in the middle, and breakdown lanes and more space on the outside. That can be converted into additional traffic lanes.
Verges and footway widths can be reduced to make more carriageway widening width. Existing lane widths can be squeezed down to help with this. Any embankment side slopes can be steepened up and possibly even replaced with retaining walls to get more land within the existing highway boundary. More often than not! A combination of all of the above is implemented. The real issue is existing bridges either carrying the road or passing over. Widening these is going to be expensive and often is the reason for widening not to have happened sooner due to lack of funding.
I’m seeing this exact thing where I live in California. Been driving through it for the last 10+ years whilst they do a 10 mile section (lol). If you pay attention, they are actually moving the whole freeway left and right while they add lanes. Seems they find a center and go from there.
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