Economies of Scale in Overpass Construction?

[ardecila]

In the metropolitan area where I live, a major railroad is planning to purchase a smaller, lightly-used railroad and vastly increase the number of trains per day on that railroad.

The communities along the line, understandably, oppose the purchase because of concerns over noise, road congestion, and emergency vehicles. However, chances are that the railroad will get their way, so I believe that these communities need to start planning now to address the traffic congestion that they believe will come.

The typical solution for this is a grade-separation - shifting the road over or underneath the tracks, or, more rarely, shifting the tracks above or beneath the road. There are 143 grade crossings along the line, and roughly 40 of them have enough road traffic to warrant grade separations.

Can a streamlined system be set up, involving engineers and contractors, to mass-produce these under/overpasses? The principle of "economies of scale" should be able to reduce costs greatly, and make such a large project (40 grade separations) possible. However, since each site is unique, the savings may not be so great. But it seems like, if we were able to set up engineering firms to design thousands of miles of (completely grade-separated) interstate highway, then this should be possible.

[You Need A Thneed]

You may save in Contractor's Fees by bunching the grade seperations up into one contract, but you would reduce the amount of contractors that could bid on the project, reducing competitiveness. You don't really see economies of scale too much in the price of materials.

[Nowhereman1280]

You will achieve some economies of scale, but nowhere near the econimies already gained from using prefabed parts like the spancrete I-beams they often use achieve. Like Thneed said, there will be a cost reduction if all the contracts are awarded in a lump bid.

[Kelvin]

Yes ... and No. There is a possibility that, if a standard set of details and sections are identified at the outset, some large savings will be realised. The total cost of materials may be higher, but is outweighed in savings due to production speed (fabricators keep mass producing the same few elements over and over), assembly (contractors keep putting the same few pieces together the same way over and over), and mobilization (you keep the same crews and equipment operational continuously).

When that happens - then large projects do offer appreciable "economies of scale". When they don't cost savings are few and far between.

The obvious drawback to cookie-cutter engineering is the lack of variety and visual appeal. In some cases, small enhancements can be made (for relatively small cost) that make large monolithic and repetitive structures seem a little more appealing. For example, if there will be large walls and many piers, each can be fitted with one of a few different formliners that would be unique to the project and give it some harmony and improve appearances. Similarly, colored sealers can be applied so the concrete is not so drab, etc.

[arkhitektor]

The Utah Dept. of Transportation used a related method to replace a number of bridges along I-80 this summer.

Instead of building each new bridge on site, they used a large staging area adjacent to the freeway to build each bridge out of the flow of traffic, thus not affecting traffic on the freeway or cross streets.

Then over the course of a few weekends, they closed the freeway and used a large lift/roller to move all of the bridges in place and set them over the roadway.

http://www.udot.utah.gov/innovate80/

I'm no engineer, but it sounds like it was pretty succesful and saved a lot of time, money and lessened traffic impacts compared to traditional methods.

One of the new bridges being moved into place:

[Kelvin]

This type of structure work is becoming more popular in N.America (have been doing longer in Europe). While the actual cost of this method is higher than traditional, some DOT's allow for a cost-benefit style analysis that makes this more appealing.

Essentially, the particular DOT might say that a given lane-mile of a given highway has a particular $-value per day. These are real costs (due to delays created, etc.) and assigned cost for benefit(s) lost to users.

If the engineer or contractor can then build using this technique showing that it will keep the highway open for X-number of lane-mile-days * $-value and offset the additional cost, then this method will likely be treated favourably.