Let's say you want to fix up a length of road. There are various strategies for this. Traditionally, you would perform a "resurfacing": mill away two or three inches of the existing asphalt, and replace it with the same thickness of new asphalt (of a type prescribed by the pavement experts—not all asphalt is the same). However, such a project carries with it certain extra costs, such as the federally-imposed requirement of upgrading all the pedestrian curb ramps in accordance with the ADA standards. In recent years, resurfacing has been largely displaced by "pavement preservation"—the application of a thin layer of asphalt (1 inch or less) directly on top of an existing surface that still is in reasonably good condition. For example (making some numbers up because I'm not a pavement expert), instead of doing a resurfacing every ten years, you might do a resurfacing in year 0, then pavement preservations in years 5, 10, and 15, and restart the cycle with another resurfacing in year 20, resulting in cost savings over years 0–19 in comparison to just doing resurfacings in year 0, year 10, and year 20. (It is being rumored that the asphalt industry now has gotten angry that roadway organizations aren't ordering as much asphalt, and is spinning up its lobbyists to promote a return to resurfacing, so pavement preservation may fall by the wayside in the future.)
So, anyway, let's say you want to "preserve" the pavement on a particular stretch of road—or, rather, the pavement experts in your organization have decided that this particular stretch of road should receive a particular preservation treatment, and they tell your bosses to design the project, and your bosses assign the work to you (the roadway engineer). What's the first step? Getting a survey of the area? No—the first step is getting the jurisdiction maps, to see which roads are actually the responsibility of your organization. You (the reader) already know that public roads in the United States are variously designated as municipal, county, or state roads. ("State", "US", and "Interstate" highways all count as state designation. US and Interstate highways are not owned by the federal government, but a project on a state road can be paid for by the feds if the road is in the National Highway System, or if the state government receives a one-time grant through the Surface Transportation Block Grant program. The state also gives grants to its subordinate county and municipal governments.) What you probably don't already know is that, very often, the jurisdiction does not match the designation. When a state-designated road intersects a county- or municipal-designated road, the state government usually will assume jurisdiction over the entire intersection, including any ramps or jughandles, and sometimes extending several hundred feet up the nominally county-owned road. (This can get very complicated when a state road that's controlled by the Department of Transportation, a state road that's controlled by a different organ of the state government (such as a toll-road authority or an interstate port authority), a county road, and a municipal road all meet in a single interchange.) So you (the roadway engineer) need to check your organization's archive of jurisdiction maps, to see exactly what the extent of the paving will be. Maybe the pavement experts told you to pave county roads X and Y, but it turns out that state road B will chop a few hundred feet out of your project where it intersects road X, and on the other hand municipal road N that runs between roads X and Y was signed over to county jurisdiction back in 1965, and you've also got to deal with some negligible pieces of municipal roads Q and R that intersect road Y. (And, of course, it's possible that the jurisdiction map is missing from the archive. In such a case, you can do nothing but take your best guess.)
What's the next step? The next step is to get a detailed map of the road where the work will be proposed, called "topo" (short for "topographic survey") in the jargon of the field. Ideally, a professional survey was performed for a resurfacing project five years ago, and the electronic files still are in your organization's database (or can be requisitioned from the consultant that designed the project), so you can just make some minor modifications to those files and go on your merry way. More likely, however, no professional electronic survey has been done (maybe the last project that was done on this road was a generic "maintenance and resurfacing" project that used no formal construction plans at all), and your organization isn't going to shell out the cash for a new survey for the sake of a mere pavement-preservation project. Therefore, what do you have to do? That's right. You, the roadway engineer, will have to MANUALLY draw the ENTIRETY of the multiple-mile project yourself—using as a basis either ten-year-old, one-bit-per-pixel scans of fifty- or seventy-year-old "as-built" plans of past resurfacing/reconstruction/original-construction projects, or (if no as-builts are available, which is somewhat unusual but definitely not impossible) dozens of Google Earth screenshots. This can take several weeks just by itself (I can say from extremely painful experience).
But that's not all. Topo alone is not sufficient for laying out construction plans. You also need the baseline—the set of lines and circular arcs that defines precisely where on the 2D plane the highway is located. (Earth's surface is 3D, but each state has at least one "state plane" for survey purposes.) Ideally, a baseline is included with the topo from the five-year-old resurfacing project. If there's no electronic baseline, then the second-best option is that, when the road was originally constructed fifty or seventy years ago, dozens of "monuments" were installed alongside it, and your in-house surveyors can uncover those monuments (find them with a metal detector and literally dig them up from where they've been buried by eroded soil) and get GPS coordinates for them, and you can relate those coordinates back to the as-built's "tie sheets", which are likely to have (1) all the bearings and radii, but (2) either (a) no coordinates or (b) coordinates in an outdated coordinate system that (i) can be manually copied into your CAD software, floating unmoored in the 2D plane, but (ii) cannot easily be converted to the current coordinate system and fixed in their proper place. (Converting between coordinate systems isn't just a matter of translation and rotation. There also is complicated scaling involved. I once tried to convert between coordinate systems using ArcGIS, and ended up with nothing but egg on my face and a shamefully inaccurate set of baselines. But maybe that's a me problem.) More likely, however, you have tie sheets, but the monuments were destroyed and not replaced when the roadway was widened thirty years ago, or no monuments ever were installed in the first place. What is a humble roadway engineer to do in such a circumstance? The closest thing to a monument—something that's very unlikely to have been moved since the roadway was constructed—is a drainage inlet on the side of the road. Therefore, the engineer is forced to use a few dozen inlets as ersatz monuments, send out his in-house surveyors to get GPS coordinates for them all, and manhandle the baseline from the as-built tie sheets (which, again, is just floating unmoored in the 2D plane at this point) to match those coordinates as closely as possible. (If it's a divided highway, don't forget that your organization's policy probably requires you to draw one baseline for each direction. And don't forget to draw baselines for all the ramps as well. This can get pretty annoying, especially when there's a typo in the as-built tie sheet from year 1985 and you need to figure out what's wrong by comparing it with the actual angle of the road.)
What's next? Can we start drawing the proposed work now? No, we can't. Now the engineer must draw the typical sections of the road. The typical sections are just slices of the roadway—not just the surface (lane widths, and the sideways slopes necessary for proper drainage), but also the materials that make up the subsurface (surface course, intermediate course, base course, subbase, the hundred-year-old concrete road that seventy years ago was paved over rather than being "rubblized" into subbase…). Ideally, the limits of your project perfectly match the limits of an old as-built, and you can redraw the typical sections from that raster as-built in vector format with minimal changes. More likely, however, this roadway was drastically reconstructed piecemeal in half a dozen different projects over the years, and the as-builts from those old projects are like puzzle pieces that you must fit together while keeping in mind that some have been partially overwritten by others. (And don't think that you can skip this step just because you're doing a project where the contractor won't interact with the subsurface at all! Even pavement-preservation jobs require typical sections to be included. My current, unusually-large project may end up with as many as seventy different typical sections, which could take up something like 15 or 20 sheets. My bosses are hoping that we'll be able to get their bosses to update the procedures for pavement-preservation jobs so I don't have to spend a week or two drawing all this stuff that the contractor will have no use for.)
Now for temporary traffic control. On a pavement-preservation project, this isn't too bad. Since slathering a thin slurry of bituminous material onto the pavement is a one-night job (the road can be opened to traffic on the following morning), responsibility for determining temporary detour routes falls on the contractor rather than on the designer—and, let me tell you, drawing a detour route for each of the dozen ramps on a project, including a list of all the signs that need to be installed for each detour, is a very tedious task. However, even without detour routes, the designer still needs to go through his organization's list of standard traffic-control details and estimate how many drums, cones, barricades, and square feet of temporary construction signage the contractor will need to employ. (Most contractors will just reuse the equipment that they already have and bid something like one dollar per unit for each of these items, but we are not allowed to make such assumptions in our cost estimates—it's full price for everything.) Even on a pavement-preservation project, you may still need to draw a nonstandard traffic-control detail if the bigwigs who drew the standard details failed to take into account a particular situation, like a ramp or a roundabout. (Oh, you thought something as commonplace as closing a ramp for overnight paving would be in the standard traffic-control details? Well, you thought wrong.)
Finally, we can start figuring out the quantities of the proposed work. Asphalt? No, not yet! I'm talking about the (permanent) pavement markings. You've got to compile a spreadsheet listing every single stripe segment in the entire project—white or yellow; four-inch or eight-inch (or six-inch on Interstate highways); broken (colloquially called dashed), solid, or double solid (or broken on one side and solid on the other side, or that newfangled dotted)—including any upgrades that need to be done (e. g., changing the line along an auxiliary lane from broken to dotted). And don't forget the RPMs (raised pavement markers—those little shiny things that your headlamps highlight when it's raining), with different spacings in different places! And the rumble strips (not just in the outside shoulder, but also in the centerline, or in the inside shoulder if it's wide enough)! And the "markings" (made of a different material than "stripes" proper, thermoplastic rather than epoxy—e. g., 8-inch crosswalk lines, 24-inch stop lines, and "← ONLY" at intersections)! And the separate pay items for removal of the existing pavement markings before the pavement treatment can be applied, and for the application of temporary pavement markings during construction!! (My current project's stripe calculation spreadsheet has around 800 rows, but this project is unusually large. My previous project's spreadsheet had around 200 rows, and my spreadsheet for the project before that had around 300 rows. All three projects are/were pavement preservation.) Oh, and don't forget—three paragraphs ago you drew all the road edges from as-builts. You need to draw all the existing pavement markings as well. (They normally would be picked up in the survey, but this part of the survey technically isn't included in the same "topo" file, since it's shown only on the striping sheets, not on the construction sheets. Or maybe I'm just being too pedantic.) I hope you're proficient with your CAD software's offset tool!
The pavement markings are only the most important part of the "incidental work" that surrounds a pavement-preservation project. Less important, but still needing to be done, is the inspection (typically via Google Street View) of all the drainage inlets that sit in or alongside the pavement within the project limits. If you're a bicyclist, you may be aware that, over the past few decades, the slotted grates that will catch your front tire and flip you over the handlebars have been gradually replaced with "bicycle-safe grates", which replace the long, wide slots with smaller holes. This process still is ongoing. Additionally, sometimes the "curb piece" of an inlet that's embedded in the curb has incurred damage after too many tractor-trailers ran over it, and needs to be replaced. There are the environmental regulations: a curb piece whose mouth is taller than two inches allows too much debris to enter waterways, and must be replaced with one that has a smaller mouth. There are concerns received from the maintenance experts: Way back when the aforementioned environmental regulations were instituted, people didn't want to go to the trouble of replacing all those zillions of curb pieces, so instead they tried affixing a little slotted faceplate to the front of the curb piece in order to cover up the overlarge mouth. It turned out, though, that these faceplates tend to catch on snow plows, so now any curb piece that received that treatment needs to be replaced in its entirety anyway. And, finally, there are the rare occasions where the concrete box underneath the grate appears to be broken (as evidenced by a suspiciously low grate elevation), requiring the entire inlet to be replaced. (And some non-inlet incidental work: the designer should take a field visit on the day after heavy rain, and check for any ponding that can be fixed with some localized milling and paving.)
At long last, we can draw the proposed asphalt. This step is relatively simple, as are the steps of (1) referencing everything into the actual plan sheets, (2) labeling all the proposed work on the construction and striping sheets, and (3) summing up the quantities and plugging them into the (somewhat finicky) estimation software… Wait a minute—did I say it was simple? No! No, you've got to run everything past more environmental regulations! Increasing the elevation of the roadway by just half an inch requires the project to be reviewed for flooding. Some pavement-preservation treatments (thankfully including the one that's being used on my current, oversized project) are thinner than half an inch—but others are not. So now you have to wait for the environmental consultant to review your work. Somehow, the in-house environmental experts who coordinate this review are understaffed even though they've got their thumb in every pie, so your project probably will be delayed by a month or two past its originally-scheduled submission date. And, after all this rigmarole, the environmental experts will tell you to mill down one or two arbitrary 500-foot segments of road by an extra inch, and that'll be that. Also, don't forget to mill underneath any overhead structures, in order to maintain the existing clearance—not just bridges, but also sign structures. I hope you didn't forget to draw the sign structures into your topo file! They probably aren't included in the roadway as-builts that you were looking at before, because structural stuff is done separately, so it's back to Google Earth screenshots for you. And also-also you've got to do a little bit of milling wherever your new pavement meets old pavement (at intersections and at ramp terminals), in order to avoid a sudden change in elevation (also known as a bump). And also-also-also you need to mill along the curb, because otherwise you'll change the drainage characteristics of the roadway. And finally don't forget to ask the electronics experts about any electronic stuff that's embedded in the road—you can't mill over it without replacing the whole system afterward. (But maybe the electronics experts want it to be replaced as part of the same project, since you're already working in the area.)
After that, it passes out of your hands and into the hands of the bigwigs who do pencil-pushing stuff like drawing up the tentative construction schedule, compiling the construction specifications (the standard boilerplate, a bunch of lines that need to be filled in by the designer, special stuff that the pavement or environmental or structural experts think need to be added, affirmative-action requirements from the "affirmative-action experts", construction-office requirements from the construction experts, etc.), and making the final electronic submission to the bigger wigs (the project manager, the in-house reviewers, and I think some kind of FHWA review).
For the xianxia fans: 哭笑不得 (I don't know whether I should laugh or cry). For the zoomers: 😂.
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ADA Sidewalk requirements are a huge huge deal and impact road repair and construction more than people realize. Basically most existing sidewalks are not built to current ADA standards, and the feds requirements for this is that it's fine to leave what exists, but if you have a project that those sidewalks are within, you have to bring them to ADA. Typically this will mean curb ramp, but occasionally you'll have to replace entire runs. The issue then is that if you have a city road that's beat to shit, you can mill it off, go down a few inches (or a few feet if you need to do utility work) and repave and it's reasonably fast and cheap and will, as mentioned by OP, last you around 20 years. On the other hand, if you need to replace every curb ramp at every intersection along that run, your costs and time impact will balloon. Depending on how the current curb ramps are built, you may need to redo big chunks of sidewalk behind them to get things flat and wide enough. Worst case you might be talking about relocating utility poles. This leads to situations where road that needs a repair won't get the 2 million dollar job that would get things working good again, and instead your agency will wait till it's truly falling apart and they can take the whole thing apart and redo utilities and signals and etc. for 20 million. That's fine and dandy once it happens, but it means you have a beat to shit road for an extra 10-15 years.
There's a similar issue with overhead utilities, as many municipalities have laws that require you to bury lines if you do a job in the area & underground conduit runs are one of the more expensive things you can do. Alright peace.
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