Low clearance, low clearance with warning
Low clearance, low clearance with warning
Low clearances are the bane of most eastern cities and towns in the US, though the west is not free of them either. Originally designed for streets carrying vehicles that did not exceed 10 feet in height, today's modern trailers, accommodating a double stack of palettes, is standardized at 13' 6" in height. Rebuilding overpasses to accommodate that height is not always a simple or cost-worthy possibility. Most of the low clearances involve roads that pass underneath railroad tracks. Such tracks are enormously more expensive to change in elevation, and digging the underpass deeper involves expensive abutment foundation work, so many still exist. The second most likely cause is older bridges with truss superstrucures. These are being replaced with non-trussed bridges as they age and are replaced in due course.
Low clearances is a new feature of TruckTrek, and is just starting out. Currently there are more than 760 intersections in the database, but it is estimated that there are more than a thousand low clearances in the United States. This means that only 70% of the low clearances are currently in our data, but among those 90% have been checked out and located precisely. TKE will be working to improve the completeness of this database, vital to both truckers and RVers.
The most important feature about clearances is, of course, the clearance height, especially for RVers whose heights are less standardized than cargo trailers. Most states consider 13' 6" (162 inches, or 4.16 meters) to be the height above which they don't need to post a warning at the structure. Thus the immediate information includes the height and a description of the structure (as in, "Cheltham Rd crosses under RRT", where RRT means railroad tracks). The height is usually just a guess, though, and may be as much as 6 inches off, as roads get repaved, settlement occurs and so forth. Even those where the state has posted a clearance height can be well off, and in many places the height is simply not posted at all. Also be aware, as some truckers have forgotten to their sorrow, that an unloaded trailer will ride several inches higher than the loaded trailer that got under free earlier in the day.
There are an unusual number of low clearances flagged with warnings in the form of the green icon above. Happily, these are mostly truss bridges with low clearance superstructures which have been replaced with modern bridges with no superstructures. TKE keeps them in the database to avoid confusion when a driver knows from the past that there is a low clearance bridge "somewhere around here", unaware that it has been replaced.
A low clearance covered bridge in Delaware. Bridge imaged above.
Most low clearances are only declared on numbered state or local roads, with a few exceptions. PNAME attempts to locate all structures that may occur on any feasible truck route. However, at the mention of low clearances, most truckers' thoughts turn, inevitably, to Chicago. The wide use of railroad transport coupled with suburban sprawl has created a large number of low clearance locations. It is known in many areas that locations separated by a few hundred feet may require miles of driving to get to safely. Because Chicago is such an exquisite problem TKE has added a separate series of icons for all of the low bridges that we have been able to locate. These are separate so they can be deleted for those who don't need them; many are on residential streets. TKE is considering more in his series in other ciies which may need tham as time goes on.
Let us emphasize here that TKE attempts to verify as much of its data as possible, and prides itself on the accuracy of that data. This does not mean that it is ever 100% correct, however, and the user agrees (see our license) that the data is supplied only for informational purposes. The driver is always responsible for decisions on the spot. If errors in this data are detected by the user, then TKE very much desires to hear about it, in this database most particularly.
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