Maximum grade to prevent drag boat trailers 1

[aas1]

I am raising the grade of a rural collector road to improve sight distance at a T intersection with a local road. I am raising the grade approximately 3.5' and would like to minimize the construction on the local road which dead ends and services an island where every property owner has a boat. What I need to know is what is the maximum grade that can be used on the local road to prevent a boat trailer from dragging when manuvering through the intersection. Any help is appreciated.

 

[ACtrafficengr]

I'm sure boat trailers vary widely, in terms of tongue length, rear overhang, etc. Maybe one of the automotive fora might be able to help?

 

[KRSServices]

Due to the variety of trailers (weights and lengths) vs pulling vehicle, I would provide a geometry that does not exceed 3% ideally and maximum of 5% grades. Even 5% may be a little dicey, depending on the intersection geometry.

KRS Services

http://www.krs-services.com

 

[treg]

Is the actual grade the problem in dragging a trailer, or the change in grade?

 

[sc]

The change in grade should not be a problem provided there is a suitable length of vertical curve. I would suggest that one way to check the risk of dragging is to talk to a boat dealer and see what sort of maximum length boat trailers can get to. With this information create a template that shows the rear wheels of the car, the trailer geometry (wheels, length heights to various points on the trailer and tow hitch when connected to a car) only select a worst case car/trailer combination (lowest tow point, longest trailer). Draw the template at a suitable scale, draw the intersection grade changes (along the travel surface) and then simply "drive" the car/trailer over the surface.

I know it is a "basic" method but it does work reasonably well for one of issues. I have used this method for similar problems, more often than not it is actually used to assess and modify driveways.



regards
sc

 

[aas1]

Thanks to all of the responses. What I am proposing is about 250' of construction with reverse 100' vertical curves and a 4.25% grade between the PI's. I like the idea about making a template and "driving" it through the intersection. I have since found that my office has addressed a similar problem with horse trailers the same way. I will approach it from that angle. If anyone else has other suggestions, please let me know. Thanks again.

 

[marks55]

I recently researched this issue for "lowboy" trailer problems associated with a raised crosswalk. I found an article written by a masters candidate at the UWVa who did extensive research on the gometry of potential "hangup" situations for different vehicles - one (group) of which was passenger vehicles and trailers - you can find the PDF document at:

etd.wvu.edu/ETDS/E2391/Clawson_Amy_Thesis_etd.pdf