By Tim Baxter, Road Safety and Loss Prevention Specialist
Low Water Crossings can be a huge benefit in reducing expense when replacing drainage structures on minimum maintenance and local roads, but they can also be a huge liability to the county if they are not designed and signed properly.
Low Water Crossings are usually installed on minimum maintenance roads but are only allowed on local roads with 50 ADT or less. The road cannot be the only access to an occupied dwelling. A relaxation of standards is also required from the Board of Public Roads Classifications and Standards prior to construction of the low water crossing. See section 5B.01 on page 21 of the 2019 Nebraska State Supplement to the MUTCD.
I have traveled many times on low water crossings installed in channels that are way too deep without the proper approach cuts to safely travel across the structure. I’ve seen improperly designed low water crossings, crossings without the proper signage, crossings plugged with debris preventing storm water from moving under the crossing, etc. Any of the aforementioned problems could cause an accident, which can in turn result in a claim and/or lawsuit against the County.
Always have a competent, qualified, and professionally licensed civil engineer design your low water crossings. Yes, it may cost more than throwing a 24-inch culvert in the channel to replace a 30 ft. drainage structure. But the extra expense will help prevent accidents and put your County in a more defensible position should an accident occur. Check your engineer’s background to ensure they have experience in the design of low water crossings, physically view some of their completed projects across the state to ensure they are qualified to design your low water crossing projects. Improper designs, including approaches that are too steep, can result in roadway wash outs during storm events, which at a minimum is likely to cause constituents to complain, even if you are lucky enough for no accident to occur.
Low Water Crossings must be signed properly as shown on pages 18 through 21 in the most recently adopted edition of the Nebraska State Supplement to the MUTCD or the 2019 edition. Approaches to low water crossings must include “LOW WATER CROSSING AHEAD” and “DO NOT ENTER WHEN FLOODED” signs installed the proper distances in advance of the crossing. Without these signs motorists are unaware of the drop in elevation or the possibility that water could overtop the road. NIRMA would have a very difficult time defending your County if you have not properly warned motorists of the upcoming hazard.
Counties often forget or do not think object markers are required on the corners of low water crossings. At minimum, type 2 object markers should be installed on all four corners of the low water crossing drainage structure, or at the rocked or armored bottom of the channel, as appropriate for the situation.
Another type of signing I rarely see approaching low water crossings are advisory speed plaques. One of the goals of a low water crossing is to transfer the flow of storm water across the road at a specific location and not flood or wash out the entire road. In order to accomplish that goal, most, if not all, low water crossings have a road elevation drop to the structure itself, sometimes a significant drop in elevation from the roadway approach. I don’t believe I have ever NOT had to slow down to safely navigate a low water crossing. Nebraska state statutory speed on county aggregate and dirt roads is 50 mph, which is way too fast to safely travel the majority of low water crossings in the state. Always perform a speed study on the low water crossing and install the proper advisory speed plaques below the “Low Water Crossing Ahead” signs to warn motorists to slow down. The aforementioned information will greatly assist in the defense of your county should an accident occur on one of your low water crossings and a claim and lawsuit be filed.