Though this blog is dedicated to updates on active construction projects, periodically we are asked some pretty good questions that deserve more of a response than 140 characters will afford.
Over the weekend's weather event, we were asked why we don't use salt to eliminate and protect against ice, as transportation departments in northern states use. Some of those asking suggest we might be able to avoid closing the highway or highway interchanges if we were to use salt. Those asking hail from northern states and have seen ice and snow events much worse than what we encountered over the weekend, and the claim is that those events up north don't shut down the highways like our events do.
The truth is, even northern states are starting to switch over to saltwater brine. According to one report, salt chat only works on ice that's already been formed and only when temperatures remain above 15 degrees Fahrenheit. The New York State Department of Transportation has opted to switch to brine solutions as a proactive measure, citing brine as more effective than salt chat.
Brine is an anti-icing saltwater solution with a salt concentration of about 23 percent. At that concentration, the freezing temperature of water sinks to about zero degrees Fahrenheit. Brine is applied at rates adjusted for anticipated weather conditions ranting between 30 and 60 gallons per lane mile.
The brine helps create a barrier between the ice and the roadway, stopping ice from bonding to the road or, in the case of south Texas, from forming in the the first place. This proactive approach is among the most cost-effective (and environmentally safe) practices in winter road maintenance.
Just how cost-effective is saltwater brine? Even in 1995, the Iowa DOT produced a document describing the cost savings of using saltwater brine in tandem with salt chat, observing that saltwater brine isn't effective when snow and ice build up over a period of time - not an issue in south Texas.
Perhaps most interestingly, the Iowa report shows a cost breakdown of roughly 5 cents per gallon of brine and about $30 per ton of salt chat. Using just one or just the other, that means the same lane mile would run roughly $3 either way; no real financial gain. For Iowa, though, the use of saltwater brine reduced the need for salt chat by some 25 percent (the brine prevents salt chunks from bouncing off the roadway, being wasted). The result is a cost-per-mile of roughly $2.25 using a combination of brine and salt.
But those numbers are old - 1995 was a long time ago (20 years!), and salt chat prices are dramatically on the rise. A Michigan report from November tells of the cost of salt rising by more than 40 percent this year, landing at $65.81 per ton (average). Other states are reporting costs in excess of $100 per ton. That means your average lane-mile of roadway would run between $6.60 and $12 to treat with salt alone. The brine solution for the same stretch? About $4 (about 6 cents per gallon). None of that includes the delivery fees, of course, driving the price on all items upward.
There are additional costs to consider as well. For starters, salt chat would need to be stored somewhere, and those storage places would need to be climate controlled to a degree (salt dissolves in warm water that would come in south Texas rain storms). What's more, these storage areas would need to be built in the area, where they're not currently existing. Once built, there are maintenance costs to consider.
The box spreaders we would need for salt chat are indeed in our inventory, but to make the most out of our salt we would likely need something other than what we now have. There are more efficient spreaders in the industry that claim to reduce wasted salt (again, bouncing off the roadway or scattering away from the travel lanes), but those machines come at a hefty price added price - one we couldn't afford for equipment that may well sit, unused, some 48 weeks of the year.
For brine, we actually use the same spray trucks crews use during the summer to spread herbicide and don't require additional attachments for more efficient spreading. TxDOT is considering the purchase of special equipment that would allow the brine to be made on-site, but that equipment is much less expensive than the spreader boxes needed for the salt chat. The brine-making tanks would reduce the price of brine by more than 95 percent. Making the brine on-site would also completely eliminate the need for long-term storage.
Meanwhile, TxDOT continues to use other means of protecting prepared drivers from the perils of winter driving. We do use rock chat on select areas prone to black ice (particularly overpasses or bridges in the hill country) where low traffic volumes mean less friction on the roadway surface and lower road surface temperatures. We use magnesium chloride where deemed appropriate. In northern portions of the state, where snow or ice buildup is indeed possible, we do use salt and sand mixes.
But in the San Antonio area, we're looking for the most cost-effective way to treat a roadway for a light icing. Saltwater brine seems to fit that bill and is emerging as a frontrunner in solutions for this issue. Will it guarantee our roads remain open all year long? No - we did close a number of roadway segments Saturday morning. But those closures were as precautionary as they were temporary, and we had every road lane available for use within about six hours.
Not too bad for a group that can count on one hand the number of ice events we see during a year.