# Why did Caltrans spray oil on the shoulder? **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2004, 8:31pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296 "2004-08-30T20:31:09Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [August 30, 2004, 8:31pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/1 "2004-08-30T20:31:09Z")
Hey All, Friday I saw the darndest thing. Location: Northern California Highway 101 North of Santa Rosa. Action: Caltrans truck spraying oil on the shoulder. Comments: It looked like a converted water spraying construction truck that is used to keep dust down during grading, but it was spraying oil. I know it was spraying oil as another truck was driving slow a hundred yards behind it, effectively closing the slow lane (right most lane), with a big sign saying somthing close to, “Oil Spraying Ahead”. I also noticed that there were pieces of plywood over the drains with sandbags on them. Why would they do that? Could it be in preperation for adding an additional lane, or weed control??? \<—speculating wildly Thanks, -Sandwriter ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 30, 2004, 8:53pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/2 "2004-08-30T20:53:08Z")
Could be weed control, but I’ll bet it’s “sealant slurry”, something used to extend the life of asphalt. ---
**Author:** ![DeVena](https://avatars.discourse-cdn.com/v4/letter/d/dec6dc/32.png) [@DeVena](https://boards.straightdope.com/u/DeVena)\ **Post date:** [August 30, 2004, 8:56pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/3 "2004-08-30T20:56:11Z")
I would think it’s for weed suppression or vector (insect or mosquito) control. Here in Alabama, the Highway Department mixes pesticides or herbicides into diesel fuel or kerosene to spray on the right-of-way. The sandbags and plywood are to limit the amount of pollution reaching nearby streams. Note: California environmental regulations are much more stringent than Alabama. You might want to contact [Caltrans](http://www.dot.ca.gov) - (916) 654-5266. ---
**Author:** ![bughunter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bughunter](https://boards.straightdope.com/u/bughunter)\ **Post date:** [August 30, 2004, 11:02pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/4 "2004-08-30T23:02:50Z")
It used to be common practice to spray oil on dirt roads in rural areas to keep the dust down. The oil would bond with the dirt/gravel and become lightly polymerized by sunlight, and act as a cheap sealant. I grew up in South Carolina where this was common thru the early 70’s. Until they realized that the PCB-laden transformer oil was a really _really_ bad thing to be spraying willy nilly about the place. If CalTrans was spraying oil on the shoulder, it was probably dust control… possibly in preparation for imminent roadwork. The covered storm drains are a good clue. Water only works until it evaporates. Oil doesn’t evaporate completely. And oil is not a very effective way to control weeds. Water is a much better way to distribute herbicides. ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [August 30, 2004, 11:34pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/5 "2004-08-30T23:34:32Z")
Another thought: They wouldn’t be chip sealing the shoulder, would they? Chip seal is when they lay down a light coat of oil, a lift of pea gravel (or smaller) on top of that, and let the oil “glue” the wearing surface (the gravel) to the course underneath. Then either they compact it or let the traffic driving over it compact it, then sweep up the excess gravel. I wouldn’t use it for an actual traffic course on bare compacted dirt at all. Not strong enough for continuous use, but _maybe_ a shoulder? I dunno, thoughts? I’m just throwing out a possibility. **SandWriter** , were they spraying the “oil” on bare dirt, or an asphalt shoulder? Tripler Like I said, it’s a possibility. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 31, 2004, 12:39am UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/6 "2004-08-31T00:39:26Z")
“Seal slurry” and “chip seal” are either closely related, or the same think. ---
**Author:** ![SandWriter](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@SandWriter](https://boards.straightdope.com/u/SandWriter)\ **Post date:** [August 31, 2004, 9:31pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/7 "2004-08-31T21:31:14Z")
> [@Tripler](#): > > **SandWriter** , were they spraying the “oil” on bare dirt, or an asphalt shoulder? They were spraying it on an asphalt shoulder. Also, they have not followed up with gravel or some other coating. I have e-mailed Caltrans from DeVena’s link, and I’m **not** holding my breath for a response. ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [August 31, 2004, 10:39pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/8 "2004-08-31T22:39:56Z")
[QUOTE=bughunter] It used to be common practice to spray oil on dirt roads in rural areas to keep the dust down. The oil would bond with the dirt/gravel and become lightly polymerized by sunlight, and act as a cheap sealant. I grew up in South Carolina where this was common thru the early 70’s. Until they realized that the PCB-laden transformer oil was a really _really_ bad thing to be spraying willy nilly about the place. [QUOTE] I don’t know how to break this to you, but… I live in Orange County, New York. They oiled my road a MONTH ago. They use the identical method described- they follow the oil truck with gravel spray. After a week or two, the dust and filth settles down and it is the poorboy approximation of resurfacing. Disgusting. ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [August 31, 2004, 11:54pm UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/9 "2004-08-31T23:54:22Z")
> [@SandWriter](#): > > They were spraying it on an asphalt shoulder. > > Also, they have not followed up with gravel or some other coating. Hrm, if they had _sprayed_ it onto a “bare dirt” surface, I would have agreed with the majority that it’s just a dust cover. But, can you let us know if they follow it up with a lift of pea gravel? But, I’ll put the next DopeFest pitcher of choice they’ll be chip sealing the shoulder. Any takers? 😃 Tripler Now if they’d have _drizzled_ it into the cracks, then I’d agree with **DrDeth**. ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [September 1, 2004, 12:43am UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/10 "2004-09-01T00:43:06Z")
You _drizzled_ oil in my pea gravel !!! Hey, you _sprayed_ pea gravel in my oil !! Two great environmental offenses that taste great together !!! :rolleyes: ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [September 1, 2004, 1:07am UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/11 "2004-09-01T01:07:20Z")
> [@Cartooniverse](#): > > You _drizzled_ oil in my pea gravel !!! > > Hey, you _sprayed_ pea gravel in my oil !! > > Two great environmental offenses that taste great together !!! > > :rolleyes: I understand about not wanting more petrochemicals in the environment than are needed, but how is pea gravel damaging to anything but your body work? ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [September 1, 2004, 1:16am UTC](https://boards.straightdope.com/t/why-did-caltrans-spray-oil-on-the-shoulder/262296/12 "2004-09-01T01:16:10Z")
There are no sidewalks on my street- nor any shoulder at all. People walk in the roadway, drivers watch out. How is the pea gravel dangerous? 1. Trashes your undercarriage. 2. Is sprayed backwards violently when cars accelerate from the stop light. Thousands of small projectiles. 3. Causes skidding/ collisions because it takes at least a week for the tires to slowly impress the pea gravel INTO the layer of sprayed oil, making for a new “surface”. 4. The fine stone dust that is part and parcel of dumped pea gravel makes for miserable breathing. ( I’m athsmatic ). So yeah, for the first week at least, it’s environmentally and physically unsafe.