When hard-packed snow makes roads icy and dangerous, even trail shoes will not give you good traction. If you want to run safely under those conditions, you can buy a pair of spiked winter shoes like the New Balance 921, which cost about $150. They work well, and I would never discourage you from buying a pair if that price doesn't bother you. At about $20 a pair, you could opt for slip on traction contraptions like YakTrax. I've tried these, and they provide excellent traction, but they are a bit bulky and add a lot of weight to your running shoes. Also, they are prone to wear out under the mileage distance runners put on them. The last pair I bought didn't make it through February.
There is another alternative that adds little weight and no bulk to your shoes, and costs only about a dollar.
If you're a typically obsessive/compulsive runner like me (don't deny it), you have a few dozen pairs of shoes that are not in your current rotation, but which you cannot bring yourself discard or recycle. So, select the best pair from among these, chase out any critters that may be nesting in them, knock the clumps of dirt and stones from them, and take them down to the workbench.
Get out the variable speed drill. Don't even try to tell me you don't have one of these. (If you don't, you can use a screw-driver, but you will have taken all of the fun out of this little project and you will feel very lame.) Go to the cabinet and get a couple dozen hex washer head #6 or #8 x 3/8 inch zinc plated sheet metal screws (not the ones with the self-tapping points.) If you don't have these either, stop by the local hardware, say 'Hi' to Frank in the fasteners aisle, and ask for his help. You may want to buy a few extra. That way, when you drop one or two on the floor and they roll under the workbench, you don't have to crawl on the floor and move out all the paint cans and scraps of wood to find them.
You are going to drive about a dozen screws into each shoe, but let's start with just one. Don't worry about the pattern just yet, but be careful to drive each screw into the tread, not the space between the tread. They will be more effective in giving you traction that way. Another reason is so the points don't come through the bottom of the shoe and into your foot. If you do this, the blood will stain your socks, and also wolves will be able to follow the trail of blood.
When driving the screws into the shoe, use the lowest speed and watch carefully. Stop as soon as the screw head shoulders up to the bottom of the shoe. If you continue to drive the screw beyond this point, the screw will spin and remove material from the shoe, drilling a nice little hole from which the screw will fall after you take three steps. Then you will have just a hole. This hole won't help your traction, now will it? No...no it won't.
Usually, I drive four screws into the heal. If you are a mid-foot striker (shame on you if you're not), you'll find these come into play mostly on the downhills. You can scatter the rest of the screws randomly, or in whatever pattern you find aesthetically pleasing.
There. That's it. How long did that take...maybe ten minutes? Keep in mind that these shoes are to be reserved for running on snow-covered or icy roads, otherwise you will quickly wear down the screw heads, and you will sound tap-dancing troupe out for a run.