Physics of Traffic Jams

I have heard the term "backward traveling wave" can explain why traffic jams sometimes appear seemingly out of nowhere. I have experienced this while traveling down the road. What causes these backups, to appear for no apparent reason?

This past holiday season, many of us took to the roads. Which means many of us faced rather unpleasant traffic jams. The most frustrating ones seem to occur for no reason at all. You're stuck, positive something catastrophic must have happened up ahead. Then for no apparent reason, the traffic clears.

Now mathematicians from England's University of Exeter believe they have solved this mystery. They modeled the effect of various highway events, such as a truck slowly pulling out from the merge lane. If the truck's approach causes the car behind to quickly drop below a certain speed, then the next driver back also hits his or her brakes. This continues in a braking chain that the authors call a backward traveling wave. It could stretch back miles.


So it's not necessarily the volume of traffic, but rather a sudden interruption in the flow that causes delays. The authors advise drivers to pay attention, and, when necessary, brake gently and slowly. If you suddenly overreact and hit the brakes, you could be causing someone to grimace in frustration in a car many miles away.

Ice scrapper windshield damage

I have heard that using an ice scraper can do damage to your windshield, if you don’t keep the scraper blade flat against the glass, and you should never use your scraper on a mirror. Is this so? Most ice scrapers are made of plastic, so why would this hurt the glass? Come to think of it, I have these lines on the glass, that don’t wipe off. Could it be from the scraper?


Actually the sharp corner of an ice scraper almost always quickly breaks up thick ice and gets you on your way. But too often as the windshield defrosts you’ll notice lines on the glass that look like crayon marks. “Must be from the scraper, I’ll wipe them off later.” But the marks don’t wipe off. You try everything from window cleaner to glass polish only to discover the marks are actually scratches in the glass from using the scraper’s edge.

As many drivers have discovered, plastic can damage glass and getting rid of the distracting scratches requires the services of a glass shop. The least expensive fix is buffing the windshield but buffing doesn’t always work making a new windshield your only option. Either way you’ll spend considerable dollars just from using an ice scraper the wrong way. Be doubly cautious about mirrors, they’re also expensive and even easier to damage than windshields.

Most icing problems can be avoided with spray de-icer and windshield covers. Windshield covers are a cloth-like sheet to cover the windshield, which prevents snow and ice from sticking to the glass. Windshield covers wrap around the front pillars and are held in place by the doors. In the morning open the doors and remove the cover along with the snow and ice.

Opening the doors may be a problem unless you spray the rubber door seal with silicone. Silicone is amazingly slippery and lubricates the rubber, which keeps ice from freezing the rubber to the car’s body. But, none of this works unless you can unlock the door so lubricate the door locks with graphite lock lube, before that icy day.

Another problem to watch out for, is clearing ice from the side windows. Dumping hot water over the doors and windows is extremely popular but watch out! On an older car okay, but on modern cars, NO!

Today’s average car door is filled with electronic parts that could be damaged if soaked with hot water on an icy-cold day. Doors now have electronic interior-light switches, one-touch window relays, automatic door lock controllers, and more. Dousing your door full of sophisticated electronics with hot water, might get your going now but it could lead to some expensive repairs later, when you have forgotten about what you did that day the car was iced over!

Blended synthetic motor oil

I have heard that it is better to make your own SYNTHETIC BLEND of MOTOR OIL, rather then buying one that has already been blended. Is this so?

Yes! You can take conventional motor oil and mix it with a full synthetic motor oil. The reason why it is better to make your own is that the blends on the market do not tell you what percentage of the product is synthetic. To qualify as a synthetic blend the oil has to have a very small amount of synthetic in it. Synthetic oils are compatible with conventional motor oils. Making your own allows you to put in as much synthetic as you want!

Filling tires with Nitrogen

I have heard that filling tires with nitrogen rather than air is becoming a common practice in the replacement tire market and that the National Highway Traffic Safety Administration (NHTSA) has seen reduced aging of tires filled with nitrogen. Is Nitrogen worth the price. Has there ever been a study that substantiates some of this?

Yes, Consumer Reports wanted to find out if nitrogen is worth the price, so they purchased a Nitrogen Inflation System and checked out how well the inflation held up over a one year period. They evaluated pairs of 31 tire models of H- and V-speed rated, all-season tires used in our tread wear test from 2006. They filled one tire per model with air and the other with nitrogen. The test was quite simple: fill and set the inflation pressure at room temperature to 30 psi (pounds per square inch); set the tire outdoors for one year; and then recheck the inflation pressure at room temperature after a one year period.

The tires were filled and deflated three times with nitrogen to purge the air out of the tire cavity. They also used an oxygen analyzer to be sure we had 95-percent nitrogen purity in the tire--the claimed purity limit of our nitrogen system, which generates nitrogen gas from ambient air.

The test started on September 20, 2006 and the final measurements were taken on September 20, 2007. The results show nitrogen does reduce pressure loss over time, but the reduction is only a 1.3 psi difference from air-filled tires. The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting. More important, all tires lost air pressure regardless of the inflation medium, so consumers should check their tires' air pressure routinely. No evaluation was done to assess the aging claim.

Bottom line: Overall, consumers can use nitrogen and might enjoy the slight improvement in air retention provided, but it's not a substitute for regular inflation checks.

Article posted from Consumerreports.org