Bugs on the windshield at high speeds

I agree with Tom and Ray’s assessment of the Bugs on the windshield of the Mercedes in the 5-8-2010 episode of CarTalk, but listening to the show, I was not sure of their reasoning.

The reason you get more bugs stuck on your windshield at high speeds is that, although as the caller pointed out the airflow over your car is faster and smoother, the heavier airborne bugs cannot change direction as fast as the air, so although the air deflects smoothly up and over the car, the bugs travel straight into your windshield.

As an aircraft mechanic, I have seen this principle used on the intakes of some turboprop aircraft, such as the DeHavilland Twin Otter. A duct can be lowered into the intake (by the pilot) which requires the air to make a tight 90 degree turn just as it enters the engine. The air can make this turn just fine, but any airborne particles cannot and end up flying straight out the back of the engine, bypassing the delicate internals.

As an aside, the “bug deflectors” that you can mount on the front of your hood work well. I put one on my '95 Ford Taurus and it kept the bottom 3/4s of my windshield bug-free, as well as helping me see better in the rain. I know it probably some negative effect on gas mileage, but I wasn’t able to see a noticeable difference on my car.

A particle separator for the front of your car - Brilliant! Good analogy.

Interesting phenomenon. I live in Central Florida, where every May and September, we are bombarded with love bugs. I’ve noticed that cars coming off the FL Turnpike are usually completely covered with bugs (I’ve had the same problem as the caller, where I had to wash my windshield before I headed home, because the trip there had gotten me so bug-plastered). However, at the same time of year, cars driving on nearby highway 417 usually only end up with a few love bugs on them. It sounds like the bug weight to car speed ratio is “just right” at the 70+ mph speed limit on the turnpike, whereas the 417’s 60 mph (give or take) speed limit is low enough the love bug’s weight allows it to surf the wind.

I’d always assumed it was something different about the Turnpike’s heavier traffic, like perhaps it made the road hotter, thus attracting more bugs. This explanation, especially as clarified by the commenter above, makes more sense. Thanks!