A new report highlights the fast highway driving along Chicago area highways:

Only a few are obeying the law. In those stretches, an average of 1 out of 20 motorists drives at or below that limit…

The data, gathered in April, May and September, showed that, depending on which tollway stretch was tested, 91 to 98 percent of drivers exceeded the 55 mph speed limit. In those stretches, the average speed ranged from 66 to 70 mph.

The studies followed a 2012 National Highway Traffic Safety Administration report that showed that average highway speeds increased to almost 71 mph in 2009 from 65 mph two years earlier. At the same time, traffic fatalities — 33,561 last year — are dropping, except for a slight increase in 2012. The report concluded that the higher speeds might have been the product of less speed enforcement in 2009 and fewer cars on the road that year, leading to less congestion…

But perhaps the most fundamental metric in deciding where to set a speed limit is a concept known as the 85th percentile, or the speed at which 85 percent of drivers are either traveling at, or below. In essence, it measures the limit that most drivers place on themselves, regardless of posted speed limits.

Tollway data showed that the 85th percentile speed ranges from 71 to 75 mph.

Read on for more discussion of then how Illinois might or might not increase speed limits.

I’ve talked to numerous people over the years who are nervous about driving in the Chicago area because of these speeds. On one trip that involved driving through the Chicago region, I was asked to drive since I was used to it. While the speed is one factor, I wonder how much the overall traffic, particularly the large trucks, matter. It is one thing to drive fast in more open spaces – Michigan, for example, has had 70 mph speed limits for at least several years but it often doesn’t feel as bad with less people around. It is another thing to have at least three lanes and often four in each direction full of drivers of different sizes and speeds.

One thought: if we end up with a world of driverless cars in a few years, what speed would these cars travel on a highway? Presumably, the cars could go faster because the cars would share information and maximize the speed. But what then would be considered “safe”?