2016-07-14 – Chicago gets a bad rap for many things. We are (supposedly) the murder capital of America, even though our murder rate is about one-third that of cities like St. Louis and Detroit and less than half that of New Orleans, Baltimore, and Newark. Our schools are in crisis. Our city and state governments are dysfunctional. We could have been hosting the 2016 Olympic Games, but Rio beat us out!

There is one thing we have going for us: Chicago is a bike-friendly city.

This is not based on any statistics. I am not going to look it up. I am basing this on my own experience. There are great bike routes in all directions from my house, other than east which gets you submerged under Lake Michigan before you ride very far. But riding along the lake is great—south into the city, north (via the Green Bay Trail) as far as the Wisconsin border, west to Caldwell Woods. In the last few years we’ve seen a proliferation of designated routes both in the city and in neighboring suburbs.

But an odd thing seems to be happening. (And this is based on my own observation.) With more and more marked bike routes available, it seems like more and more people are riding on the left side of the street.

Don’t do this.

If you don’t think too hard about this, you might believe that riding on the left side of the street is a good idea. After all, when you ride on the left side, you can see traffic approaching.

Unfortunately, your safety doesn’t depend on you seeing the car about to hit you. Your safety depends on cars being able to see you!

Here’s the math.

If you ride against traffic at 10 MPH and the traffic is going 30 MPH, your speed relative to the car is 40 MPH. If you ride with traffic (and the same numbers apply), your speed relative to the car is 20 MPH.

The basic equation is:

Where,

d = distance, r = rate (or speed), and t = time.

We are considering two different relative rates here, the differential rate when you bike with traffic (r_with = 20) and the differential rate when you bike against traffic (r_against = 40). If we plug these values into the equations, we will get two times: (t_with = time a driver has to react when you bike with traffic) and (t_against = time a driver has to react when you bike against traffic). So let’s solve the equation for any distance d.

We see these both equal d, so:

Solving for t_against, we find that:

t_against = ½ t_with

This means that a car approaching you head on has half the time to see you as it would have if the car approaches you from behind. Those extra seconds can save your life.

These same numbers also mean that a car hitting you from behind will have half the impact of a car hitting you head on. So ride with traffic!

And don’t be looking at your smart phone while you are biking.