Left or Right?

Picture yourself in your ambulance, at a post, waiting on your next call.  After a few minutes (probably right after you recline your seat and pull your hat down over your eyes – dispatchers do use hidden crew comfort sensors, after all), you are assigned to an emergency call a couple miles northwest of your current location.  You are in a city that has a grid layout, without many diagonal streets.

For this scenario, let’s assume that each street you choose is a main route without noticeable difference in speeds or traffic volume. You are faced with the “two sides of a square” issue.  You could go north then west, or you could go west first and then north.  Which route do you take?

UPS delivery drivers would take the west-then-north route, because it involves a right turn.  UPS has optimized their routing since the early 2000s to minimize left turns.  I thought it was an urban legend, but there are several articles available on the subject.  It was even tested on Discovery Channel’s Mythbusters show. 

Turning right at an intersection is better for UPS in a few ways.  First, time is saved because the driver doesn’t have to wait for oncoming traffic to clear before making the left turn.  Sitting and idling while waiting for the green left-turn arrow is bad for fuel and time.  Second, right turns can usually be made through red lights.  Idling at the light is reduced, saving fuel and time.  UPS reports that approximately 90% of their turns are right turns.  It got me to thinking about whether that would hold true for ambulance routing during emergency (lights and siren) travel.  Should I be trying to route for right turns, as well?

After thinking about it, I don’t think it does.  I think emergency ambulances should prefer to make left turns.  I don't have academic studies from peer-reviewed journals to cite, but let me see if I can convince you with logic.

The two main reasons to prefer right turns don’t hold true when you are bright, flashy, and making a lot of noise.  Oncoming traffic will stop for your left turn.  Right turns are more dangerous during emergency response.  Let me show you a poorly drawn example:

You pull up to this intersection, intending to make a right turn, where the 1-3 lanes are blocked.*  Which lane would you use? 

The turn lane, correct?  I would.  It would probably take too long to push the four cars through the #3 lane, against the light, to make the right turn.  The problem is that using the turn lane signals to other drivers that the vehicle in that lane is turning left.  It is subconscious.  Vehicles in the turn lane turn.  Other drivers probably don’t even have much of a conscious thought about it, outside of being glad that the ambulance isn’t behind them. 

Turning right from the left lanes is a problematic situation:

Arrows that cross are bad.

If the light changes to green (and if you are in a city with signal preemption devices it will) the cars in the three through lanes are able to go forward – which they will do if they are distracted, not attentive, or in a hurry.  In an ambulance, that is hard to see what’s going on in those lanes because your lateral view is blocked by the ambulance box.  Your partner could roll down his/her window and hang out of it to see those lanes, but that doesn't look especially cool or work very well.

Left turns are better:

No crossing arrows. Visibility is better to look at oncoming traffic, rather than traffic behind you to your right.

I’ve been involved in at least one grinder by turning right in an emergency vehicle with other cars on my right.  I’ve seen or heard of several other ambulance crashes that result from this situation.  Left turns are safer in an ambulance and the efficiency issues that UPS is trying to overcome don’t apply to emergency travel.  So going back to the initial scenario, I think the north-then-west route is best for the ambulance to take.

What do you think?  Did I convince you of the logic behind emergency lefts?

*Lanes are numbered from left to right, not counting turn lanes – like reading.  The left lane is #1, the center lane is #2, and the right lane is #3.