We get so busy with life, we forget
how dangerous a simple left turn can be...
[TV:] "...killed after being hit by a Utah County Sheriff's Deputy..."
[TV:] "That deputy was on his way to a SWAT situation."
[TV:] "The fatal crash is being investigated..."
When a crash happens, we want to blame somebody.
It helps us make sense of the pain.
Yes, they both made some minor mistakes. The kind of mistakes you and I make every single day.
Yet they suffered severe consequences.
And that happens in crashes all over this country every single day.
And it's easy to get in and blame the city,
though 99% of the time, cities follow the rules. They use engineering best practices.
So, we're back to the blame game-- pointing fingers at each other.
Which doesn't solve the underlying problems that cause crashes in the first place. So
we have to look more philosophically at what the road is doing for us--
and what it's not doing for us. Where are the strengths?
Where the opportunities for something better?
I can think of one thing we should be looking at; something you might not want to give up.
it has a rather unfortunate nickname-- that special lane in the middle of a
busy street, which lets you make left turns wherever you want-- from either direction.
[Lewis:] "Turn lanes have that nickname."
(And YouTube will demonetize the video if I say it...) but you know it.
[Lewis:] "Fair or not, they can be maybe not as safe as we would like."
Jeff Lewis is a safety engineer. His goal is to eliminate all fatalities on Utah roads.
And sometimes, these handy but troublesome little lanes make his job difficult.
[Lewis:] "Especially on a busier corridor, depending on how many lanes you're dealing with.
"You've got vehicles turning in and out of driveways, crossing lanes of traffic."
They have a proper engineering name: two-way left turn lane.
Nicknamed: "twiddle."
[Lewis:] "Yeah, turn lanes. I mean, we have them all over. They're the primary
median type on our urban corridors."
In the early days of the motor car there were just... lanes.
Streets generally didn't separate out if you were trying to make a turn. So,
if you wanted to make a left, you had to block traffic. Which meant
coming to a stop in front of traffic-- cruising straight, at the speed limit.
Unsafe and bad for efficiency.
[Lewis:] "The left turn lane provides a space for a turning vehicle to get out of a through lane."
As traffic approaches your rear bumper, you're no longer having to
watch the rear view mirror hoping, "Oh, please stop... please stop."
[Lewis:] "It reduces that potential for rear-end crashes."
It also separates the two directions of through traffic. That can reduce head-on crashes.
A nice cushion.
A baby version of the buffer on high-speed country highways.
To get a turn lane on a bigger street, it may mean widening the road.
But on smaller streets, you might just ask yourself: do you
really need two lanes in each direction? I mean, if there's really that many cars,
you probably need the turn lane-- But if traffic is light enough that
you don't need the turn lane, then you probably don't need two through lanes.
So, you can turn it into something useful:
like turn lane. And maybe a bicycle lane. Or on-street parking, while you're at it.
On streets with medium amounts of traffic, turn lanes are wonderful. They create a
launching and landing point for people turning onto the street or turning off of the road--
any place you want.
But like a pre-pandemic Las Vegas buffet, a big crowd can turn a feature into a failure.
[Lewis:] "When you have that open two-way left-turn lane, allowing people to turn
wherever they please, there's so many conflict points involved."
That term is one of the most important in traffic safety.
Conflict is any place where two vehicles can collide in three basic ways:
1. Places where we intersect and can t-bone each other
2. Places where we merge together and can sideswipe each other
3. Places where we split apart and could get rear-ended as we're slowing down.
[Lewis:] "The typical intersection has 32 conflict points."
[Flex Seal parody:] "That's a lot of conflict!"
More than you might expect.
But each is a statistical probability that a crash could happen. And as the number of cars increases,
so do the number of crashes.
That's when turn lanes start to be a problem.
[Lewis:] "There's a lot of stuff going on at a big signalized intersection,
"with the left-turn movements and right-turn movements.
"And when you add into that someone wanting to make a quick turn into a Taco Bell on the corner,
"you know, that just adds to the chaos."
Because it's not just the intersection which creates conflict points.
It's anything which acts like an intersection... like driveways.
Yes, every single driveway along the street adds more conflict points.
And on a street with a lot of traffic and a lot of driveways, it's a recipe for disaster.
No engineer would intentionally design this.
[The Engineer:] "Nope!"
Yet, corridors like these are all over the country.
Chances are the street where you go shopping is a mess of conflict points.
These can work okay when conditions are right, but quite often they're not.
So how did we end up with the roads that are not okay?
[Lewis:] "It may have started out as an old farm road, that turns into a paved road,
and then, you know, two lanes grow to four or five lane road."
A road has two jobs. One is to get us from point A to point B.
As fast as we can. And with as few interruptions as we can.
It's called mobility.
The second job has to do with points A and B themselves.
For our journey to start, point A has to connect to the road. And for our journey to end,
point B has to connect to the road.
And if WE get driveways-- YOU get driveways.
You get a driveway... and you get a driveway...
and you get a driveway... and everybody gets a driveway!
Businesses start locating in the middle to capture our back and forth traffic
and that's how you end up with a long strip of driveways.
[Kramer-esque character:] "Hey, stay away from the driveways!
"Bad driveways!"
[Roaster guy:] "That's not going to be good for business."
[Jerry-like figure:] "That's not going to be good for anybody."
[Lewis:] "Your roadways kind of develop and grow as your urban area grows from
maybe a rural area or a lesser developed area to a more developed area."
With more businesses comes more traffic volume. Our entry and exit points interfere with mobility.
There's more interruption and high speed might not be safe anymore.
Either we need to cut off access and just focus on moving people--
which is good for traveling, but bad for business--
(By design that's what we do on freeways; there are no driveways on the freeway)--
Or, we just need to give up and just let people have access anywhere they want it.
Seemingly good for business, but very bad for travel-- which makes it bad for business.
When a street has no access control?
Well, those are called parking lots. And good luck driving fast in those!
All that conflict is why parking lots feel stressful.
280 conflict points (just in this picture)!
So, what should we do with these roads in the middle?
Roads which can't be either, but have to be bot.
[Lewis:] "When you put up a raised median, your 32 conflict points go down to four conflict points."
Seem too good to be true? Check this out!
It really does go down to just
four. And the crossing conflicts (the most deadly kind) are almost entirely extinct!
Even add in some U-turns to let people access the other side and we're still
only up to eight conflict points. That's only one-quarter of what we originally had.
By the way, this is the magic which makes roundabouts safe.
It's just the world's shortest median and you just drive in a circle around it.
This reduction in the crossing conflict comes at a big trade-off.
Making a left any place-- was really handy.
Now, we can only do it at controlled places. Business owners may be scared to give that up.
[Business owners:] "We like the old way!"
Even though...
it's a disaster!
There may be practical reasons why you can't install a raised median for the entire block--
but you can protect the most vulnerable part of the street:
the intersection.
[Lewis:] "You know, you know you might have a fast food place right on the corner and someone
daring enough to turn in or out of that
business access right within 50 or 100 feet of the signalized intersection."
[Rob:] "Man, that felt dangerous!"
Because it was.
And there was a police officer watching who didn't care because, unbelievably, that's legal.
Intersections need breathing space. You need room to store
cars that are waiting for a red light to turn green--
Room for vehicles to safely make their turn--
and then merge back together.
These are important places where you don't want cars charging through (like I did).
This kind of extreme conflict has a very high risk of a crashes. That's because people don't
expect you to be turning out so close to a traffic light.
But if we install (even a thin) median curb,
just in the sensitive intersection area, it stops people from going straight or
left out of driveways which are really close to the traffic light.
[Lewis:] "It's been a practice within UDOT to put those shorter strips of raised medians at the
signalized intersections, really to help prevent those gnarly dangerous left turn movements."
Managing access doesn't have to feel like some sort of punishment. It can be fun.
Before the pandemic, I saw how Universal Studios in Hollywood
manages crushing amounts of pedestrian traffic with a temporary raised median.
And of course, there's this...
the most famous raised median...
in the world!
[Radio]
Las Vegas Boulevard is the epitome of traffic control.
You're not doing anything unless a traffic engineer designed it.
Even the behavior of people on foot.
[Rob:] "Look at the lengths they go to take care of pedestrians."
Escalators. Sky bridges. Barriers.
This is a quiet weekday.
The crush of a tourist season weekend makes every piece of infrastructure necessary.
Imagine this street if people could turn left any time and anywhere they pleased.
[sounds of a dying propulsion method]
And raised medians have been here since the beginning.
Hey, you're probably saying, "yeah, but my hometown is not the Las Vegas Strip."
And you're right!
But I did spend the last ten and a half minutes bad-mouthing two-way turn lanes. And so
in their defense--
A study in 1988 looked at the normal roads (ones which don't have a turn lane;
they're just the two yellow lines) and compared them with this.
And found that indeed, there is a significant improvement in safety and in the amount of cars
they can get through. A big reduction in delay on both busy streets and quiet ones.
Now, I asked: Do you think turn lanes are good or bad?
And you replied:
We often forget about trucks. They do a good job of reminding us they're there-- when maybe we put
our landscaping a little too close to the corner and then we come out and find a tire mark in it.
Another viewer writes:
The problem is, a lot of our busiest streets weren't planned. They just sort of
grew up. They just sort of happened.
And they're here now, so what do you do with them?
It can be frustrating because there's no set
standard yet for when to put in a median versus when to put in a turn lane.
The Green Book, which I mentioned a few times, is the bible on highway
geometric design. And it doesn't have a side-by-side comparison
(like a spec sheet) to tell you when you should or shouldn't install one.
I did come across a really good synthesis paper that some researchers put together--
talking about some soft guidelines of when it might make sense
to put in a two-way left turn lane versus a median.
And one of the things they looked at is speed: 25 to 45 miles per hour turn lane works pretty well.
When it's a lower volume street and not one of those big A-to-B thoroughfares
connecting communities the more medium side streets-- you might consider a turn lane.
When there's only two through lanes in each direction--
once you reach three or more, that should be an automatic median.
And when there's no heavy concentrations of left turn traffic--
which they were a little bit frustrated with-- that it wasn't more specific, so they
bugged the Federal Highway Administration.
And they said, well that's when you have more than 60 driveways per mile one every 88 feet, so...
88 feet? That's a pretty close!
Can you imagine miles and miles of a driveways? There and here and there...
Oops, I'm only counting one side of the street.
That changes it to 176 feet. (I thought this looked a little crowded!)
What's really cool though: When you do meet those soft specifications,
a two-way left turn lane can actually be safer than a street with a raised median.
So, it shows that two-way left turn lanes aren't inherently bad.
They're just a tool that needs to be put in the proper place.
I think partly why two-way left turn lanes are tricky; why they're difficult to study--
is because the nature of driveways are so creative and so different.
They're snowflakes. They're absolutely unique.
So, that probably makes it difficult to boil down to a formula.
But one thing's for sure: there are a lot of roads out there that need medians.
And in the next video, let's talk about how to build the median right.
A lot of people hate medians. But maybe it's not because the median is bad--
but because it's a bad median.
See you next time!
[Captions made possible by generous Patreon contributors, like you!]