How Are Highways Designed?

Exploring the relationship between speed, safety, and geometry of roadways.
Although many of us are regular drivers, we rarely put much thought into roads. That’s on purpose. If you’re thinking about the roadway itself at all while you’re driving, it’s probably because it was poorly designed. There are so many factors that go into highway safety, many of which are more philosophical or psychological than pure physics and engineering. But to a certain extent, highway design is an art form.
Watch this video and the entire Practical Engineering catalog ad-free on Nebula: go.nebula.tv/practical-engineering
-Patreon: patreon.com/PracticalEngineering
-Website: practical.engineering
Writing/Editing/Production: Grady Hillhouse
Editing and Direction Help: Wesley Crump
This video is sponsored by Ting.

[@PracticalEngineeringChannel]

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[@kennybiel4832]

I realize you probably don't want to discuss politics, but unfortunately politics plays too large of a role in setting speed limits, even more so than sound engineering principles. You could have mentioned the 85th percentile rule though. That is, in civil engineering, the safest speed on a roadway is the speed at which 85% of the public travels (regardless of posted speed limits) at or below.

[@juantransportador]

Kenny Biel, you are correct, in engendering that is not included, the speed limit in some places is dictated by the police.

[@Ron.S.]

Politicians are the new traffic engineers. Safe? Smart? Efficient? Who cares as long as they are popular

[@DavidLeon140m3]

but yet , last year Panhandle got a traffic light

[@awsaws22]

Please make video about how does steam engine work

[@bobthudpucker7730]

True story: Where I live, the main street is perfectly straight the whole way through the town. It used to have a speed limit of 40 MPH. Then a family whose house was right on Main Street complained about the speed and asked the city if they could lower it. The city looked into it... and changed it to 45 MPH.

[@eac-ox2ly]

Lmao

[@MrNicoJac]

"Because FUCK YOU, this is America baby!" 😝

[@werdnaokczub7021]

Haha! f@#%ing Karen!

[@garrisonsan]

85th percentile speed is usually how the prima facie (posted) limits are set, within certain limits

[@AsbestosMuffins]

did something like this near me, the cops used to have a lovely zone where it went from 50 mph to 35 mph in about 20 feet, now it goes 50 to 40. U don't see them parked at the edge of town that often anymore

[@EstebanFelipe7]

Practical Engineering: There are many factors that come into play when designing a highway My city: We don't do that here

[@koltonkotoski7680]

Your city and my state lol

[@infraprojects3751]

kzbin.info/door/SiaHKyoxSyoc8Rzb2thXJA

[@martymcfly3153]

Why not in virginia they evacuated entire neighborhoods not giving a f*** for a walmart

[@TMacDo243]

@@JackHudler well you can but....

[@kylealexander7024]

@@martymcfly3153 i think u mean walmart bought out all the properties. U dont have to sell.

[@spikeevans1488]

I recall, as a young engineer in the '70s, being told that interstates were designed to hide changes of direction at the crest of slopes to make the road appear straight. Also one of my pet peeves with modern highways are the spirals on exit ramps that sneak up on the driver and all of a sudden they are going too fast; a big problem on a motorcycle.

[@nanszoo3092]

I did that in an 87? T-bird, (one of the last large cars), driving my daughter home from taking her graduation pictures. Luckily that car had a low profile. We did a 270 in the middle of the 2-lane ramp but stayed on the road. She learned a valuable driving lesson that day although I'm not sure what exactly it was. Maybe don't panic and slow down for ramps? There were a lot of trees and stuff hiding the curve. Really. I can't imagine that on a motorcycle. I was on one that wiped out on a flat curve in town once. And I was wearing shorts. Ow.

[@treeguyable]

Never a problem on my motorcycles, just a fun curve, in a county full of straight roads. I have 3 big vtwin cruisers, an R1, and drive a dump truck, and a Hoda Civic. Love the difference between them all.

[@Anthonest1]

@@treeguyable Thats an impressive line up. You a contractor or does a company let you drive the dump truck home?

[@treeguyable]

@@Anthonest1 Just have a little one horse business, but gotta have a dump truck.

[@wta1518]

At least the spirals are always well-signed where I live.

[@ionmaster7873]

Practical Engineering: How are highways designed? Cities Skylines players: Write that down! Write that down!

[@jeffsansome90]

I love Cities Skylines, to be honest I've only played it on Nintendo Switch, but as a Highway Engineer, I cringe at the on-off ramps, the entry and exit angles are waaaay too high

[@tomatosteve3444]

Jeff Sansome dude lmao same I hate when the off/on ramps are unnaturally bendy or high

[@bassdrumflextime1253]

@@tomatosteve3444 me too

[@v13r3r]

@@jeffsansome90 what? You dont slam the brakes from 100 to 20 to make a 90 degree turn on your highways?

[@orchdork775]

@@jeffsansome90 You're a highway engineer?? That's so cool! What do you think about the difference between European roads and American roads? I've read that many European roads have smaller lanes and more curves which requires drivers to stay focused and reduces crashes. How do you ensure that people stay focused when designing highways?

[@jordyhellemons6964]

This man can make anything interesting. He single-handedly brought back my interest in learning about engineering. Legend

[@MukulVyas5]

Soooooo true. I'm a Civil Engineering graduate and due to a monotonous, quality lacking, banal and unfair education system and working culture, I've lost interest but this channel keeps me motivated. I'm so grateful and wish I had a teacher like him. This is how Civil Engineering should be taught.

[@mahdizerrouk5894]

@@MukulVyas5 same here man, i feel you !

[@MarcelinoDeseo]

I'm a programmer, but any work that requires planning and designing excites me and learn from designers of different fields.

[@Phlebas]

I'm an engineering drop-out, so for quite some time, I had zero interest in engineering and pretty much avoided the topic at all costs because it brought back some painful memories. But I'm at a point in my life where I have a satisfying career in a completely unrelated field (archaeology), and I find I can actually enjoy these videos and find them interesting.

[@meenoomeenoo4578]

Same here. Never thought I'd be so amused by learning how roads are made. We took everything for granted.

[@SunlightAldo]

"Not many people think about roads" Me: *a loyal subscriber with post notifications who pesters my friends about why theres cracks in side walks and about all the layers that go into road construction*

[@hedgehog3180]

"Not many people think about roads*" *unless you're a subscriber to this channel then you probably spend hours thinking about a weird highway support you saw.

[@josephjackson1956]

*the average person doesn't think about roads Not the especially observant and smart people that watch this channel ;)

[@mehmetyok8434]

@Flying Speed Brake There are dozens of reasons for it, not that easy. The main reasons are generally badly designed joints and non-uniform base/subbase for concrete pavements.

[@RealZynexx]

ikr

[@BiffaPlaysCitiesSkylines]

I found this extremely interesting :-)

[@himlyk]

Now he just needs to explain roundabout curvature geometry!

[@akinlajanicolasabidemi297]

Lol biffa, I just finished watching your videos

[@badboys174]

I only watch videos like this because of cities skylines lol

[@andrewomboto9458]

What are you doing here biffa?

[@flowersforferdinand375]

Biffa!!

[@rnrtruestories]

man i love your channel. I worked on the design side for almost 10 years for roads and bridges.

[@gameimprovements4347]

Facts.. This channel is amazing. That career you worked in seems pretty sick and underrated

[@THRASHMETALFUNRIFFS]

Whoa... Hella */w\METAL/w\*

[@khiladikumar491]

plzz..share some knowledge as I am going to face lots of interviews ahead

[@kellenpdl]

how did you get started designing roads??

[@khiladikumar491]

@@kellenpdl no

[@mark-ish]

9:17 Draws a perfect moose/deer, contrasted with a brick "car" 😄

[@mbur5099]

According to scale that deer is a BEAST too!

[@booonesaaw]

@@timno9804 basically a Moose

[@michaeljames4612]

😂😂😂😂

[@HarshRajAlwaysfree]

in physics we are too used to assuming moving objects as boxes

[@masudsaleh5155]

​@@HarshRajAlwaysfree9:41 9:42 😅

[@zan831]

In Australia where I live, potholes and kangaroos determine highway speedlimits. Actually almost crashed into a kangaroo whilst passing over a crest as it appeared out of nowhere, just like you said. Thats why I always slow down when I'm going over crests or around tight corners where my sight distance is impeded. It surprises me how fast many people go when they are literally driving blind around these bends/curves.

[@NimithChanceson]

Or just sue the gov if anything happen

[@i_smoke_ghosts]

classic!

[@jonnyso1]

Similar thing in Brazil, potholes determine the speedlimits. Although, instead of kangaroos we need to worry about some dude trying to rob you in some strategic locations of the road, in which case the speed limit goes waaay up, it also determines wether you ignore stop signs and trafic lights.

[@Anankin12]

Don't they teach you that in driving school?

[@Hipcrostino]

@@Anankin12 driver training in Australia is very poor. So most people don't learn this, as their parents who teach them don't know it.

[@jonescg]

I'd love to hear more about railroad engineering - how are new railroad formations settled on? And how do they get the transitions and radii just right? I reckon that would be a fantastic video. Keep up the great work!

[@sublivion5024]

I suggest you look at Gareth Dennis's channel

[@wain___614]

ohhh bro its so cool, i saw one that talked about comparing railway constructions in and the past and present. It was really enticing.

[@stupidburp]

I noticed that the Autobahn in Germany had much longer on and off ramps, gentler curves, more reflectors on the sides, more signage, and a smoother road surface with less pooled water than I was used to from driving in the USA. It showed me that the details of how the roadway was designed could help safely enable faster typical speeds with fewer accidents. I have heard that the driver training in Germany is also more in depth and strict than in the USA which may also contribute to safety.

[@seanthe100]

There's also fewer cars on the road in Germany there's about 500 per 1000, in the US it's over 800 so we have about 60% more vehicles on the road.

[@MegaSnow121]

The Autobahn is in some ways easier to drive on once you realize the rules of driving 100 mph - safely. We were in Germany a few years ago, and I found the Autobahn easy and exhilarating - perhaps it helped that I was a CDL driver in my profession, though my 20-something son did just as well. The Autobahn is MUCH better built and planned than US highways. And safer despite the higher speeds.

[@pleasedontmakememakeupanalias]

@@seanthe100 yes but you are missing the fact that germany as a whole is much more densly populated than the us (7x higher). we have fewer cars per person but still more cars per km of road resulting in much more traffic / more cars on the streets

[@JaredMusil]

You also need a license to play Golf in Germany

[@wouldbfarmer2227]

Germany didn’t have to design their roads with drive-by shootings in mind.

[@MukulVyas5]

I'm a Civil Engineering graduate and due to a monotonous, quality lacking, banal and unfair education system and working culture, I've lost interest but your channel keeps me motivated. Thank you so much :) I wish I had a teacher like you. This is how Civil Engineering should be taught. Thank you once again. :)

[@nickjones0803]

Keep at it brother!

[@MrFranco1198]

Couldn't have said it better myself

[@doggetay]

4:37 "If the superelevation angle is just right, and you're traveling at a right speed, your cup of coffee won't spill around the bend" EUROBEAT INTENSIFIES

[@eshance-0944]

Noice coment

[@froJoss]

Some would say... DÉJÀ VU

[@cmdraftbrn]

the tofu is safe.

[@TheOwenMajor]

GAS GAS GAS

[@RendallRen]

I recognize a reference, but I don't get it. Would one of you kind souls - you, yes you, reading this. Would you explain it to me, please? What is this "EUROBEAT INTENSIFIES" in reference to cup of coffee not spilling around the bend, and related DÉJÀ VU and GAS GAS GAS comments? I too would like to be a cool kid "in the know".

[@visi9856]

As an ex-Road engineer, great video! you covered up the basics very well! Just another thing to add, the transition length for straight to curve is also dependent on the transition length required to transition from crown to Super elevation.

[@austindonley375]

Just took my route engineering class last semester and did a group project where we designed roughly 2 miles of a highway. Way more intricate that I ever imagined.

[@rogerwilco2]

Hills? What is this magic you're talking about? - The Dutch.

[@Julia_and_the_City]

I saw one in Nijmegen once... Wait... Did I? Not sure, might have dreamt it.

[@numericbin9983]

@@Julia_and_the_City On the motorway from Maastricht to Eindhoven, I saw a few hillls. But the slopes were quite gentle.

[@lenny6281]

@@numericbin9983 impossible, you must have been hallucinating

[@terryboyer1342]

@@Julia_and_the_City Kids sandbox.

[@thomasvlaskampiii6850]

But, not all of the nation is below sea level. What goes down, must go up right? Well... I mean when your height is increasing by a centimeter over a kilometer or two, I can see how you'd never notice it

[@blakebiermann4316]

Lane widening in curves is also very helpful when you're pulling a long trailer or driving something wide. Less chance of less skilled drivers getting too close to you

[@jakurdadov6375]

There are design criteria for this. The sharper the curve, the wider the lane. We also consider the frequency of different vehicle types. It doesn't make sense to build very wide lanes for a vehicle that almost never visits the curve. Very wide lanes sometimes tempt drivers to pass where it is unsafe.

[@Baseit]

Love this video: I consistently think about roads and their slopes as I'm driving on them. Thank you for sharing so much of your knowledge!

[@randomgaming2079]

Never would I have thought 5 years ago that I would be a Civil Engineer. And here I am now Sat as an Undergraduate Highway Engineer literally understanding and designing everything that is being talked about in this video.

[@andrebartels1690]

I never cared about civil engineering until I found your channel. Now I gradually start to see the world I live in with different eyes. Thank you for widening my horizon 👍

[@DonyoSanghelei30]

Same. I’m a truck driver and the more I am on the roads and understand their design it makes me a better driver to anticipate traffic changes and better anticipate how other driver are likely to execute certain maneuvers that may be unsafe and allow me time to defensively drive.

[@TheOfficialCzex]

Engineer: "... So, anyway, the most effective speed limit for this section of highway is 75 MPH." The State of Virginia: "35 it is then!"

[@emeltea33]

Highway patrol everywhere, just shooting fish in a barrel. Meanwhile, people drive 50-60 in front of my house where the speed limit is 30 mph.

[@AlwayzPr0]

At least Texas listened

[@TurkishLoserInc]

Entire Northern VA is essentially pegged at 55. Past Quantico going towards richmond it magically becomes 70. I think it has to do with trying to escape DC, if something were to happen, the surrounding traffic would slow down your maximum getaway speed.

[@MikeV8652]

@@AlwayzPr0 Amen to that!

[@speedyme200]

A well-designed up-to-date radar detector would help

[@TheCuriousNoob]

Your series is so interesting and makes me appreciate infrastructure engineers and construction workers so much more.

[@HylianDefender]

4:37 In Initial D, Bunta, Takumi's father, gave Takumi unique training. Every morning when Takumi delivers tofu, Bunta gave Takumi a cup of water to place in the drink holder. Bunta told him he could not spill even a drop of it while he was driving. Besides preventing the tofu from breaking, it forced Takumi to drive very smoothly along the roads.

[@TheAssassin409]

This Traffic Engineer approves this video. although i must mention that set speed limits are mostly political.

[@JustJoshtheDad]

This DOT inspector 2nds that.

[@nicholascrass2555]

Do you then receive a speed limit design requirement and engineer to it? Or are speed limits sometimes set regardless of the road design?

[@imaginerus]

As an electrical engineer, I always get excited to see a circuit I designed assembled on a PCB in reality, even though it doesn't really matter how it looks. I can only imagine how it feels to drive on a road you have been designing for month on your desk!

[@WHYNKO]

In India almost no one respects the set speed limit, it's the geometry of the road that forces us to stick to a certain limit (usually not as per the set limit). Speed limit is only followed within city limits (that too not very well) 😔. But that's India, 😉

[@Numbnuts007]

I've always wondered this, especially since on US highway 19 in Florida which is near my hometown, the set speed limit is 55 mph, but nobody goes that. They either go 60 or 80 depending upon which lane they are in. And if they're not a local, they go 55. I've always wondered why it was 55 when nobody goes that speed limit, and now I have my answer. It's probably political. Why does politics have to ruin everything?

[@ericcheese7594]

+15 during pandemic, -20 during rush hour.

[@captaingreenhat]

More like plus 50 and minus 60 here in austin texas

[@Jorti1boomboxvideos]

75mph speed limit: +40 california day time +70 california night time -100 California traffic

[@ForestFire369]

Bro you can go as fast as your vehicle will take you in an empty 60 zone lmao

[@YagiChanDan]

Try central London.

[@imthedarknight-8755]

T V- I feel like my cops are bored though, I've been pulled over twice for speeding during quarantine when I've been doing the same I've always been

[@EzraEats]

As a recovering truck driver, I absolutely love your videos on roads and highways. I've always loved the interstate system and find all of these nuances so fascinating.

[@SRutcosky13]

ever since i’ve found this channel, i’ve become way more interested in how the world is set up to work. thank you so much, Grady!

[@noonehere4332]

Step 1: design the road to be able to handle 100+ mph Step 2: set speed limit to get maximum revenue.

[@gameonyolo1]

do they teach that in college?

[@ahumandoing6813]

@@gameonyolo1 No, college is for keeping people ignorant. It's not until you get involved in the corrupt workings of government do you learn such tricks.

[@bunchycarter8024]

@@ahumandoing6813 the college you went to was definetly intended to keep people ignorant

[@elizabethwinsor5140]

@jocaguz18 -- baaa! baaa!

[@whiteeyedshadow8423]

@@bunchycarter8024 I am going to remember that flip around burn format for the rest of my life Thanks bud

[@ColinRichardson]

8:44 happened to me in Finland in a rental car. Reindeer were like Ninjas. Popped up out of nowhere. They like to eat the salt on the road apparently.

[@JesusCliment]

In Finland speeds limits are reduced during winter in many roads and highways to account for the ice and the increased breaking distance, to avoid crashes with reindeers and moose. Also, they have experimented with salt statues near the reindeer paths to attract them out of the roads.

[@Mireaze]

Teenage Mutant Ninja Reindeer

[@Triadii]

Why do they like eating salt?? 😂

[@cmdraftbrn]

@@Triadii water retention.

[@ColinRichardson]

@@JesusCliment I was already going way under the speed limit.. Since I was driving on the wrong side of the car, on the wrong side of the road, snowy conditions.. And it not being my car.. I was being super cautious... Thou according to the locals, that wasn't considered snowy.. I guess it's when we in the UK say "this isn't rain" though someone in a desert would call it a storm.

[@skyrien]

This video answered a lot of small questions I've had while driving, but never quite had the motivation to look up. Thank you!

[@w6wdh]

A couple of additional points from a friend who’s a land surveyor. Excess or insufficient fill dirt is an expensive problem. Roads in hilly areas are designed so the volumes of cuts and fills approximately match. Crests and dips are given parabolic profiles with tapers at the transitions, for smooth vertical accelerations, to avoid feeling as if on a roller coaster ride. (I know of a couple of hilly roads that are fun to take fast, for a feeling of partial weightlessness!)

[@Claerti]

"In an ideal world every road would be a straight, flat path with no intersections, driveways, or other vehicles at all. We could race along at whatever speed we want!" Definitely an engineer

[@planetfall5056]

"Look, all I want is for cars to be uniform spheres moving in a vacuum, is that too much to ask!?"

[@kumar1400]

Always look for ideal conditions. Andddd then add all the losses to the equation 😬

[@Speed001]

Speed limit would probably be 1% lighspeed in a vacuum for safety purposes due to human reaction speeds.

[@Speed001]

@@planetfall5056 Wait, why spheres? Hahaha.

[@joeyager8479]

I80 across the Great Salt Desert in Utah comes close to this ideal. 57 miles between exits and mostly straight & flat.

[@filippe999]

The citizens of my city in City skylights will enjoy my newfound knowledge

[@wrex509]

I enforce rigid 90 degree turns. Lol

[@warriorsmustang1784]

@@wrex509 Im not taking any advice from this video. I'm still going to set the speed limits to 120kph with 50 degree bends downhill

[@jaredcadz]

Hahaha! Hilarious! 😂

[@yhoo]

This video is great. Thank you so much for doing this that I, as a lecturer of this subject, can use the link for teaching my students, giving a description about designing the geometry of highways.

[@muhammad.umair447]

As a student of civil engineering i am enjoying it very much salute to your effort and hard work for making such amazing videos

[@Uruduin]

What I'm hearing is no one from the New England area have studied any of this and just did whatever

[@tomsko863]

Add Florida to that list. From looking at a map, you can only conclude that they didn't own a ruler and used a live snake instead when designing their roads. No one cared about sight-lines or efficient design, they were going for this pseudo-flowy feel that makes driving very dangerous. FU Florida. Sink into the sea already.

[@BobSmith-gk9vs]

Nor does anyone in Washington State, some of the worst road designs imaginable.

[@ralanham76]

The town I live in Florida was drawn with the spirograph the roads come off the highway perpendicular at first then immediately start crisscrossing see you can’t even drive straight across town you have to drive at 45° to the left and then 45° to the right and then another couple miles at 90 to the left

[@prestondial1992]

I always though that New Hampshire and Florida has crazy roads, and then I moved to LA and realized that I knew nothing

[@Hyrum_Graff]

David John partly because the original roads were designed for horse powered travel, and any crashes would be at a lower speed and less frequent anyway.

[@maxximumb]

Grady, please could you do a video on why parking lots are designed the way they are. It always seems that they are full of choke points. Is there any actual thinking or design beyond maximum capacity?

[@akonnema]

Omg I think about this topic all the time. It seems like they are designed to be as annoying as possible sometimes. Also I kinda hate walking in most parking lots it just feels very unsafe.

[@edcrichton9457]

Well, depending on where you are, parking lots don't have to abide by same rules as roadways.

[@MrMattumbo]

Worse is the parking garage at my work, it's designed to be driven both ways yet it's not wide enough for two cars to pass at the end of the ramp and people with trucks always decide to park at the edge spots further limiting one's turning radius and vision. It's a fucking nightmare.

[@estellethewhitemage385]

@@MrMattumbo In the U.S. the average cost to build a multi-level parking garage is ~$30,000 per parking space. With a price tag so high, the owner of the parking garage is surely going to design tighter traffic flows to maximize the number of spots. Spots that could be used for high-rise tenet parking spaces, parking for shoppers at a mall, etc.

[@MrMattumbo]

@@estellethewhitemage385 Well this is just an office complex with a few data centers on the site yet they have 5 three-level parking garages packed to the gills with spaces. This wouldn't be an issue but they marked it for two-way traffic even though it has two lanes going up the ramp and a lane on each side of the levels so it could and really should be set up for one-way traffic flow since they decided to make it dangerously tight around the bends. There is literally no way for traffic to pass each other, either someone yields and tucks in or their will be an accident. Right now the place is under construction so who cares, but once office workers start banging up their cars I suspect they'll change it.

[@lesflynn4455]

I discovered this channel today, and it's bloody fascinating. Grady is answering questions turning around in my head for most of my adult life, which I've been too lazy or preoccupied to seek the answers for on my own.

[@tonysuda9066]

Me too.. I've seen the ship crisis in detail and now im more aware that there is so much more

[@sunnymakkar5266]

Hey Grady! I must appreciate this video. Well done on this 👏🏻. This video is an excellent summary of what I studied in my roads and pavements unit in my second year of engineering degree.

[@jadelu2542]

Civil Engineering student here! A year ago, we had our subject "Highway Engineering". One of the big requirements to finish the subject was to build a 25 kilometer road on terrains/ mountains. We had no idea to start the project, and we basically have everything on our own. This video gave a background on how to do it, and can help also others!

[@orchdork775]

Wait, you had to build an actual road, or just design one?

[@OeMpaK]

I play City Skylines, so this kind of things excites me

[@Taladar2003]

Funny, it is the opposite to me, the more videos on urban planning and road design I watch the more shallow games like that feel.

[@ZadieBear]

You want some real fun? Download your Dept of Transportation's Design Manual.

[@daniel_ghax]

Same.

[@EdgeOfCasualGaming]

Great overview. You made me really curious to learn more about how roadway engineers design curves to connect straight sections of roads.

[@jakekrueger104]

As someone who does the drafting on road plans this is a great way to explain what goes through my mind while designing roadways and trails

[@thenotflatearth2714]

UK: our speed limit is 110kph, drivers can drive safely on highways France: our drivers can go a bit faster, 130 Germany: *puts down bong. *now here me out guys*

[@gameonyolo1]

dedass though we should all have that system

[@imthedarknight-8755]

Nikita K yeah I'm not sure why interstates in the middle of Nevada (perfectly flat, no bends, no intersections, long sight lines) even have speed limits. Seems like you could go 120mph just fine, I've certainly done it on worse highways and didn't feel like I was in complete panic

[@05Forenza]

@@imthedarknight-8755 Engineers/politicians could complain all day that cars weren't designed for the speeds. Which is totally false. How many of our vehicles are also sold in Germany? You can't have something deathly unsafe at 130-140mph when that's the flow of traffic. It wouldn't pass their safety tests.

[@user-sq1nc5ot8m]

IMTHEDARKNIGHT - I think it's simply due to the fact that it is so barren. One fuckup and a hospital can't help. Edit - also on two lane highways people have no problem attempting to overtake with oncoming traffic.

[@Stettafire]

@@05Forenza It depends. There are some cars here in the UK that struggle at 70. Toyota Yaris comes to mind, it doesn't like high revs, that car. Also a few others are a bit sluggish. But, you are right mostly, I think. Most cars are capable of driving at higher speeds, it's just a question of the driver and the road. No sense in doing 110 m/h around a tight bend on a country road, but on a motorway? Maybe.

[@mattm7220]

While this was incredibly interesting and very well delivered (as usual), I feel like the video title should be "How Are Roadways Designed?, since he never actually talked about how they use that information to calculate a speed limit for the road. I was really curious about what sort of speed guidelines those different roadway aspects have, yet that was never mentioned. Would love a follow-up to this talking about that side of roadway design - like, how does the radius of a curve affect that safe speed, and does that safe speed change based on that number of curves in a given distance, etc.?

[@emeltea33]

@9:56, politicians determine it, so they can ticket you, at least in Virginia. Huge, descent highways' speed limit: 55 mph. Highway patrol shooting fish in a barrel.

[@StealthNinja4577]

Yea... he can't really do that since the speed limit is arbitrary decided by various communities and politicians. There's a theoretical max speed you can go depending on your driving ability, road curvature, and road conditions. Typically that's way higher than the posted limit. Often this is exploited for revenue with some towns having a couple hundred speeding violations every week for 100-300 a pop. Often it gets capped at 300 because security clearances check for any fine over 300 to work at various corporations.

[@mattm7220]

I didn't actually realise it was so heavily based on politics/revenue that the calculations, and theoretical maximums don't matter at all - though the theoretical maximums based solely on numbers would be really interesting 🤔.

[@StealthNinja4577]

@@mattm7220 yea speeding is really a self correcting problem. People don't typically just live their lives a quarter mile at a time so there's a natural distribution to how fast people will travel any given road during any condition. Usually raising a speed limit decreases the number of tickets issued, accidents stay the same, and accident fatality increases to correspond with the fact you're flying down the road in a metal box faster.

[@Cyberguy42]

I too thought the video did not answer the question posed by its title

[@eljefe62]

In my area, there are two super curves and it constantly amazes me how drivers do not understand that it isn't necessary to slow for them. The posted speed never changes or is warned, yet the majority will slow by 10 MPH as though they are taking a tight flat curve. Taking these curves at the posted speed barely even provides any noticeable centrifugal forces on the body. Great video! I learned about some of these from a roommate who was a surveyor/engineer who had graduated from Purdue. I've never forgotten those things and think about them often as I drive.

[@mischatf]

Been watching one of these videos every day while kicking back after work. Thanks for the great videos Grady!

[@TheDarkKl342]

2:06 You would never put a 100kph speed limit on a city street Russia: hold my beer FYI : in russia you can somewhat legally drive 20 kph over the speed limit. Old road cameras were very inaccurate in detemining car speeds and could even mistake small cars for cargo trucks, so this +20 kph limit was added . Modern cameras are much better, but this thing is still present for whatever reason. This means that one can drive past a camera at 55 kph when the limit is 40 and be fine

[@TheBurzhuy]

Don't tell bullshit. There are no 100+ km/h speed limits on Russian city streets. It is said that maximum speed within any city, town, village etc is 60 km/h. The Government gave people 20 km/h window without fines but it doesn't say that speed limit is 80 km/h. In usual life you wouldn't be fined if you were within this 20 km/h window. BUT for example, if you hit another car and the police found out that you'd moved over speed limit you could be chosen as a person who was the cause of the accident because you've broken the speed limit. In that case you wouldn't get any payments from your insurance company to repair your car but the insurance company would pay to the people whose property you'd damaged and only about $5700 max (third party liability insurance), everything above that value you would have to pay on your own.

[@mmycan]

Formally the speed limit is 60 km/h but we can move with 79 km/h without fine, and even for 99 km/h the fine will be $3,5 with discount. So practically we have some individuals moving with such a high and dangerous speed in our cities.

[@allan9095]

Very similar in Ontario Canada, though I don't know the reasons behind the laws.

[@georgobergfell]

@@allan9095 wasn't a guy going 300kph+ a couple of weeks ago in ontario?

[@LohTec]

In the US it isn't a hard rule, but generally you can go 7mph (11kph) higher than the limit. But if you find someone behind on their ticket quota, they could ding you.

[@nunaoooo]

This is beautiful. Roads in Brazil are generally bad so when I drive in a well built highway, I actually think about how good they are. I love your explanation on speed limits, everyone should understand that. It should be on every class when getting our driver licenses. Instead, we got maniacs driving like they are in a racetrack, putting everyone else in danger.

[@DriveI65]

I spent most of my adult life involved in road design and your explanations are spot on.

[@4IN14094]

"Your cup of coffee won't spill at all around the bend" *Eurobeat intensifies*

[@ryleyh1185]

"Roads rarely traverse areas that are perfectly flat" Nebraska - "Am I a joke to you?"

[@bobthecannibal1]

On the highways and interstates, sure, because "Good placement by highway engineers". When you get to the more local view, though, there's elevation and hills due to river valleys.

[@HarmanRobotics]

I guess you haven't been to Nebraska, maybe you were thinking of Florida?

[@mirzaahmed6589]

Nebraska isn't flat.

[@DestanyBrown]

I drove through Northern Nebraska and it's rolling green hills!

[@utetopia1620]

Funnily enough, of the 5 longest straight stretches of road in the world, none are in Nebraska. I once drove the 90 mile straight in Australia. It kinda kinks at the end, then continues on straight. Thats just because they started building it from each end, and were slightly out by the time they met up, so they had to do a bit in the middle to reconnect them!

[@miguelagawin]

Thanks for this great content! Just drove the Trans-Canada Highway and did notice how experience must’ve been considered by the engineers. This appreciation makes me want to take on more road trips to find such treat communicated by the designer where it’s not just reliant on the scenery. If anyone has tips, please share.

[@AliceHollend]

"Here's how a perfectly designed highway is made." Russia: "Hold my vodka while I dig some more potholes"

[@nittygrittytalks5999]

Russia: "let's fix some asphalt in winter to make driving even more enjoyable"

[@F3Ibane]

Grady: On today's episode we're talking about roadway geometrics and the shape of highways. Me: *F#&k yes, we are!*

[@Serahpin]

"In curved sections, engineers make the outside edge higher..." Driving through Georgia, I've found many roads where the outside edge is _lower_ and you feel like you're going to fly off the pavement.

[@anzman911]

That's a safety feature, so you don't drive too fast 😂

[@cuttingcut1321]

I never had the faintest idea that so much work goes into building roads : O .... and you explained them so easily!! Thanks Grady and Pls continue the series if there is more to learn🙏🙏

[@chaotcmind]

This was my Road Construction class summarized in 12 minutes lol

[@mureithikivuti]

IKR. So weird!!!!

[@Racingboom]

I’m still so amazed how little subs Grady has with the quality and variety of content he creates.

[@IainHendry]

Your explanation of spiral transition curves is the best I've ever heard - thank you! These are used in railway and roller coaster design as well.

[@MegaSnow121]

Fascinating video. I did not know how much goes into designing a road, and loved learning more. If you have ever driven on I-5 northbound or southbound just south of downtown Portland, Oregon, you drive through a bad stretch of highway called the Terwilliger Curves, a short stretch of sharp curves with three lanes of traffic in each direction. The curves were built before more stringent regulations were in force, and, though the state has made improvements, frequent accidents still happen. I would love to hear your take on this appropriately 1/2 to one mile stretch of I-5.

[@fraserhocks7859]

Love your channel. Great to see this, as a geometric engineer (road designer) with over 30 years under my belt, Iv finally found a link that I can point people too when I try and explain what I do for living 😁. You beautifully described, in simple terms the complex nature of geometric design of road, far better than I could have myself (id bore you to death 🤭). You even discussed operating speed versus posted speed... Outstanding! Despite so many years in the industry, I constantly find it interesting the influences of geometric design and roadside features, on driver behavior.

[@jack1954]

Really enjoying your series on roadways so far. I really appreciate how you go into detail about all the different aspects of roads. 👍

[@UrFavSoundTech]

There are two sharp 90° turns by my house. I can normally see the whole turn. But the corn is near full height in the fields next to it.

[@ncot_tech]

There's an off-ramp near here that merges with a regular road on the "wrong" side (I'm in the UK, we drive on the other side of the road, side roads always merge from the left. This one merges from the right). If they've cut the grass on the side of the road it's easy to see any cars coming, but when the grass is long it's possible for even small trucks to get hidden until they suddenly appear from nowhere.

[@moonasha]

this happens near me but with cattails. Gotta basically pull into the road to see

[@visi9856]

Roads with low design speeds can have sharp turns. They don't even need to have superelevation

[@admiralcapn]

8:08 - "I'm...pretty tired...I think I'll go home now."

[@tommypeake3274]

Grady. Thanks for these videos. I use them in my PLTW Engineering Essentials intro class when covering urban design

[@Nveas15]

What took me a whole semester to grasp has been revealed to my mind in just 12 min.. awesome content mate! Keep it up ;)

[@theondono]

When a civil engineer has a better oscilloscope than you do at your work as an EE 😭

[@lavitaebella6561]

I am from Romania, I am 19 and I bought last year an oscilloscope for 500 euro. It is a Siglent SDS 1104X-E.

[@EvilSandwich]

I still use a phosphor tektronix from the 80s that I got second-hand when my high school was going to throw it out for a much more advanced model. She still serves me well but I'm also just a hobbyist LOL

[@terongkun]

Man u make good video for learning about road making, not only about explanation but also those ilustration, nice montage and the way you explain it are as good as my professor teach on class Hope u can make this more often, good job

[@1linkbelt]

Your channel is of special interest to me, since I supervised highway construction with a state DOT for 30 years.

[@JeffDG]

"based on terrain, traffic, existing obstacles, and of course, safety" You missed a critical factor...the local government's need to collect revenue from speeding fines...oh, wait, that's not the engineers who do that one...nevermind.

[@crisu1072]

You should get the day find system lol

[@LMacNeill]

How are speed limits set? Government official: "We can extract the maximum amount of money from the peasants by setting the speed limit to 55 and handing out tickets like candy." Engineer: "This road is designed to safely handle traffic at 80 mph." Government official: "Ok. 55 it is." Engineer: "But..." Government official: "Like candy..."

[@raymond289]

55 mph 90km/h comfortable for old Grandpa and Grandna on Highway. Including if 1 or 2 car suddenly breaks down. motorist get enough thinking time to move OVER. easy to manage construction on the road. Low Speed Limited Dangerous points People drive Sleepy some people clam unable to Operate at 75 mph 122 km/h. Faster Highway Longer Off ramps and Extra right lanes. Prefers a Off Ramp Dividers. Faster Highway required to have 2 speed limit Car and Truck speed limit. Truck brakes distance required 3.5 uoward 9 x distance to stop. Compared to a car at same speed. North America Canada & USA hand out license to anyone able to walk. You don't see European countries crash cars as much as Canada or USA. Strict driver license standard. Farm style driver licence system. Not everyone live in Horse Town or Horse City. This is numbers Reason of Car Accident Accountability on Driving School, license Systems.

[@josephburchanowski4636]

@Paul Kian Long answer short. US highways aren't actually designed for 80mph speed limits. As there are other designed requirements that would be used if such were the case. . Also there are a number of factors that make 80mph speed limits less safe than 55 mph speed limits. Such as lax driver license tests, old people, sleepy people, construction, cars breaking down, and more.

[@Randomguy-ch6je]

There’s a road near where I used to live that’s divided like a freeway and designed for 45mph. It has a 25mph limit(used to have 35). The cops love it. I can barely go 30, the road just encourages speed.

[@Puckosar]

Ya you hit the nail on the head with that one

[@mjc0961]

@@raymond289 "North America Canada & USA hand out license to anyone able to walk." Dude, I wish North America was that strict with handing out licenses. Might be a few less idiots who come to a near complete stop before a simple 90 degree right turn. Maybe less idiots who think it's cool to drive in the middle of the road when there's no painted lines, too.

[@Beryllahawk]

Very interesting! I spent a lot of time on highways every summer as a kid (having family all over Texas makes for great road trips) and as I've watched this series so far I can visualize so many places on those routes from years ago that illustrate exactly what you're talking about. Would like to add a small note - the curvature on a road can be really important for non-car traffic too. Being on a bicycle and trying to make a turn too tight - ouch! Hills can be a literal pain too. I am glad that some cities and towns are beginning to make their roads less car-centric, friendlier to bicycle and foot traffic. It won't be a quick process, goodness knows, to get the US to kick the automobile habit as it were. But already I feel like civic engineers are rising to the challenge of providing good ways to help it along by giving us excellent travel paths for other modes of transportation.

[@bgw33]

Kudos. The narration script is so very good. Easy to follow and is well conceived. While watching I was struck by how similar editing a video must be to highway design. Substitue viewer for driver.

[@sergeant5848]

You said "Centripetal Force"- Oh Grady, I love you! You are a true Engineer.

[@suhaskodali8707]

"Engineers follow guidelines on curves to make sure they are sufficiently gentle" Massachusetts: we do what now?

[@vineetnagavi3689]

Clearly explained, and all points explained so beautifully 👍

[@Blobby_Hill]

Fascinating video, Paul. Thanks for sharing.

[@croman478]

I’ve always wanted to be a road/ highway designer. I constantly look at the roads and highways I drive and think of better systems. Maybe in the next life. Thanks for the video.

[@reggiep75]

0:26 - Arrgghhh the YT compression soup.. As for your good video, and me - a procrastinative critical thinker, I think way too much about things like this and the justification for the way things are and often end up speculating loads without reaching a solid answer and yet my thoughts were 90% right. It's nice that I can tick this off.

[@midwayj72]

Nice. I would have added the assessment of balancing cut and fill when looking at a project overall, together with deciding on bridges or tunnels when evaluating vertical alignment.

[@rishalprasad9721]

Such a well explained concept. Thank you so much.

[@Julia_and_the_City]

Brady, an engineer: "in an ideal world every road would be a straight, flat path with no intersections, driveways, or other vehicles at all. We could race along at whatever speed we want!" Me, an urban planner: "well yes but actually no."

[@hoguemr]

*Grady

[@user-bl4oq7fd8d]

Me as a German: "well no but actually yes."

[@MsDangerousBeans]

Me, a motorcyclist: "oh hell no!"

[@RusticKey]

Me, as a pedestrian: Well, yesn't

[@jmbpinto73]

NO, i like the variety of landscape and to do my driving along the way.

[@This_Is_Not_My_Username]

Allll of this work that went into finding the perfect speed limit by an engineer to be 55mph. Then the city comes along and slaps a 35mph speed limit on there as a speed trap.

[@Eggwood_]

55mph is only good in america in the netherlands its saver altough i can ride 100 mph

[@superandreanintendo]

In 12 minutes you resumed all the stuff I learned in the last year of surveyor school. Well done

[@federicotrupiano3902]

This is the best channel answering the best questions i never came up with

[@ricardomilos2674]

Engineer: *think so hard for speed limit* Me: Deja vu

[@RobertMilesAI]

10:45 "As safe for drivers as possible" This would seem to neglect the importance of considering the safety of non-drivers in road design

[@Stettafire]

I think that's typical of the American attitude to roads. Jaywalking laws and such do not exist in my country. Drivers are expected to pay attention and give way to pedestrians.

[@ThePhobophile]

This video is about highways and interstates, which don’t necessitate designing towards pedestrians or any other non-vehicle traffic. They aren’t concerned with the safety of non-drivers because non-drivers aren’t going to be the ones using them.

[@esdgolf323]

Bicycle facilities are considered in most highway designs. They may not make it into the finished product for various reasons (right-of-way costs, construction costs, etc.). Pedestrians are not really considered in highway design except for at intersections. Pedestrian safety is dealt with in traffic engineering regularly (timing of traffic signals, pedestrian only crosswalks, etc.).

[@orchdork775]

@@esdgolf323 I've never seen a bike lane on a highway before... There's just no way a cyclist could go fast enough. Where do you live that has cyclists use the highway?

[@esdgolf323]

@@orchdork775 I'm using the term "highway" to describe normal roads you see everyday. I am not talking about freeways, expressways, or interstate systems (limited access roadways).

[@ronaldmaneja9948]

Well done for summarizing highway geometric design

[@czr16]

Watched this while on a road trip. I can never look at roads the same again thank you!

[@oracleoftroy]

You forgot the part where they figure out what the safe speed is and then lower it by at least 10 mph and build a speed trap so they can poll tax drivers.

[@reidcushman3562]

One of the things I love about this channel (and others focused on the engineering all around us) is reminding us how complex are the "simple" things we take for granted.

[@scottsthaname1]

The roads where I'm at are great... the way you contour from one curve to the other without having to slow down even when pulling a trailer and the steep down slopes go into long straightaways to ease brake usage... engineered art.

[@kyawhlakhoin2262]

Distinct descriptions feel easy to follow. Thanks.

[@dennisdeng3045]

I wonder if there's a video on the geotechnical aspect of road design too. It's important to know what lies beneath the proposed route.

[@rancidmarshmallow4468]

it would be great to talk more about the intersection of engineering and the other disciplines and politics surrounding it, too! the way roadways are designed is fascinating, but the speed limits, routing, and standards are all mostly set politically, and the constraints on the most heavily traveled freeways come from urban geography, not terrain!

[@kehdi737w]

Always wondered how this is done! Came across your video and loved it! Awesome 🤙😃

[@JulianShagworthy]

This is insanely interesting, and I've noticed whenever there's a lack of 'spiral entry' into a turn without actually realising it - I automatically position myself at a greater radius (edge of the lane) on entry, then use the width of the lane to gradually meet the radius of the turn. I see lots of people doing this, probably without realising :)