I am a design engineer for a municipality in the United States, with a degree in Civil Engineering specializing in transportation systems. I've worked in traffic planning, roadway design, traffic signals, construction, and my current focus is pedestrian safety.

The ins and outs of traffic systems aren't very well known amongst the public, so I'm here to answer any questions you have!

My proof, I've been working from home for several months so unfortunately I don't have anything with my official title on hand.

Edit: 10:30 PM PST

I am crashing for the night, I'll pick it up again in the morning.

Comments: 889 • Responses: 45  • Date: 

rieslingatkos165 karma

Transit studies have shown that the minimum frequency needed to make public transit feasible is one bus every 15 minutes, with one bus every 10 minutes being close to optimal. So why are so many public transit systems, including systems in highly populated locations such as Broward County, Florida (population 2 million) still running buses only every 30 minutes throughout the entire day?

Also, how do you see electric buses and autonomous vehicles impacting public transit? Might we see a larger number of smaller buses running more frequently?

USS_Aayhan273 karma

Budget. More than likely they just can't afford enough buses to run all the routes at that frequency. It becomes a vicious cycle: transit sucks -> nobody wants to pay for bad transit -> transit has no budget -> transit sucks.

Electric and autonomous vehicles could be a blessing or a curse depending on how quickly we can jump onto the train and get a system in place. If we let Elon build it, the roads will be clogged with privately owned Teslas cruising empty to pick up their owner and drive them in individual comfort across town, oh and the owner doesn't want to pay for parking so he just has his empty car circle the town endlessly. It'd be like billions of taxis constantly clogging the roads.

If we get on it early and get it right, minibuses and other micro-mobility options could operate in small scale routes, providing last-mile service from homes to major transit stations.

goat_on_a_float107 karma

There's another reason, too. People who are primarily reliant on public transit tend to be lower income. They don't have the same access to power, they don't donate to political campaigns, and they also pay less in taxes. Transit policies are set by government officials, who are more responsive to people who make more money, have more to lose in taxes if service is increased, and are more likely to donate to political campaigns.

How many millionaires in Broward County, FL are making a stink to their elected officials about poor bus service on a regular basis? Not many.

USS_Aayhan57 karma

Also true. Unfortunately transit infrastructure in the US just isn't going to stick without a pretty big investment, and it's not one that many politicians are willing to make.

Strike_Thanatos28 karma

Also, a lot of wealthy people don't want buses in their neighborhoods. They think it'll let poor people in and rob them, or some shit. This type of person doesn't even want to remember that poor people exist, unless they want to berate someone.

USS_Aayhan37 karma

NIMBYs! The scourge of engineers, planners, and builders worldwide...

Feralbritches19 karma

We currently have rent a scooters or bikes and ride sharing where individuals rent transportation for a period of time, but don't own it.

What makes you think that we're going to own autonomous cars? Wouldn't it be cheaper to rent an autonomous vehicle instead of owning it outright to just circle around?

USS_Aayhan36 karma

It would definitely be good if we did rent our next generation of mobility options, but car ownership remains a pretty big part of the American psyche.

superdrizzle7140 karma

Why arent the lights synced? Seems like a huge waste of resources stopping and waiting at red lights reducing your mpg by half.

USS_Aayhan274 karma

They often are, but maybe not in the way you would think. Coordinated signal timing is very common when signalized intersections are within 1/4 mile or so of each other, but sometimes other factors take priority. Your travel direction may not be as important in reducing congestion as another approach, the signal timing might have been designed for one speed limit but the limit was changed and the timing wasn't updated for budget reasons, or the city council may have even decided not to let the DOT coordinate those signals so stop&go traffic would be encouraged to stop and shop at nearby businesses...

niceguybadboy106 karma

Who was the guy who decided that, between Exits 9 and 8 on the New Jersey Turnpike, there should be about 17,000 miles?

USS_Aayhan180 karma

Oh, that was Roy. He really hates that Crystal Springs waterpark.

sambooka104 karma

In my city there’s a number of very large number of Orange traffic/construction cones. What can cities do to prevent the spread of these invasive cones?

USS_Aayhan307 karma

The key is immediate response. The Great Cone Migration is sweeping across the globe and creating untold horror in our streets. If your city does not initiate an immediate and rapid containment program, you will be overrun.

In my region we have had good success with a widespread trap, sterilize, and release program. The male cones are given an injection that renders them and their offspring sterile. Within 3 generations, the cone population begins to die off. In areas with low risk of collateral damage, we have taken to employing the National Guard to gun down groups of cones from helicopters.

shelf_caribou102 karma

Why are road engineers everywhere so poor at cycle lane design? You seem to manage infinite complexity when it comes to cars, but lose impetus when it comes to bikes.

USS_Aayhan165 karma

Bike lanes are an afterthought in many areas. The focus on individual mobility rather than cars is still a new theory in most of the US.

CalvinsStuffedTiger9 karma

How do we change this? I live in San Diego which is probably the most perfect place in the world for biking as the weather permits it for 300/365 days of the year

Our car traffic problem is getting worse and worse and it’s palpable.

But whenever an initiative occurs to build dedicated lanes, local businesses freak the fuck out about parking spaces and start protesting / leaning on politicians / etc

You show them the data that biking infrastructure actually increases traffic to store vs parking spots and they still think losing parking spots is devastating

These are the same people that complain about traffic and also preach about climate change

I feel like I’m taking crazy pills

USS_Aayhan7 karma

Lobby your politicians, they're for sure doing it. NIMBYs are obstructing progress worldwide, and all we can do it try to talk louder than them.

Emilastus84 karma

How are speed limits decided?

USS_Aayhan142 karma

Typically 1 of 2 ways. Many states and authorities have speed limit laws in place for different classes of roads, like 25mph for a Local street, 35mph for a Collector road, 55mph for an Arterial. Sometimes those laws are for a range of speeds rather than a set limit, or there aren't laws in place, in which case the speed limit is decided by the physical layout of the road and its surroundings using a series of formulas that revolve around the Stopping Sight Distance. We know how quickly you can come to a stop from a certain speed, or your SSD. Based on the visibility afforded by curves or hills on the road, or how far apart business/driveway entrances are, we can set the safe speed limit by that maximum SSD.

ypsipartisan43 karma

Has your state escaped the 85th percentile trap? Tell me your secrets!

For others: the "85th percentile" method used by many states and cities samples the speed cars travel on a road during free-flow traffic conditions, then sets the speed limit to the speed the 85th percentile car is traveling. This ideal condition is then used to set the speed limit for all conditions.

Its a great method for roads that don't experience weather, night, wildlife, pedestrians, congestion, or other complicating factors.

USS_Aayhan10 karma

I've used a modification on it, where we set the speed limit to what the 85th percentile would do, but design for Mr. Reckless.

MechanicalHorse68 karma

Why the hell aren't roundabouts/traffic circles more common? They're all over Europe and they're much more efficient than having stoplights everywhere!

USS_Aayhan152 karma

Roundabouts are fucking amazing and I will make America love them.

However, I will concede that they require more land than a conventional signalized intersection, and can be more expensive. And Americans are just generally resistant to change.

capnvontrappswhistle27 karma

We’ve had four added within our city and two as exit mechanisms from the freeway system. Stupidest things I’ve ever seen. The radiuses are too small. Our area is top producer of winter vegetables in US. There have been a dozen or so toppled lettuce trucks since they’ve put them in. They can’t make the turn; not enough room. Throw in 50,000 snow birds in the winter as well, and our traffic nightmares are increased by those things. Snow birds driving long RV’s get stuck in the circles.

USS_Aayhan67 karma

Good features can't make up for poor design. Roundabouts can easily handle semis and RVs, if you only build them big enough.

MechanicalHorse10 karma

More expensive? How so? Because for light-controlled intersections you need to set up the posts, run the electrical wire, set up the control box, possibly install sensors in the ground, then there's the cost of the electricity to run the lights as well as the time and cost of maintenance, e.g. replacing light bulbs. Isn't is much cheaper to just build the little island and paint around it, then the intersection is done?

USS_Aayhan58 karma

For a low traffic stop sign intersection, sure. For an intersection where you have to have multiple turning lanes, that circle starts getting bigger and bigger real quick.

Land is by far the most expensive part of infrastructure

thechickenfucker-13 karma

You’re not running for office dude. You do work for a municipality. You aren’t going to make America do shit. Just calling you out, fellow CivE here.

USS_Aayhan18 karma

I can still rant from my cubicle

mairabol50 karma

What are some useful technical skills or software packages that would be usecul for an aspiring transportation engineer?

USS_Aayhan65 karma

AutoCAD, particularly Civil 3D, and Excel.

TrumpsBoneSpur49 karma

What's the deal with people that enter the highway as if they have the right of way?

USS_Aayhan199 karma

First rule of transportation, both as a designer and a user: People are Stupid.

The_Law_of_Pizza72 karma

They don't have right of way, but the reality is that you know they are making a difficult merge, while accelerating, with limited visibility out their rear, and a limited runway of space.

Although you have the right of way, you should also attempt to merge out of that lane where possible, or failing that, try your best to yield to them given all of the realities I just mentioned above.

The right of way is not always the right way.

Notpan17 karma

This exactly. I'm a driver by the textbook and a stalwart enforcer of right of way, except with highway on-ramps. I yield to them as they enter, either changing lanes or ensuring there is enough space between me and the car in front of me so the onramp car has room. When I'm the one merging in, while I do my best to aim for gaps, at the end of the day, if a congested highway lane is full of people enforcing their right of way, I'm going to gradually force myself in. I don't see any alternative that doesn't significantly increase the probability of an accident (like stopping at the end of the onramp).

iiiinthecomputer20 karma

Thankyou. Everybody gets there faster and safer if we're predictable but considerate.

It's actually much quicker for everyone if you make room and allow a smooth merge to permit traffic flow to be maintained.

However ... I take exception to people who ignore a totally sensible merge opportunity in order to wait until the absolute limit of the lane then try to wedge in slightly further ahead. Just because they have to be in front. At that point it's merge chicken time.

USS_Aayhan13 karma

If we're approaching a merge and the other car starts to signal that they want to move over, I'm always considerate and let them in. You blow by the whole queue and try to merge right at the end of the lane? Hell naw, I'm blocking your ass in.

pyramidsofmoney46 karma

Who's got it figured out the best? What metrics are you looking at to improve? What cities / routes were most interesting to study?

USS_Aayhan23 karma

The various Nordic countries have such ridiculously low levels of traffic fatalities, it's insane how much more they've got figured out as a society...

For the longest time the metric was vehicle delay, over the last decade the focus has shifted to fatalities with programs like Vision Zero.

ramsayes27 karma

I've had a friend tell me that if there was only one lane in every road, there wouldn't be traffic jams because congestion is caused by people switching lanes. He's full of shit right?

USS_Aayhan74 karma

Merging is the cause of many woes near highway on ramps, but traffic jams will still occur on wide open roads due to the traffic shockwave effect, and intersections. Traffic jams are caused by human reaction times, and can occur any time 2 drivers have to interact with each other in any way.

temp9118 karma

How much would vehicle throughput increase if we had coordinated autonomous cars? Is there some way to take advantage of this technology before they are ubiquitous?

USS_Aayhan48 karma

Probably a lot, one of the main things we have to account for in signal phasing is called Headway. Basically the reaction time to the signal, accounting for the fact that it'll probably take the next driver a second or two realize the car in front of them is rolling and start rolling too.

But if the entire queue could start rolling all together as soon as the light changes? Game changer.

As far as taking advantage of things now, I'm not sure. I'm no programmer, so I don't know how much would be involved, but if cars could communicate with the infrastructure around them and let the controller know how many cars are approaching from further away, the controller could potentially alter its timing pattern on the fly to account for real time congestion.

Specimen19717 karma

When designing new roads (or expanding) for existing towns/cities, what criteria do you use to determine which way traffic should be directed to minimize congestion? And how do you got about implementing the solution? Do you need permits? Who tells you where you can build these roads, and what are some common problems you encounter when designing these roads?

USS_Aayhan40 karma

That is a very contentious answer. Transportation Planning is not at all an exact science, though we tried to treat it that way for a long time. When I was in school, I was taught the Gravity Model. We were given charts that said X number of trips were produced by Y type of housing, Z number of trips were attracted by V type of business, etc etc. So 150 Single Family Homes would produce 210 trips per day in Zone A, and a Retail center with 100 employees would attract 123 trips per day to Zone B. Punch a handful of those numbers in to a few formulas, and you'd get that 165 Trips would happen between Zones A and B every day.

We're now realizing that trying to pigeonhole that way just flat doesn't work. It's a tough field, trying to look at trends and predict the future development of neighborhoods.

99% of the time, it's The Government doing the work. So you get permits from yourself, send a guy down the hall to the Environmental division to make sure you can build there. Sometimes you have to deal with higher level government permits.

The most common problem is getting Right of Way, simply finding the property to build your road on. If I need to add a turn lane to an intersection in a city, there's a pretty good chance I have to put it in someone's parking lot. Buying that land can get very expensive once the landowner realizes they're essentially dealing with a captive audience.

CleanPostingHistory14 karma


USS_Aayhan20 karma

Absolutely, from signal timing to street layout design. I've used software developed by the German PTV Group, their Vistro and Vissim programs, though there is a variety of other software available. These tools let me test road layouts and signal phasing, different types of control, and can fine tune simulations down to the level of local vs tourist drivers and how they'd behave on the road.

Most departments that put out those vids use the planning software to create a simulation of a drive down the road or an overhead view of moving traffic, and are then able to export a file that can be taken by a graphic designer and rendered with high levels of detail.

Feralbritches111 karma

So pedestrian safety... Does this include more green space, increased walkability factors, and bike lanes?

What's your favorite thing to include in any plan?

Are you hired by a community development team(non-profit), by the transportation bureau (government), or a private firm?

USS_Aayhan40 karma

All of the above.

Street trees! Trees can help with traffic calming by giving the impression of a narrower road, causing drivers to slow down, and it's been proven that trees and green space improve the mental and physical health of residents. Good for the infrastructure and the community!

I work for the city Public Works department.

Clash_The_Truth8 karma

It seems like alot of US cities that are expanding or building transit systems right now are focusing on light rail. Do you think light rail is the future for public transit in the USA or will we one day (if there is ever funding...) see future heavy rail projects in US cities again?

USS_Aayhan8 karma

Absolutely, and I hope so. Rail is far and away the most efficient way to move people between centers, the rub is getting development centralized around train stations or solving the Last Mile micromobility issue.

kvtw8 karma

Why do cars get a green arrow at the same time pedestrians get a walk sign? Rarely do they stagger the two. It's like a 'squish now' sign coming on.

USS_Aayhan18 karma

If the traffic volumes are low enough, we can run them both at the same time to minimize overall cycle time, which reduces delays. The cars and pedestrians can be staggered slightly to ensure they have the chance to notice and avoid each other to improve safety.

It's a side effect of peds taking a backseat to cars. When engineers are more concerned with reducing vehicle delay, we run the ped phase at the same time. Personally, I'm a fan of the All-Red Protected Ped Phase. No right turn on red, all lanes stopped, all pedestrians go in their own phase. Minimal conflict between vehicles and pedestrians.

Phil0sophic7 karma

I have seen a flat horizontal piece of aluminum above traffic signals, no wires just mounted above them. What purpose do they serve?

USS_Aayhan8 karma

I can think of a few different flat panels that might be mounted near signals, I'd need more details to narrow it down.

cvertimmunity6 karma

Why cant we have synchronized lights to help flow in rush hour? It's so infuriating to see hundreds of cars sitting at a light for like 40 seconds when there are no cars going the other direction. And right when the traffic is about to make it there the light flips and then they are stuck for no freaking reason.

USS_Aayhan15 karma

We do, in most cases. But it's impossible to plan for every possible outcome and sometimes the traffic just doesn't behave the way we thought it would. It takes time and money that some agencies don't have to update timing patterns, so occasionally it just has to sit and get worse until it's too bad to ignore.

SirNicksAlong4 karma

Is there an advantage to fixed, mass public transit services when compared against a networked fleet of electric, autonomous vehicles operating on roads design specifically for autonomous vehicles?

USS_Aayhan20 karma

Mass transit vehicles will always be more efficient, simply because vehicle size does not scale linearly with passenger count.

JiaBob4 karma

What is the algorithm that decides to switch my lane to red immediately when a car pulls up at the crossing intersection?

USS_Aayhan6 karma

Things like call priority can have a myriad of reasons behind them. The other approach might have heavier traffic so their calls are weighted to quickly clear the queue, or both approaches are so light that they use a minimum of detection equipment and just let the signal run as it gets called.

JiaBob2 karma

The crossing street gets way less traffic, but it absolutely does not wait. I have seen that light turn green as I approach it and turn red again before I can clear the intersection because one car showed up. There is no timing. That lane has a priority.

USS_Aayhan6 karma

My guess would be a completely Free signal, it doesn't care where you are it's turning green when it detects a car.

johning1173 karma

Why do lanes end to become a lain again 1 block later with no change in the spacing or zoning of the area?

USS_Aayhan25 karma

Improvement projects that started on opposite ends and didn't connect for stupid budget reasons.

flukz3 karma

There's a bridge in Seattle, colloquially known as the West Seattle bridge that is closed due to cracks in top spans. What failure in engineering or construction could have caused something so bad it now needs to be torn down?

USS_Aayhan9 karma

The current consensus is that the WSB is failing due to higher than anticipated creep in the pretensioned concrete segments. The sections of the bridge span have shrunk slightly, creating slack in the tensioning cables, and allowing the bridge to sag slightly. As a result the concrete sections are flexing, a type of force that concrete handles very poorly.

ebolainajar3 karma

How do you feel about microtransit?

USS_Aayhan10 karma

It has its place. Last mile service to deliver travellers from a mass transit station to their home or final destination, for example. For long distance movement, it is wasteful.

planetes423 karma

Probably too late:

Can you elaborate on the efficiency of "upstream u turns"? We have several in our area.

Basically, you can't turn left into the main artery anywhere. You have to turn right and then make an immediate u turn (from a pair of dedicated, lighted lanes).

So rather than going through 1 light to turn left, we go through 3-4 (right, u turn, straight through initial, past opposing u turn).

USS_Aayhan4 karma

Turn phases are slow. The theory is that you can move one phase out of the intersection and speed up the overall cycle, turning one busy intersection into multiple slightly less busy intersections.

Personally, I'm not a fan.

RelaxationMonster3 karma

Why aren't cameras/sensors controlling red lights and will they ever?

USS_Aayhan5 karma

They are in the majority of situations.

HonoraryCanadian3 karma

How do you evaluate road and intersection layouts? Is there a simulator program? Games like Cities: Skylines gamify the concept, but I wonder if there's something comparable at the pro level.

Also, what makes a street a good candidate for a road diet? My town's main road is seven lanes wide and would be fine with two if retail driveways every half block and left turn lanes weren't a thing.

Also also, is there anyone that makes a smart traffic light that can evaluate traffic demand and adjust accordingly? A little Tesla-like camera on a few dozen poles and a central AI would seem a cheap way to improve flow compared to road widening.

USS_Aayhan5 karma

There are a variety of simulation programs out there, I've used PTV Vistro and Vissim myself for that sort of thing. I can test layouts, signal timing, even modify driver behavior to see how tourists vs locals would handle the change.

Almost every road could go on a diet. Taking the streets back for pedestrians and cyclists with dedicated transit and bike lanes, wide pedestrian pathways with retail/restaurant space in the outdoors, and more greenery would do wonders for American cities.

We do, but they're fairly expensive and an emerging technology. AI isn't there yet, but centralized Traffic Command Centers that can monitor traffic and alter signal timing on smart, connected controllers are already in place in some major metros.

yashasgq2 karma

How does the traffic light system work? Like how do they decide when to give a green light and where.

USS_Aayhan24 karma

Signal timing is a fascinatingly complex world. Basically, there are 3 types of signalized intersection: Free, Semi-Actuated, and Fixed.

A Freely operating intersection only changes when called. This type is used in rural areas, or at night, when there's very little traffic. Some kind of detector, either an electromagnetic induction loop buried in the asphalt or a camera/radar system, detects a car coming and sends a command to the controller to change the signal to let the car through. The signal just stays green on that approach until another lane calls for permission.

Fixed signals operate on a set timed pattern. These can be used in areas with a little too much traffic for Free signals, but not enough to justify the expense of Semi-Actuated systems.

The most common type is Semi-Actuated. Based on known traffic patterns, the engineer will set minimum green times for each lane, and run a pattern. After that minimum time has elapsed, the green will either run until it Gaps Out and no oncoming traffic has been detected for a certain time period, or a maximum time limit has been reached and it moves to the next cycle.

Which lanes go when, or Signal Phasing, is its own can of worms and revolves around clearing queues in the most efficient way. Again, we look at known traffic patterns and try to estimate projected growth into the future, and determine how much time we need for each lane. We then try to combine those times in various ways in order to minimize the wait for other lanes. If there's a lot of turning traffic, but not quite so much thru traffic, we run a protected turn phase with a green arrow where only the left turn lanes go. If there's a lot of thru traffic but not so much turning, we do a thru phase with a permissive turn(Left Turn Yield on Green or Flashing Yellow Arrow). If there's a lot of both, we'll go by approach, a thru phase with protected turns, so all the northbound lanes go, then all the southbound lanes, etc. Sometimes we run a mix of all 3, there are some very complex computer programs that let us run simulations to try and see what combination works the best.

ClassyButYassy3 karma

can they easily be overridden by an engineer? are they centralized?

USS_Aayhan11 karma

It varies, but a lot of larger urban centers are going to centrally controlled corridors in high traffic areas. Intelligent Transportation Systems, or ITS, is a rapidly emerging field.

In areas with new infrastructure and high budgets, smart controllers can be linked and operated from a central Traffic Command Center. Usually they'll just flip between preset patterns, but sometimes they have more fine control. A lot of areas are running on old controllers though, and can't do central control.

Just about very signal in America can be overriden onsite though. In fact, most controller cabinets have a set of switches on the inside of the door panel so a cop can open it up and manually run the signals.

spderweb2 karma

Can we build a second highway directly over the first, with on ramps in the center? Set the speed limit up there to 120, fully enforced with speed cameras. Set the bottom three lanes as 90 in the exit/slow lane, 100 in the center, and 110 in the left fast lane. If you want to go faster, you move up to the actual express highway.

USS_Aayhan3 karma

Sure, you got the money for that much bridge?

larz_64462 karma

I've heard of this thing called VASCAR: Visual Average speed Computer And Recorder, years ago.

With all the cameras on the highway and what I believe to be inductive pick ups buried in the road; I'll see 2 in each lane. Then a single further down the road.

What I thought was a joke at the time, appears to me, to be real.

Can you shed any light on this? Does VASCAR actually exist? Are these rectangular things that are being buried in the road part of the system

USS_Aayhan4 karma

What you're seeing buried in the road are the inductive detectors for traffic signals. The two closest to the signal are Presence detectors, they tell the controller if there is a queue, the one further down the road is the Advance detector, it tells the controller if a car is coming. The cameras are also often used for signal detection, or just traffic counting to gather data for planning purposes.

VASCAR is a real thing, but is a mobile system mounted in cop cars and aircraft, not in the road.

larz_64462 karma

Thank you for your reply.

The inductive pick ups I see are at traffic lights and on the highway. Usually not to far from a camera. What purpose do they serve on the highway?

USS_Aayhan3 karma

In places where there might be visibility problems for cameras, they sometimes install loops in the highway for traffic data collection. State DOTs like to keep current traffic volume counts on hand for planning purposes.