Our traffic engineering professionals are often asked about the challenges and innovations shaping the world around us. In our Ask the Pros series, we’re sharing their insights and answers based on their decades of experience to some of the questions they receive.
In this Ask the Traffic Pros edition, we dive into why traffic jams appear out of nowhere, how autonomous and electric vehicles are changing roadway design, and how artificial intelligence is reshaping the way intersections work.
Kevin offers more than 25 years of extensive experience in the field. He specializes in traffic impact studies, parking analyses, and transportation consulting for a wide variety of clients.
Kevin Fellin: The fastest-moving lane is typically the innermost lane next to the median. It’s furthest from friction points like on and off ramps. In contrast, the rightmost lane is usually the slowest due to vehicles constantly entering and exiting the roadway.
Kevin Fellin: That’s often due to the accordion effect, which is a ripple caused by human behavior. Small disruptions like braking, lane changes, road curves, sun glare, or roadside distractions stack up and slow everyone down.
There’s also a limit to how many vehicles a road can handle. Highways typically move about 1,900 vehicles per lane per hour. Once that’s exceeded, flow breaks down even without a crash.
Will has more than 20 years of experience in transportation engineering and planning for a wide range of development projects. His experience includes transit-oriented developments, multimodal traffic impact studies, bicycle and pedestrian planning, freeway and limited access studies, master plan studies, and micro-simulation analyses.
Will Johnson: We follow the Manual on Uniform Traffic Control Devices (MUTCD), a federal guide that outlines when different types of traffic control are appropriate. While it’s not a mandate, it provides standards we use to evaluate intersections.
The decision often comes down to traffic and pedestrian volumes, crash history, nearby schools or rail crossings, and the physical layout of the intersection. For example, if volumes are high and delays or safety issues exist, a traffic signal or roundabout may be warranted.
Roundabouts and signals serve similar purposes but operate differently. Roundabouts naturally slow traffic and reduce severe crashes, while signals can move traffic more efficiently along major corridors. Stop signs are generally used for lower-volume intersections.
Brian Horan: Yes. In many ways, that shift has already started. As autonomous vehicles (AVs) become more common, we are rethinking everything from parking and roadway design to refueling infrastructure.
Brian has more than 15 years of experience in transportation engineering and planning, including addressing transportation issues and using data to create innovative solutions for private real estate developers and public sector clients.
For example, AVs won’t require traditional parking garages. They can drop passengers off, park themselves more efficiently, and leave tighter spacing since there’s no need for door clearance or wide drive aisles.
The broader shift could include fewer people owning cars. Instead, we may see fleets of shared AVs that pick you up, drop you off, then move on to charge or serve another rider. That dramatically changes how we plan for vehicle storage and circulation.
Right now, adoption is still low, but long term the biggest impact will likely be on parking as ownership drops and efficiency rises, we’ll need fewer spaces, better drop-off zones, and new charging infrastructure.
Additionally, AVs could have the ability to be connected to other AVs, like a train or a bus, and roadways might need designated lanes. The important thing to note is that we have a lot of existing infrastructure and this technology will rely on it. Most AVs currently rely on cameras and good signage and striping. Thinking about how we adapt this infrastructure as AVs are adopted is going to be very important.
Daniela brings nearly seven years of transportation design and planning experience to the Galloway team. She is passionate about designing innovative transportation solutions that prioritize safety and efficiency.
Daniela Gonzalez: Electric vehicles (EV) affect traffic design in more ways than people might realize. One key factor is that EVs are heavy and that weight can increase the severity of crashes, especially at higher speeds. This is causing some jurisdictions to re-evaluate speed limits to improve safety.
The weight of EVs also have other implications, like pavement design. Roadways are engineered based on both the number and weight of vehicles using them, using calculations called Equivalent Single Axle Loads (ESALS). As EVs become more common, this is leading to changes in how we design and maintain our roads.
Will Johnson: Absolutely. Crash data is a critical part of traffic engineering, especially when evaluating or redesigning intersections. We typically look at the past five years of crash history to identify trends and determine what can be corrected or prevented.
It’s not just about how many crashes occur, but what types. From minor fender benders to severe or fatal collisions, each crash has its own causes and potential solutions.
Will Johnson: That adding lanes isn’t a long-term solution to traffic. Yes, it increases capacity in the short term, but the benefits are often temporary. We call it the law of diminishing returns. More lanes may ease congestion briefly, but traffic usually fills the added space over time.
In the industry, we’ve known for a while that we can’t build our way out of traffic. Instead, we need to look at creative solutions and understand that we aren’t moving cars, we are moving people, and we need to manage not just the supply side, but the demand side of transportation. Managing the demand involves encouraging people to make better commute choices such as investing in bikes, pedestrian, trains, or bridges connections that matter, plan integrated mixed use communities where you live close to where you work and shop, and employers having flexible work schedules with hours and work from home or incentivizing carpools.
I wish more people understood that widening roads isn’t always the answer. It’s expensive and rarely the silver bullet it seems to be.
Daniela Gonzalez: Yes! AI is increasingly being used to improve traffic signal timing. For example, AI-powered video detectors monitor intersections in real time and can adjust signal timing instantly based on current traffic demand. This helps reduce delays and improve flow, which is great news for anyone frustrated by traffic lights.
Beyond that, there’s also two-way communication between vehicles and traffic signals known as connected vehicle technology. Vehicles send data to traffic signals, which then respond accordingly, allowing the entire network to operate more efficiently. This is different from autonomous vehicles, which drive themselves. Connected vehicles interact with the infrastructure to optimize traffic flow.
Learn more about Galloway’s traffic engineering services here.
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