Road Design: How to Balance Safety, Efficacy, and Traffic Flow

The United States has over 4 million miles of public roadways. Unfortunately, however, 43% of those roads are in poor condition. They cause U.S. motorists an extra $130 billion yearly on operating costs and vehicle repairs.

Poor road design, in turn, is a factor that can contribute to early roadway deterioration. An example is constructing a road without considering potential traffic volume. This can result in the roadway’s constant congestion.

That congestion forces the road to bear the weight of stopped vehicles continuously. All that excessive load can lead to more strain and stress than the roadway can withstand. This can result in the infrastructure’s premature deterioration.

Unfortunately, roads in poor condition can give rise to more motor vehicle incidents.

Thus, for roads to be safe, engineers must design them with efficiency and traffic volume in mind. The guide below discusses ideas that could help them achieve this goal, so read on.

Increasing the Use of Roundabouts

This guide detailing facts on roundabout accidents says such incidents occur less frequently. It also notes how these events result in much less severe injuries.

But how exactly do roundabouts help improve road safety and prevent accidents?

Controlling Traffic in One Direction

Fewer incidents occur on roundabouts because they move traffic in only one direction. Vehicles using these circular intersections must move counterclockwise around the center island. They can’t turn left or right anywhere; instead, they must head toward a designated exit.

Since roundabouts limit traffic to one direction, they can help reduce head-on collisions. They can also be effective in minimizing T-bone or side-impact crashes.

Roundabouts also feature yield signs at each entry point. This gives vehicles already in the circular junction the right-of-way.

Speed Limits and Fewer Conflict Points

Modern roundabouts have a low-speed limit requirement. The range varies, but it’s usually between 15 and 20 miles per hour (mph). So, motorists who plan to use them should slow down before reaching the junctions.

Also, modern roundabouts only have eight conflict points. By contrast, traditional intersections with traffic signals have a whopping 32. Therefore, the former can help drastically lower the odds of vehicle collisions.

Continuous Traffic Flow Accommodates More Vehicles

What about roundabout efficacy? Don’t they worsen traffic congestion or cause delays?

No, because road designers can use them to improve traffic flow capacity. While drivers must slow down and yield to traffic, they don’t have to stop. This allows more vehicles to travel through them at any given time.

Indeed, roundabouts have raised capacity by 30% to 50% compared to traditional intersections. They have also led to an average 89% reduction in delays and a 56% decrease in vehicle stops.

Better for the Environment

Road engineering and design must prioritize the safe transportation of people and goods. However, they can also play critical roles in achieving net-zero emission goals.

Fortunately, designing and applying modern roundabouts can help curb emissions. They can do so because these junctions reduce vehicle idling time. Idling, in turn, burns up to 1/2 gallon of fuel hourly.

All that fuel wasted on idling generates pounds and pounds of greenhouse gases (GHGs). So by reducing such waste, roundabouts can also help motorists reduce GHG emissions. Plus, their proper use helps drivers avoid wasting money on unnecessary gas consumption.

Reconfiguring Existing Roadways

When roads were still under construction, they focused on current and future capacity. For instance, two-lane roads would get additional lanes once their traffic volume increased. These “add-ons” became a standard solution to fix congestion issues.

With the U.S. now home to 275.91 million registered vehicles, it’s no wonder four-lane roads have become the norm. But, unfortunately, as the adage goes, more doesn’t always equate to being better.

This is where road designers can apply roadway reconfigurations, also called “Road Diets.” They often involve projects converting existing four-lane roadways into three-lane segments. They offer many safety and cost-related benefits, including the following.

Reduce Crash Risks

Road Diets help mitigate crash risks by reducing vehicle speed differential.

Let’s use a four-lane, undivided road as an example, where vehicle speeds vary between lanes.

On those roads, drivers often slow or change lanes because of slower drivers or stopped cars. Sometimes, they even weave in and out of the different segments at high speeds. They also have reduced vision of the lanes beside the one they’re on.

Compare that to a three-lane roadway with a two-way left turn lane (TWLTL). In this case, the speed of the lead vehicle in the through-lane restricts the speed of the cars behind. Thus, it also limits the vehicle speed differential.

That reduced speed differential helps cut the risk of vehicle-to-vehicle collisions. Even if crashes occur, the lower operating speed still helps reduce crash severity.

Indeed, a U.S. DOT study found that Road Diets can cut traffic crashes by 29% on average. Moreover, in smaller towns, they can help prevent nearly half of collisions.

Free up Space for Other Uses

Road Diets let road designers and engineers allocate reclaimed spaces for other uses. For example, they can convert the fourth lane into a bus lane. This can be especially helpful for roadways with high volumes of bus commuters.

Another example is to turn a reclaimed space into a protected turn lane. This can help reduce travel speeds to decrease crash severity.

Increase Safety for Bikes and Pedestrians

Reclaimed lanes can also become bike lanes, sidewalks, or pedestrian refuge islands. This can help make it safer for bicycle riders and pedestrians, as these lanes would be for their sole use.

That’s especially crucial nowadays, as 17% of annual crash fatalities involve pedestrians. Bicyclists also account for 2% of crash deaths.

Low-Cost Access Improvement for All Road Users

Road Diets are low-cost improvements since they rarely require new construction. In most cases, they only need fresh paint for restriping. And when converted into non-motorized lanes, their upkeep would also cost less.

Increasing Adoption of Diverging Diamond Interchanges (DDIs)

A DDI (AKA double crossover diamond interchange) is a grade-separated interchange. Its design makes the street traffic cross to a roadway’s other side between freeway ramps. This helps improve the efficiency of vehicles turning left on or off freeway ramps.

A DDI has signs, signals, and pavement markings at the first set of traffic lights. Drivers can cross through the intersection by following these guides.

The left-turn lanes onto the freeway are all free-flow. This means drivers don’t have to brake or stop to access the ramps. Those who need to go straight can do so, provided they follow the second set of traffic lights.

A DDI also has designated walkways and crosswalks. It may also have a lane specifically for bicycle riders.

That said, a DDI is safer than a traditional diamond interchange.

For starters, a DDI only has 14 conflict points. By contrast, traditional diamond interchanges have 26. Thus, the former can help reduce the number of ways vehicles can crash by nearly half.

A DDI can also accommodate more traffic volume than its conventional counterparts. After all, it allows drivers to make a free-flow turn onto the freeways.

Lastly, a DDI satisfies the needs of all road users, from truck drivers to people on foot.

Making More Cycling Infrastructure Available

Cycling infrastructure includes accommodations to enhance and promote bicycling and scootering. They take many forms, from protected bike lanes to racks and more secure shelters. Designers and engineers can place them on roads, sidewalks, and dedicated paths.

But why is cycling infrastructure essential to overall road design?

Improved Road Efficacy and Safety

The more people who switch to cycling from driving, the fewer vehicles on the road. The fewer cars there are, the less traffic congestion they can cause. This can help improve road efficacy for those who can’t bike to work or school.

Cycling infrastructure can also help reduce road accidents since they protect cyclists. This is particularly true for protected and separate bike lanes. After all, they lessen the exposure of cyclists to motor vehicles.

Health Benefits

A protected bike lane or cycle track is a path for the exclusive use of bicycles. It has a barrier separating it from a motor vehicle lane. In some places, that barrier is a parking lane; in others, it’s a line of hedges, trees, or both.

Plant barriers may be more effective in reducing pollution exposure from vehicles. They also help provide cooling and shade to weary, sun-exposed bicyclists.

The addition of protected bike lanes could encourage more people to cycle. This is especially true for riders who aren’t confident in their cycling skills. In many cases, they’re anxious to cycle for fear of getting into an accident.

So by providing safer bikeways, more people can enjoy cycling to and from work, school, or wherever.

Cycling is also a much healthier alternative to driving. This low-impact aerobic exercise can help with weight and cholesterol management. It could also boost cardiovascular function, balance, coordination, and posture.

Environmental Benefits

Bicycles emit low GHG levels during production and disposal. However, their emissions are far lower than motor vehicles.

The act of cycling also doesn’t generate GHGs as it doesn’t burn fossil fuels. For the same reason, this activity doesn’t emit air pollutants.

Those are other excellent reasons road designers should consider cycling infrastructure. Doing so can encourage more people to bike, stay healthy, and be eco-friendly.

Roads Designed for Pedestrian Safety

Unlike drivers or passengers, pedestrians don’t have anything to protect them. This makes people on foot more likely to get severe injuries or die when vehicles hit them. And many of them do; in 2020 alone, over 7,000 died from a motor vehicle crash.

For that reason, designing roads that allow pedestrians must account for their safety. The following concepts can help achieve this goal.

Pedestrian Islands or Raised Medians

The more vehicle lanes there are, the more exposed and at-risk pedestrians are. A raised median or pedestrian safety island can help reduce this exposure time.

Medians are areas between opposing traffic lanes (except turn lanes). Roads with high pedestrian volume can use them as a stopping point. For example, a person can cross halfway at a raised median instead of crossing three lanes in one go.

A pedestrian safety island is a type of median that’s usually wider. This increased size allows for a refuge area.

More pedestrians can stop at this safe spot in the middle of the road. They can cross to the other side once the pedestrian lights permit them.

Curb Bump-Outs

Also known as bulb-outs or neckdowns, curb bump-outs extend the curb into the street. These extensions are for both sides of a road at a pedestrian crossing.

Like pedestrian islands or raised medians, bump-outs shorten crossing times. Pedestrians then have to spend less time making it safely to the other side of the road. This reduces their potential exposure to cars passing through.

Bump-outs also narrow the neck of a street at an intersection. As a result, vehicles turning into such streets must slow down considerably. This required speed reduction then gives drivers more time to spot pedestrians.

Another benefit of bump-outs is they prevent vehicles from parking near street corners. Such behaviors are unsafe, as cars parked on corners obscure the vision of other drivers. Visual obstructions, in turn, can raise the risk of road collisions.

Narrowed roadway lanes also have the added benefit of being aesthetic. For example, they can provide more space for plants, planter boxes, and benches.

Bump-outs can also be low-cost, as they may only need restriping with paint.

Better Road Design for Safer Roadways

From roundabouts to DDIs and Road Diets, all these can help improve road design and efficacy. Most importantly, they let more people safely use roadways by car, foot, or bike. They can also help extend the life of roads and even make them look nicer.

As a bonus, such design considerations can contribute to fewer GHGs and pollutants.

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Libby Austin

Libby Austin, the creative force behind, is a dynamic and versatile writer known for her engaging and informative articles across various genres. With a flair for captivating storytelling, Libby's work resonates with a diverse audience, blending expertise with a relatable voice.
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