Navigating Tomorrow: Innovative Road Design Strategies for Safer, Smarter, and Sustainable Mobility
Executive Summary
The United States, with over 4 million miles of roads, leads the developed world in road deaths and accidents. The U.S. Department of Transportation has estimated around 350,000 Americans have died from transportation related accidents over the course of the 2010s. On top of deaths, poor road design costs motorists and governments hundreds of billions in repairs and lost productivity from congestion. Road layouts and design are the source of these issues. The prioritisation of speed and convenience has resulted in American roadways that are expensive, deadly, and riddled with congestion.
Reevaluating our current roadway networks, as well as conventions for transportation planning is key to preventing traffic deaths and bringing the United States in line with other developed nations. A multifaceted policy mix provides the greatest effectiveness for balancing transportation needs and safety, but this proposal explores the specific implementation of road safety through core redesigns such as:
- The Separation of Streets and Roads in Stroads
- Traffic Calming Techniques
A Flawed Road Network
The way to fixing road safety in the United States starts first with reevaluating the way roads are designed and identifying the types of traffic they seek to service. Road layouts are characterised by their levels of street hierarchy. In suburbs, residences are located on winding local streets, accessed only by few connections to arterial roads that quickly move traffic from the neighbourhood to other areas. Street hierarchy is used to prevent traffic from driving through local neighbourhoods, and to quickly move large volumes of traffic over long distances. However, these arterial roads can evolve to become a hotspot for dangerous conditions, both to drivers and pedestrians alike.
The Rise of Stroads
Since arterial roads serve as high-speed, high-volume transportation links, with the main intention of efficiently moving traffic, it comes at a cost of safety and financial productivity. The arterials that cut through neighbourhoods and cities are considered “stroads”. Stroads are a hybrid of two types of thoroughfares, streets and roads. While to many, these words are interchangeable, both are meant to serve different purposes. Streets are designed to be a social gathering place, hosting a safe place for residents to frequent businesses and live on, while roads serve the purpose of efficiently moving cars from A to B, typically between urban centres (Cogan, 2023). This type of layout is ubiquitous in many North American cities today, due to an automobile-oriented transportation system, and the need to move heavy traffic volumes, while at the time providing access to commercial centres. Many stroads have commercial strip malls with ample front parking lined up along the network, some have medians, others have a centre shared, unprotected turning lane. Because stroads try to cater to both the purposes of a street and road all at once, it fails at addressing any need in both. The main reason they fail comes from the amount of access points and unprotected turns in combination with high-speeds prevalent in stroads.
Speeding and Points of Conflict
Stroad speeds limit typical range from around 30–45 mph, however stroad design influences drivers to drive up to 10 mph faster than the posted speed limit (Marohn, 2021, p.21). The long, straight, wide lanes of stroads psychologically instil drivers with a false sense of security to drive well over the speed limit in these areas (Venson, et al., 2022). With high-speeds catering to efficient movement of vehicles in combination with many choke points for rapid deceleration, it creates a hazardous environment for both pedestrians and drivers alike. A 2022 report done by the Governors Highway Safety Association (GHSA) found that 60.4% of all pedestrian deaths happened on “non-freeway arterials,” ie. stroads. In addition to this, the DOT said that “an increase of 10 to 20 access points per mile on major arterial roads increases the crash rate by about 30 percent” (FHWA). Poor access point design also reduces effectiveness of these stroad playing the role of roads, as congestion worsens. This same trend was found for driveway density on arterials. This happens due to the fact high-speed arterial traffic is incompatible with slow moving traffic attempting to enter and exit the stroad to access businesses and homes along the network. Knowing all these issues with stroads, what steps can be taken to mitigate the dangerous driving conditions imposed by this deadly combo of road and streets? Traffic engineers and urban planners have identified various road redesigns that not only improve safety for drivers and pedestrians, but also reduce overall traffic congestion, and increase mobility for all transportation modes.
Separating the Streets and Roads in Stroads
The main problem with stroads is that it attempts to address two needs in one hybrid model; it therefore makes technical sense to separate stroads back into their intended components. Allowing roads to quickly transport vehicles with minimal disruption, and streets to maximise access to amenities, businesses, and homes will drastically reduce congestion, while at the same time, enabling more connectivity within neighbourhoods.
Reducing Conflict Points
Research synthesis on arterials found that average speeds decreased 2.5 mph for every 10 access points per mile. (FHWA) Additionally, regarding crashes, research also shows a strong positive relationship between driveway density and the number of crashes. Therefore, reducing access points to arterial stroads is one of the first ways of streamlining traffic. As previously mentioned: a higher density of ‘’access points’’ and driveways, especially unsignalised access points creates more potential accidents, because as “access points add conflict points, the potential for crashes and incidents involving pedestrians and bicyclists increases” (FHWA, 2006) This is due to the fact that motorists have to quickly enter and exit through access points from the arterials, while pedestrians and bikers are exposed to unprotected crossings that put them in the path of these typically fast-moving vehicles. Reducing these areas of “conflict points,” has been linked to increased safety and improved traffic flow as drivers are afforded more time to react, and provided consistency in driving conditions. This reduction of conflict points turns key stroads back into functioning roads for more efficient and safer throughput.
Balancing Traffic Flow and Accessibility
However, the question arises on how to address the accessibility problem; how will people frequent the businesses located on these stroads if access is cut off? There are a multitude of ways to address this. The first is to consolidate access points/driveways, i.e. having businesses and several properties share the same points. Doing so drastically helps in reducing the amount of access points that need to be connected to the arterial, and thus results in reducing aforementioned traffic and accidents. Similarly, having a collector road or street parallel to an arterial provides the same benefits. These collector streets however have the added benefit of entirely separating the road from streets, thus enabling more local, and safer access to businesses, through slower traffic, and more potential for connectivity.
Traffic Calming
Physical and Psychological Measures
Speeding accounts for almost 1⁄3 of fatal accidents in the United States (NHTSA). The higher the travelling speed of a vehicle upon impact, the higher the likelihood of resulting injuries or fatalities. A study done by the National Traffic Safety Board (NTSB) found that a pedestrian hit by a car travelling 20 mph has a 5% fatality rate; but if that same car was travelling at double the speed at 40 mph, the fatality rate exponentially jumps up to 85% (p.23). While the idea of lowering posted speed limits on these routes seems straight-forward, it simply isn’t enough for motorists. Previously mentioned with stroads, “long, straight, wide lanes of stroads psychologically instil drivers with a false sense of security to drive well over the speed limit” (Venson, et al., 2022). Therefore good road and street designs are better at influencing speed than speed limit mandates. Knowing this, design should induce motorists to self limit their speeds and re-introduce more cautionary driving; this is commonly known as traffic calming. The strategies behind traffic calming uses a combination of both physical and psychological factors to reduce vehicle speeds. Physical traffic calming consists of creating solid traffic barriers, or altering intended vehicle paths that work to slow down drivers. Psychological calming works by putting drivers speed into context for them. Measures ranging from lane narrowing to landscaping, all fall under the scope of psychological traffic calming, altering driver risk assessment and behaviour. In the context of stroads, these strategies are more closely associated with street design, rather than roads. Traffic calming limits speeds, bringing in the role of streets as a complex arena, with lots of multi-modal interaction. This contrasts roads, with than their designs built for maximised flow efficiency.
Physical Traffic Calming
The most prevalent physical traffic calming measures include roundabouts, and speed bumps/humps. But they can also include changing curb radius, or adding medians and islands. These physically force drivers to slow down when driving when approaching these “obstacles.”
Roundabouts
Roundabouts is a tool used as physical traffic calming. They are defined as a circular intersection that diverts traffic from each side into a counterclockwise direction. Roundabouts are successful in both; maintaining a constant flow of traffic, and improving safety compared to traditional signalled and stop sign intersections. They can improve traffic flow due to the continuous speeds maintained by motorists. Since motorists do not have to wait for a signal, they are free to enter the circle when it is clear. While it varies by intersection, this results in a significant reduction in traffic congestion and greenhouse gas emissions from idling. In a cases where roundabouts replaced stop sign intersections in Kansas, Maryland, and Nevada, results showed that they reduced vehicle delays by 13%-23% (Vehicle delays being calculated as the difference between the ideal and actual travel time) (Retting et al., 2002). In New Hampshire, New York, and Washington, replacing signalled intersections resulted in a 65% reduction in vehicle delays (Retting et al., 2006). Other studies have found the reduction in congestion, also results in reduced carbon monoxide (15%-45%), nitrous oxide (21%-44%), carbon dioxide (23%-34%), and hydrocarbon emissions (0–40%) (Várhelyi, 2002). Additionally, even in the case of error, the slow speeds maintained by motorists in a roundabout ensured that there is sufficient time to brake and either prevent a crash, or significantly decrease its severity. Roundabouts eliminate most of the common types of crashes at traditional intersections like T-bone and head-on collisions. Because the flow of traffic is moving in the same direction, these accidents become virtually non-existent. In signalled and stop sign intersections that were rebuilt into roundabouts, the number of crashes dropped by 35%-47%. While roundabouts don’t get rid of all crashes, they do mitigate the severity, with those same studied intersections seeing a larger drop in injuries at nearly 80%. Placement for these roundabouts are relatively flexible. Many intersections benefit from roundabouts, particularity ones that suffer the most from high rates of collisions and persistent traffic congestion.
In the Context of Stroads
The many advantages of roundabouts creates a clear role that they can play in improving road/street safety. Roundabouts provide the perfect transitionary entry points between streets and roads. Since they slow down traffic, it creates safer conditions for fast-moving traffic on roads to decelerate and turn onto streets. Creating these safe “conflict” points is essentially to addressing the stroad debacle, showing a clear division between the two roles of roads and streets to drivers.
Public Opinion on Roundabouts
The only real concerns around roundabouts a part from the construction costs pertain to wariness and skepticism from American drivers. However, studies examining the before and after roundabout construction consistent found that support for roundabouts jumped after implementation (Retting et al).
Additional Physical Traffic Techniques: Adding Pedestrian Islands, Chicanes, & Reducing Curb Radius
Other smaller physical traffic calming measures include ones that change the road layout to encourage further speed reduction, as well as promoting safety for pedestrians. The context of the traffic (on road or streets) is vital in determining which of these measures of implement. But many of these strategies play on calming that typically caters towards low-volume streets.
Pedestrian Islands
Pedestrian islands, also known as traffic or refuge islands, are medians where pedestrians can wait while traversing through difficult crossings. This is usually implemented in wider roads, and lets pedestrians focus on one side of moving traffic at a time. The addition of the curbs or barriers associated with these islands can be used to encourage drivers to slow down and yield to pedestrians (FHWA, 2017). Typically, these islands should be placed where there is a large volume of projected pedestrian traffic or wide crossings that are difficult to cover in one signal, and intersections where there is a high rate of vehicle and pedestrian collisions. Additionally, it is easier to implement this in roads or streets that already have existing medians.
Chicanes
Chicanes are extensions that are used to create curves on streets, thus forcing drivers to slow down in order to safely navigate through. The intensity of the curves could be adjusted accordingly to the desired speed or traffic volume for the street (FHWA). These can range from simple lane markings to physical curb extensions. The considerations for this measure looks at what types of traffic is expected to service the affected streets. Typically, chicanes are most suitable for streets that experience persistent problems with speeding, but lower volumes of traffic, and does not host bus, truck or bike routes.
Curb Radius Reduction
A reduction in curb radius is another speed reducing measure. It works by again, forcing drivers to slow down in order to carry out the tighter right turns. In addition, the smaller curb radius creates safer conditions for pedestrians as it shortens the length of on-street crossing, as well as signalling greater visibility for drivers (CMAP). A general rule of thumb regarding the design of tight curb radii suggests that residential streets have curbs of around 10 to 15 feet to effectively provide speed reduction. In higher traffic areas with truck traffic (more akin to roads), 15 to 25 feet ensures that trucks can clear their turns without too much encroachment into an additional lane (Levine). However, due to the reduced speeds, potential accidents associated with lane encroachment can be lowered.
Speed Bumps / Humps
Speed bumps/humps are the most commonly used method of traffic calming, and with good reason, reducing speeds by up to 10 mph (FHWA, 2017), and accidents by 60% (Tester, et al, 2004). They also have the added benefit of being relatively inexpensive to implement compared to other traffic calming measures. However, their use should be restricted to small local and residential streets where the desired speed limit is under 20 mph.
Site Selection
All these physical traffic calming techniques are used on a as-needed basis. Where target areas identified by city planners or community members have been shown to be plagued with speeding and high rates of collision, or display the potential risks. It is through this process that effective measures and resources can be put into place, and diverted to increasing safety within communities. However into the future, it is essential that these measures be automatically incorporated into plans of new street designs, taking on a more proactive approach that doesn’t reactive respond to a fatality.
Psychological Traffic Calming
Psychological traffic calming differs from physical traffic calming in that it doesn’t force drivers to limit their speeds, instead, it makes them more aware of their surroundings. Through the use of narrowed lanes, landscaping, cameras, and road diets, drivers are able to identify the change from major arterials with high speeds, to shared streets with multimodal transportation and activity, and thus alter their driving behaviour accordingly.
Lane Narrowing
Lane narrowing is one of the tools used to psychologically instil drivers to drive slower. Wider lanes encourage faster driving as motorists feel more comfortable and “safe.” Studies have shown that wider lanes are correlated with higher speeds (Parsons, 2003) and higher rates of accidents (Azimi, 2023). For example, it was found that every 1 ft increase in lane width, led to a 0.4 to 1 mph increase in speeds (FHWA, 2015). Many American roads have lanes set between 10 to 12 feet, with 12 being the standard. In Europe, the minimum standard goes as low as 7–8 ft (Azimi, 2023). Seeing that the United States has 13 road deaths per 100,000 people compared to the European Union’s 6 (WHO), America’s lanes could, and should be narrowed an additional 4 ft each. An added benefit from lane narrow is, not only does lane narrowing promote safer driving, it also frees up additional space to accommodate alternative modes of transportation (Wilson, 2023). Protected bike paths, dedicated bus lanes, and wider sidewalks are all potential uses to fill in the space leftover from lane narrowing, thus allowing multimodal transportation to thrive on the same roadway.
Target Areas for Lane Narrowing
Lane narrowing should be used in areas where lanes are 12 feet or larger, and where the traffic is constantly inter-mingling with other modes of transport. Additionally, it should mainly serve the purpose of bringing traffic speeds down to the intended speed limit, reaffirming that with drivers.
Road Diets
Road diets are the most comprehensive form of traffic calming, implementing a variety of calming techniques that create a safer and higher capacity road. Their effects are similar to lane narrowing, whereby narrow lanes can induce slower speeds, as well as create additional space for public use away from cars. The main component these road diets however are the reduction of overall lanes. Common layouts that benefit the most from road diets are 4-lane, 2-way roads. With a road diet, this 4-lane road could turn into a 3-lane road, with 2 moving lanes, and a central shared lane. While seemingly counterintuitive, reducing lanes could improve traffic flow. There are many instances where 4-lane roads already act in a similar fashion to the 3-lane model; this is due to the fact that vehicles turning left often have to yield to opposing traffic, thus creating a backup of traffic in the leftmost lane. Additionally, vehicles turning left have to cross two lanes of traffic in order to successfully clear the turn. With the implementation of a road diet, not only do vehicles not disrupt traffic flow when turning left, they are only exposed to one lane of oncoming traffic. As a result of the free space created from lane narrowing and reduction, space for bicycle and bus lanes, as well as wider sidewalks could be created, increasing the overall capacity of the network.
Seattle Road Diet Model
An instance of successful road diets include Seattle’s Stone Way North, where crashes decreased by 14%, injuries 33%, and pedestrian crashes 80%. All the while, bicycle volumes increased 35% (Seattle DOT, 2010).
Landscaping
The use of landscaping is another psychological tactic to calm traffic. By planting a variety of trees, flowerbeds, or bushes, it has the multipurpose role; it acts as a physical buffer between pedestrians and vehicles; it becomes a visual cue towards drivers to slow down; and creates a more pleasant environment for pedestrians. However, this type of traffic calming comes at the expense of constant maintenance, but can be mitigated through plant selection, choosing native plants to populate the projects. Additionally, collaborations could be made with local neighbourhoods whereby upfront costs could be paid for by the municipality or leading organisation, while the neighbourhood covers upkeep. This type of deal would be mutually beneficial as landscaping is shown to increase property values and customer patronage (Vibrant Cities Lab). This measure is most suited for streets with high pedestrian and traffic volumes, especially commercial areas where there is constant interactions between pedestrians and vehicles leaving and entering facilities.
Cameras
This traffic calming tool has less to do with road layout but focuses more on the psychological risk assessment with drivers. While unpopular, speeding cameras are effective in reducing excessive speeding. Just the mere threat of a ticket “incentivises” drivers to slow down. Studies found that after the implementation of speed cameras, there was “a reduction in the proportion of speeding vehicles (drivers) over the accepted posted speed limit, rang[ing] from 8% to 70% with most countries reporting reductions in the 10 to 35% range.” (Wilson, 2010) Critics stand against speeding cameras citing concerns over its disproportionate impact on low-income households as many speeding cases happen in lower-income neighbourhoods. However, disproportionate cases of road fatalities also happen in these same neighbourhoods, and such communities are already paying the health costs (Grisby, 2023) associated with dangerous driver behaviour. Therefore, enforcement is necessary to protect the residents of these neighbourhoods.
Successful Case Studies of Road Redesign
Carmel, Indiana
This suburb of Indianapolis is considered the “roundabout capital”, hosting over 150 of them. As a result of the city’s comprehensive approach to road safety, and embracing of roundabouts, crash rates have decreased almost 80% despite the city’s rapid increase in population. In addition to reduced crash rates, the city of Carmel has also seen cost savings from roundabouts when compared with traditional signalled intersections in the areas of construction and maintenance. Carmel residents are also calculated to have saved thousands of gallons in gas as a result of efficient traffic flow, as well as reduced greenhouse gas emissions (IU ERIT).
Lancaster, California
The city of Lancaster redeveloped their downtown main street in 2010, imposing a road diet that reduced the stroad from 5 lanes to 2 lanes. The central 3 lanes were converted into a median that acted as on-street parking, a pedestrian island, and hosted landscaping. Since the conversion in 2010, pedestrians and motor collisions have decreased 78% and 38% respectively. The local neighbourhood has reaped other benefits too, with the street attracting patrons and visitors for the various festivals and markets that now take place on the pedestrian friendly street; this has created an estimated $282 million in economic impact to the community (Steuteville, 2017).
Summary of Recommendations
Reducing the Prevalence of Stroads
- Reducing access points enhances safety and improves traffic flow.
- Consolidating access points/driveways by sharing them among businesses and properties
- Introducing collector roads or streets parallel to arterials provides safer, local access to businesses and improves connectivity.
Traffic Calming Measures
- Physical Traffic Calming utilising roundabouts, speed bumps/humps, Pedestrian islands, chicanes, and curb radius reduction can enhance safety and reduce speed.
- Such measures can be adjusted according to the needs of the road/street.
- Psychological Traffic Calming using lane narrowing, landscaping, cameras, and road diets to influence drivers, psychologically.
- Improving multimodal transportation in conjunction with traffic calming
