but does not stop anywhere is merely an exercise in frivolity. Connecting one place to another is the minimum threshold a road must meet to be truly viable. That viability, however, will ultimately manifest, and be measured by, the wealth created in the places that it connects.
Roads and streets are yin and yang for city building. They are at cross purposes and antithetical to each other, but both are necessary for ultimate success. We must have great roads that provide high-speed connections between productive places, places that build wealth and prosperity. We must also have great streets that produce enough wealth not only to sustain themselves, but also to fund a proportionate share of the roads that connect them to other productive places.
Degrading roads to make them more street-like, or degrading streets to make them more road-like, reduces the overall value provided by the transportation system.
Thinking of roads and streets in terms of the value they provide, the functional classification chart in Figure 2.1 should be replaced with the chart shown in Figure 2.2. The chart provided in Figure 2.2 places speed along the horizontal axis and value along the vertical, answering the question: Where do transportation investments provide the most value?
Figure 2.2 Which transportation investment provides the most value?
The greatest value is provided where speeds are very low (street) and where they are very high (road). We get the most value from our transportation investments when they are used as the framework for building a productive place, or when they are used to move quickly between productive places. The further an investment strays from these objectives, the less value it provides.
There is a large amount of space in the middle of this chart where increasing speeds reduces value. Once speeds exceed 15 or 20 miles per hour, traffic is moving too quickly for a place to really thrive. Value does not start to be created again until speeds get up above 55 miles per hour; the point where the transportation investment is providing a meaningful level of mobility.
State Street exists in that middle space, as does nearly all of what has been built on the North American continent over the past century. In the classification system of the engineering profession, these are generally called collectors or arterials. I have taken to calling them stroads.
The Stroad
A stroad is a street/road hybrid. It is the futon of the transportation system. A futon is an uncomfortable couch that converts into an uncomfortable bed, something that performs two functions but does neither well. A stroad tries to be both street and road, providing both mobility and access, yet fails miserably at both.
If you are traveling in an automobile faster than 20 miles per hour, but slower than 55 miles per hour, you are most likely traveling on a stroad. Stroads have the wide driving lanes, turning lanes, recovery areas, and other features used to facilitate high speeds on roads. Despite this large investment in asphalt, concrete, steel, and land, nobody is legally allowed to move fast along a stroad. They are typically designated for speeds between 30 and 45 miles per hour, with frequent traffic signals that inflate travel times by stopping traffic entirely.
A stroad also tries to function like a street and provide a platform for building wealth. By providing access to homes and businesses, a stroad creates an environment where individuals and the community make investments in property with the expectation of a return. Yet, because of the speeds, development on a stroad tends to be spread out, which increases the cost of infrastructure and other public services and decreases overall financial productivity. I will discuss the dynamics of financial productivity for a street in more detail in Chapter 6, “Traffic Congestion.”
Stroads squander community wealth. They are significantly more expensive to build than a street. For the level of investment, they have a comparably poor financial return and fail to provide a meaningful level of mobility. Yet, the financial impact is far from the only price paid for building stroads.
Stroads are the most dangerous environment we routinely build in our cities. If we applied a fraction of the level of scrutiny to their design that we have to the design of such items as baby carriers, lawn mowers, or beach toys, we would have made radical reforms decades ago. Thousands of people die each year on stroads, with countless more maimed and permanently injured. This happens for reasons that are not difficult to discern.
Stroads facilitate traffic speeds that ensure a high frequency of violent collisions. A collision with a change in speed of 30 miles per hour can result in a severe traumatic brain injury for the driver or passengers, an AIS-4 on the Abbreviated Injury Scale.2
For people outside a vehicle, the average risk of severe bodily injury (AIS-4) jumps from 50 percent at just 31 miles per hour to 75 percent at 39 miles per hour. The average risk of death for a person outside a vehicle jumps from 10 percent at an impact speed of 23 miles per hour, to 25 percent at 32 miles per hour and 50 percent at 42 miles per hour.3 Obviously, age and health impact an individual's chances of survival, but horrible injury and death are common at speeds that are routine for stroad environments.
On roads the speeds are much greater, but they are achieved in a simplified environment that generously corrects for routine human errors (see Chapter 3, “Whose Mistakes Do We Forgive?”). In contrast, stroad environments have all of the complexity of streets. There are vehicles randomly stopping. There is cross traffic. There are vehicles that make 90-degree turning movements. There are vehicles randomly entering the flow of traffic and there are others that are randomly exiting it.
In auto-based transportation systems, randomness is the enemy of safety, especially as speeds increase. With hundreds of millions of people driving through stroads each day, some of the randomness results in high-speed collisions between two or more vehicles, or between a vehicle and a person outside of a vehicle. The complexity of the stroad environment makes this kind of tragedy inevitable.
For people walking, biking, or using a wheelchair within the stroad environment, the risks are even greater. A person on a sidewalk has no defense at all if a vehicle leaves the roadway at stroad speeds. The person crossing the stroad is even more exposed and vulnerable. That is true even when they cross at designated places and at specified times.
Stroads magnify that vulnerability by making it necessary, yet difficult, to cross. When Sagrario Gonzalez left the library on the evening of December 3, 2014, it was necessary for her to cross the stroad in front of her. Her car was parked where it was supposed to be, in the designated library parking lot on the opposite side of State Street.
While State Street is a street, it is not designed like one. It is also not designed to be a road. State Street is a stroad, so it is designed primarily to facilitate traffic flow at high speeds during peak times while also providing a modest framework for places like the library to exist.
This means that there were four wide lanes to cross with no sanctuary anywhere in the middle. It also means that the traffic signals, the only place where Gonzalez could have crossed with some assistance, are spaced out and timed to keep traffic moving. All of this makes a simple thing like walking to the car frustratingly difficult.
The irony is that stroads are frustrating for everyone, including drivers. Someone driving a stroad is continually presented with mixed messages. The wide and forgiving scale of the design is throttled back artificially