Читать книгу Confessions of a Recovering Engineer - Charles L. Marohn Jr. - Страница 18

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 by speed limits and signalized intersections. The turn lanes and wide curb radii make movement easy, yet getting from one building to another often requires lengthy detours, U-turns, and delays. There is a veneer of safety that comes from having plenty of margin for error built into the design, but the complexity of the environment creates an underlying tension that randomly disrupts the comfort.

While engineers have tried, it is impossible to make a stroad safe. State Street in Springfield has one of the highest crash rates in the state of Massachusetts.⁴ The only way to improve safety on a stroad is to convert it into a street or a road.