Why “forgiving roadways” are not the solution in urban areas
Roadway designers since the 1960’s have used the concept of “forgiving highways.” This design philosophy attempts to “forgive” driver error on interstates and freeways by providing wide, obstacle-free clear zones, burying the end of roadside guardrails and flattening or rounding slopes and ditch sections. Due to its success in reducing fatal crashes on high-speed, access-controlled roadways, engineers have been applying this methodology to urban streets in built up areas as well. A recently released AASHTO document entitled “Keeping Baby Boomers Mobile: Preserving the Mobility and Safety of Older Americans” focuses on reducing fatalities amongst the elderly by applying forgiving highway principles to all roads. It recommends “widening lanes and shoulders to reduce the consequence of driving mistakes.” However, this approach might actually make certain roads deadlier for motorists, as it encourages drivers to drive faster and less cautiously. Evidence also shows that pedestrians and bicyclists are much less safe when roadways are optimized for drivers.
Recent studies have shown that the key to safer non-freeway roads is slowing down speeds appropriate to context. Research by Eric Dumbaugh of the Texas Transportation Institute has shown that at least in dense urban areas, less “forgiving” design treatments — such as narrower lanes, traffic calming measures, and street trees close to the roadway — appear to enhance a roadway’s safety performance when compared to more conventional roadway design. Engineers in the Netherlands have been designing their roads in urban built-up areas to operate more slowly and have since seen a 75 percent reduction in fatality rates.
The AASHTO recommendations aim to lessen the consequences of vehicle departures from the traveled way, but they do not actively try to prevent their occurrence. These measures also encourage automobile dependency amongst older drivers instead of providing non-driving mobility solutions. In contrast, the Federal Highway Administration has produced a website which highlights scientifically proven safety-focused countermeasures which include slowing down traffic through the design of narrower roads, roundabouts, and corridor access management strategies. These measures are context-sensitive and proactively seek to prevent driver error.
In urban areas the concept of forgiving highways is not cost effective and requires larger right-of-way areas in environments where land is particularly scarce. It is therefore incumbent upon today’s engineers to recognize that urban roadways must be treated as multimodal corridors where accessibility is prioritized over vehicular mobility. Design manuals such as the AASHTO Green Book and the Roadside Design Guide must not be treated as inflexible, and engineering judgment must be used to produce context sensitive designs. In addition, several states have produced street design guidelines which allow for complete street, context sensitive, and locally specific design solutions which enhance safety and community function. Some examples are The Smart Transportation Guidebook, New Jersey and Pennsylvania DOT, Urban Street Guidelines, Chalotte, NC, Street Design Manual, New York, NY and the Better Streets Plan, San Francisco, CA.