Low-income communities are significantly less likely to have access to parks and other opportunities for safe recreational walking and are less likely to have sidewalks, marked crosswalks, and street design to support safer, slower speeds. Lower-income neighborhoods are also much more likely to contain major arterial roads built for high speeds and higher traffic volumes at intersections, exacerbating dangerous conditions for people walking.
Provision for adequate drainage is of paramount importance in road design and cannot be overemphasized. The presence of excess water or moisture within the roadway will adversely affect the engineering properties of the materials with which it was constructed. Cut or fill failures, road surface erosion, and weakened subgrades followed by a mass failure are all products of inadequate or poorly designed drainage. As has been stated previously, many drainage problems can be avoided in the location and design of the road: Drainage design is most appropriately included in alignment and gradient planning.
In addition to considering intensity and duration of a peak rainfall event, the frequency, or how often the design maximum may be expected to occur, is also a consideration and is most often based on the life of the road, traffic, and consequences of failure. Primary highways often incorporate frequency periods of 50 to 100 years, secondary roads 25 years, and low volume forest roads 10 to 25 years.
Inadequate outlet design. By constricting flow through a small area, water velocity (along with its erosive power) will increase. Outlets need to be properly designed in order to withstand high flow velocities and thus avoid excessive downstream erosion and eventual road failure.
Cross ditches or water bars, are typically used on temporary roads. They are the easiest and most inexpensive method for cross drain installation (Figure 83). However, they impede traffic, wear out quickly, and are difficult to maintain and are, therefore, not recommended except on very low standard roads. In order to be effective, the cross ditch should be excavated into the mineral soil or subgrade and not just into the dirt or surface layer. Water bars should be installed at a 30 degree angle to the centerline of the road, and ditch and berm should be carefully extended to the cut bank in order to avoid ditch water bypass. A berm should be placed in the cut bank ditch to divert water into the cross ditch. Care should be taken that the berm and ditch is not beaten or trampled down by traffic or livestock.
Hurricane Sandy caused flooding in New York City subway stations in 2012. Source: USGCRP (2014)High temperatures cause rail tracks to expand and buckle. More frequent and severe heat waves may require track repairs or speed restrictions to avoid derailments. Heavy precipitation could also lead to delays and disruption, and tropical storms and hurricanes can also flood or leave debris on railways, disrupting rail travel and freight transport. For example, the June 2008 Midwest floods closed major east-west rail lines for several days. Like roadways, coastal railways and subways are subject to inundation from sea level rise and storm surges. This is particularly true in underground pathways and tunnels, which are often already below sea level. For example, after Hurricane Sandy hit New York City and New Jersey subway and commuter rail systems with a 14-foot storm surge, millions of people were left without subway service for over a week in 2012. Damages from flooding may require rail lines and subway infrastructure to be rebuilt or raised in future expansion projects.
Improvements in traffic law enforcement can lead to rapid reductions in deaths and injuries. Requiring drivers to obey the speed limit, yield to pedestrians and cyclists, wear seatbelts, avoid drunk driving, and use child restraints can have a powerful impact on changing road user behavior. In New South Wales, Australia, a higher penalty for speeding offences by novice drivers resulted in a 30 percent reduction in the number of fatal crashes involving those drivers. From 2008 to 2012, seatbelts saved an estimated 63,000 lives in the United States, enough to fill 79 Airbus A380s. 2b1af7f3a8