Road safety considerations

almost for free, especially when site-selection criteria and safety measures are considered in upfront planning (van steenbergen 2017). • Roads in flood-prone areas may be built with lower embankments and equipped with controlled overflow “floodway” structures instead of high embankments (see chapter 7). This reduces costs enormously because the expenditure on the embankments is considerably less, and roads do not wash out in unpredictable locations. • Culvert-less, “nonvented” drifts may be used as road crossings. such drifts cost the same as road drifts with culverts but prevent the scouring of rivers and encourage the buildup of sand-water storage immediately upstream of the drift, effectively combining the function of a road crossing with that of a sand dam (neal 2012). Based on a calculation of costs and benefits, excellent development (2018) estimates that maintenance costs on culvert-less drifts are only 13 percent of the maintenance costs of vented drifts. • Water levels in the coastal lowlands, such as the polders in Bangladesh (see chapter 5), may be managed. The only option for doing so is to make use of the road network in these areas, expand it wisely, and equip it with appropriate cross-drainage structures. • Road embankments may be used for water storage, as in countries as diverse as Burkina faso, Portugal, Turkmenistan, Uganda, and the Republic of Yemen.

Because road embankments are a sunk cost, reservoirs can be developed with comparatively minimal additional expense. • Low-cost measures, such as drainage dips, water bars, and infiltration bunds, may be used on unpaved roads to guide water to productive uses and prevent the kind of damage to those roads that is usually not repaired (see chapter 10).

ROAD SAFETY CONSIDERATIONS

numerous issues must be carefully considered in the design, construction, and ongoing maintenance and rehabilitation of roads, many of which cannot be fully addressed in these guidelines. Road safety requirements are among the many issues that are not fully addressed but deserve mention.

Attention to the road context is a first-order principle in road safety. Certain environments call for lower vehicle operating speeds, whereas others can be adapted to mitigate some of the risks posed by higher operating speeds, enabling faster movement. In general terms, measures to reduce speed are necessary in villages and towns and in other contexts in which nonmotorized road users are frequently in close proximity to high-speed traffic. Higher travel speeds can be accommodated more easily in rural areas where these risk factors are not present. In these environments, roadside trees and structures pose significant and often underappreciated risks to vehicle occupants. Road-safety decision-making also requires proactive identification of risks. for instance, operation and maintenance of certain road-water management facilities may also introduce people to high-risk areas of the roadside.

In addition, motor vehicle operators often underestimate road-safety risks and overestimate their capacity to manage those risks. This overconfidence often results in higher and less safe operating speeds. for instance, removal of roadside objects may give vehicle operators a greater feeling of safety, resulting in higher speeds that are not suitable for the road surface conditions. Road user

psychology therefore adds significant complexity to the challenge of designing safer roads. Because the road user is unlikely to fully appreciate the risk posed by any individual safety deficiency in a given context, the road engineer must consider how all aspects of the road and roadside will affect safety.

Indeed, as a new awareness of what makes a road fit for safe travel has emerged among the road design profession internationally, much of the guidance that had informed past design standards has been questioned. substantial revision is taking place. This shift in thinking is reflected in the Un decade of Action 2011–2020 and the safe system approach, which emphasizes prevention of serious injuries and fatalities by building road infrastructure that is forgiving of road users’ mistakes. Preference is given to creating conditions that reduce the likelihood that a road user would make an error that could result in a serious collision. The new thinking also accepts that road user error will inevitably occur and strongly favors road designs that are forgiving so these errors are less likely to cause serious injury or death. examples include maintaining good shoulder conditions so that unintentional encroachment into the shoulder does not result in an immediate loss of control that could have unpredictable outcomes, and establishing a median barrier to prevent errant vehicles from crossing over the carriageway into oncoming traffic.

A complete summary of the safe system approach to providing safer road infrastructure is beyond the scope of these guidelines. However, many traditional approaches to the use and management of roads and roadsides have been found to reflect a lack of awareness of conditions that pose a risk to the lives of road users. The impact of these shortcomings on safety outcomes at the network level is often substantial.

Identification of risk factors for the crash types that are most likely to result in fatal and serious injury outcomes is vital to prevention. These guidelines highlight the most common types of fatal and serious injury crashes experienced on the world’s roads in the contexts that are the focus of this report. The most important collision risks in relation to existing and new roads in low- and middle-income country contexts fall into three categories.

• (a) Run off road crashes. Vehicles can hit fixed objects, including manmade roadside structures and trees—which may pose conflicts with the greening agenda. Vehicles may also encounter uneven roadside terrain and vertical or near-vertical drops at the roadside, such as dry ditches and ponds. Water bodies adjacent to the roadside might also be encountered. • (b) Unsafe waterflows over roads. It is vital to consider the consequences of unsafe water flows over roads and how to minimize loss of life in those circumstances. Roads that incorporate floodways must protect pedestrians and other nonmotorized road users as far as is possible from actual floodwater flows. Pedestrians and other nonmotorized road users traveling along or crossing roads in the vicinity of floodways are at a heightened risk of being involved in collisions with vehicles. It is often possible for motor vehicles to traverse floodwater flows that would easily sweep other road users into the current. • (c) Safe road operation during construction. Many road safety issues must be fully considered during construction of a road to ensure safe conditions for road users and road construction workers.