They also ensure that pedestrians and bicycles have a distinct advantage by introducing exclusive shortcuts by path connections through blocks and parks, and are characterized by the removal of traditional traffic signals and signs, and even by the removal of the distinction between carriageway and foot-way (sidewalk), are also becoming increasingly popular. Both approaches can be shown to be effective. Such a principle of organization is referred to as "Filtered Permeability" implying a preferential treatment of active modes of transport. They show that four-way intersections combined with cut-through traffic are the most significant contributors to increased collisions.
These new patterns, which are recommended for laying out neighborhoods, are based on analyses of collision data of large regional districts and over extended periods. Most light poles are designed to break at the base rather than violently stop a car that hits them. Safety barriers can provide some combination of physical protection and visual protection depending on their environment. Modern safety barriers are designed to absorb impact energy and minimize the risk to the occupants of cars and bystanders. Physical protection is important for protecting sensitive building and pedestrian areas. Visual protection is necessary to alert drivers to changes in road patterns. For example, most side rails are now anchored to the ground, so that they cannot skewer a passenger compartment. Some road fixtures such as signs and fire hydrants are designed to collapse on impact. authorities have removed trees in the vicinity of roads; while the idea of "dangerous trees" has attracted a certain amount of skepticism.
These are just a few elements of highway engineering. In some cases, there are raised markers between lanes to reinforce the lane boundaries; these are often reflective. In pedestrian areas, speed bumps are often placed to slow cars, preventing them from going too fast near pedestrians. Most roads are cambered, that is, made so that they have rounded surfaces, to reduce standing water and ice, primarily to prevent frost damage but also increasing traction in poor weather. Some sections of road are now surfaced with porous bitumen to enhance drainage; this is particularly done on bends. Poor road surfaces can lead to safety problems. If too much asphalt or bituminous binder is used in asphalt concrete, the binder can 'bleed' or flush' to the surface, leaving a very smooth surface that provides little traction when wet.
As well as that, there are often grooves cut into the surface of cement highways to channel water away, and rumble strips at the edges of highways to rouse inattentive drivers with the loud noise they make when driven over. Either of these problems can increase wet-weather crashes by increasing braking distances or contributing to loss of control. If the pavement is insufficiently sloped or poorly drained, standing water on the surface can also lead to wet-weather crashes due to hydroplaning. Certain kinds of stone aggregate become very smooth or polished under the constant wearing action of vehicle tyres, again leading to poor wet-weather traction. Road hazards and intersections in some areas are now usually marked several times, roughly five, twenty, and sixty seconds in advance so that drivers are less likely to attempt violent manoeuvres.