ROAD SAFETY...

ROAD TRAFFIC SAFETY...

SIDEWALKS, CURBS AND TRAFFIC IN USA

Road traffic safety refers to methods and measures for reducing the risk of a person using the road network being killed or seriously injured. The users of a road include pedestrians, cyclists, motorists, their passengers, and passengers of on-road public transport, mainly buses and trams. Best-practice road safety strategies focus upon the prevention of serious injury and death crashes in spite of human fallibility^[1] (which is contrasted with the old road safety paradigm of simply reducing crashes assuming road user compliance with traffic regulations). Safe road design is now about providing a road environment which ensures vehicle speeds will be within the human tolerances for serious injury and death wherever conflict points exist.

safety traffic signals..

As sustainable solutions for all classes of road have not been identified, particularly lowly trafficked rural and remote roads, a hierarchy of control should be applied, similar to best practice Occupational Safety and Health. At the highest level is sustainable prevention of serious injury and death crashes, with sustainable requiring all key result areas to be considered. At the second level is real time risk reduction, which involves providing users at severe risk with a specific warning to enable them to take mitigating action. The third level is about reducing the crash risk which involves applying the road design standards and guidelines (such as from AASHTO), improving driver behaviour and enforcement.

The basic strategy of a Safe System approach is to ensure that in the event of a crash, the impact energies remain below the threshold likely to produce either death or serious injury. This threshold will vary from crash scenario to crash scenario, depending upon the level of protection offered to the road users involved. For example, the chances of survival for an unprotected pedestrian hit by a vehicle diminish rapidly at speeds greater than 30 km/h, whereas for a properly restrained motor vehicle occupant the critical impact speed is 50 km/h (for side impact crashes) and 70 km/h (for head-on crashe

Background

Road traffic crashes are one of the world’s largest public health and injury prevention problems. The problem is all the more acute because the victims are overwhelmingly healthy prior to their crashes. According to the World Health Organization (WHO), more than a million people are killed on the world’s roads each year. A report published by the WHO in 2004 estimated that some 1.2m people were killed and 50m injured in traffic collisions on the roads around the world each year and was the leading cause of death among children 10 – 19 years of age. The report also noted that the problem was most severe in developing countries and that simple prevention measures could halve the number of deaths.

pedestrian crossing and line marking of road

Built-up areas

a curb extension at the mid block

On existing neighborhood roads where many vulnerable road users, such as pedestrians and bicyclists can be found, traffic calming can be a tool for road safety. Though not strictly a traffic calming measure, mini-traffic circles implanted in existing, normal intersections of neighbourhood streets, have been shown to reduce collisions at intersections dramatically (see picture).Shared space schemes, which rely on human instincts and interactions, such as eye contact, for their effectiveness, and are characterised by the removal of traditional traffic signals and signs, and even by the removal of the distinction between carriageway (roadway) and footway (sidewalk), are also becoming increasingly popular. Both approaches can be shown to be effective.

For planned neighbourhoods, studies recommend new network configurations, such as the Fused Grid or 3-Way Offset. These layout models organize a neighbourhood area as a zone of no cut-through traffic by means of loops or dead-end streets. They also ensure that pedestrians and bicycles have a distinct advantage by introducing exclusive shortcuts by means of path connections through blocks and parks. Such a principle of organization is referred to as "Filtered Permeability" implying a preferential treatment of active modes of transport. These new patterns, which are recommended for laying out neighbourhoods, are based on analyses of collision data of large regional districts and over extended time periods.They show that four-way intersections combined with cut-through traffic are the most significant contributors to increased collisions.

traffic lights ።።

Turning across traffic።።።

Turning across traffic (i.e. turning left in right-hand drive countries, turning right in left-hand drive countries) poses several risks. The more serious risk is a collision with oncoming traffic. Since this is nearly a head-on collision injuries are common. It is the most common cause of fatalities in a built up area. The other risk is involvement in a rear-end collision while waiting for a gap in oncoming traffic.

Countermeasures for this type of collision include:

Addition of left turn lanes
Providing protected turn phasing at signalized intersections
Using indirect turn treatments such as the Michigan left
Converting conventional intersections to roundaboutsIn the absence of these facilities as a driver about to turn:

Keep your wheels straight, so that in the event of a rear end shunt, you are not pushed into on coming traffic.
When you think it is clear, look away, to the road that you are entering. There is an optical illusion that, after a time, presents an oncoming vehicle as further away, and travelling slower. Looking away breaks this illusion.

Reference:

^ Parslow,B and Wyvill, G Seeing in 3-D, course 42, SIGGRAPH 2001, Los Angeles

Turns across traffic have been shown to be problematic for older drivers.

Designing for pedestrians and cyclists።።።

Pedestrians and Cyclists are among the most vulnerable road users, and in some countries constitute over half of all road deaths. Interventions aimed at improving safety of non-motorised users:

Sidewalks of suitable width for the expected pedestrian traffic
pedestrian crossings close to the desire line which allow pedestrians to cross roads safely
segregated pedestrian routes and cycle lanes away from the main highway
Overbridges (tend to be unpopular with pedestrians and cyclists due to additional distance and effort)
Underpasses (these can pose heightened risk from crime is not designed well, can work for cyclists in some cases)
traffic calming and speed humps
low speed limits that are rigorous enforced, possibly by speed cameras
shared space schemes giving ownership of the road space and equal priority to all road users, regardless of mode of use
pedestrian barriers to prevent pedestrians crossing dangerous locations

Pedestrians' advocates question the equitability of schemes if they impose extra time and effort on the pedestrian to remain safe from vehicles, for example overbridges with long slopes or steps up and down, underpasses with steps and addition possible risk of crime and at-grade crossings off the desire line. The Make Roads Safe was criticised in 2007 for proposing such features. Successful pedestrian schemes tend to avoid over-bridges and underpasses and instead use at-grade crossings (such as pedestrian crossings) close the intended route. Successful cycling scheme by contrast avoid frequent stops even if some additional distance is involved given that the main effort required for cyclists is starting off.

In Costa Rica 57% of road deaths are pedestrians, however a partnership between AACR, Cosevi, MOPT and iRAP has proposed the construction of 190 km of pedestrian footpaths and 170 pedestrian crossings which could save over 9000 fatal or serious injuries over 20 years.

Major highways

Major highways including motorways, freeways, Autobahnen and Interstates are designed for safer high-speed operation and generally have lower levels of injury per vehicle km than other roads.

Safety features include:

limited access from properties and local roads.
Grade separated junctions
Median dividers between opposite-direction traffic to reduce likelihood of head-on collisions
Removing roadside obstacles.
Prohibition of more vulnerable road users and slower vehicles.
Placements of energy attenuation devices (e.g. guard rails, wide grassy areas, sand barrels).
Eliminating road toll booths

The ends of some guard rails on high-speed highways in the United States are protected with impact attenuators, designed to gradually absorb the kinetic energy of a vehicle and slow it more gently before it can strike the end of the guard rail head on, which would be devastating at high speed. Several mechanisms are used to dissipate the kinetic energy. Fitch Barriers, a system of sand-filled barrels, uses momentum transfer from the vehicle to the sand. Many other systems tear or deform steel members to absorb energy and gradually stop the vehicle.

In some countries major roads have "tone bands" impressed or cut into the edges of the legal roadway, so that drowsing drivers are awakened by a loud hum as they release the steering and drift off the edge of the road. Tone bands are also referred to as "rumble strips", owing to the sound they create. An alternative method is the use of "Raised Rib" markings, which consists of a continuous line marking with ribs across the line at regular intervals. They were first specially authorised for use on motorways as an edge line marking to separate the edge of the hard shoulder from the main carriageway. The objective of the marking is to achieve improved visual delineation of the carriageway edge in wet conditions at night. It also provides an audible/vibratory warning to vehicle drivers, should they stray from the carriageway, and run onto the marking.

Better motorways are banked on curves in order to reduce the need for tire-traction and increase stability for vehicles with high centers of gravity.

An example of the importance of roadside clear zones can be found on the Isle of Man TT motorcycle race course. It is much more dangerous than Silverstone because of the lack of runoff. When a rider falls off at Silverstone he slides along slowly losing energy, so minimal injuries. When he falls of in the Manx he impacts with trees and walls. Similarly, a clear zone alongside a freeway or other high speed road can prevent off-road excursions from becoming fixed-object crashes.

The U.S. has developed a prototype automated roadway, to reduce driver fatigue and increase the carrying capacity of the roadway. Roadside units participating in future Wireless vehicle safety communications networks have been studied.

Motorways are far more expensive and space-consumptive to build than ordinary roads, so are only used as principal arterial routes. In developed nations, motorways bear a significant portion of motorized travel; for example, the United Kingdom's 3533 km of motorways represented less than 1.5% of the United Kingdom's roadways in 2003, but carry 23% of road traffic.

The proportion of traffic borne by motorways is a significant safety factor. For example, even though the United Kingdom had a higher fatality rates on both motorways and non-motorways than Finland, both nations shared the same overall fatality rate in 2003. This result was due to the United Kingdom's higher proportion of motorway travel.

Similarly, the reduction of conflicts with other vehicles on motorways results in smoother traffic flow, reduced collision rates, and reduced fuel consumption compared with stop-and-go traffic on other roadways.

The improved safety and fuel economy of motorways are common justifications for building more motorways. However, the planned capacity of motorways is often exceeded in a shorter timeframe than initially planned, due to the under estimation of the extent of the suppressed demand for road travel. In developing nations, there is significant public debate on the desirability of continued investment in motorways.

Motorways around the world are subject to a broad range of speed limits. Recent experiments with variable speed limits based on automatic measurements of traffic density have delivered both improvements in traffic flow and reduced collision rates, based on principles of turbulent flow analysis.

With effect from January 2005 and based primarily on safety grounds, the UK’s Highways Agency's policy is that all new motorway schemes are to use high containment concrete step barriers in the central reserve. All existing motorways will introduce concrete barriers into the central reserve as part of ongoing upgrades and through replacement as and when these systems have reached the end of their useful life. This change of policy applies only to barriers in the central reserve of high speed roads and not to verge side barriers. Other routes will continue to use steel barriers.

More people die on the hard shoulder than on the highway itself. Without other vehicles passing a parked car, following drivers are unaware that the vehicle is parked, despite hazard lights. Truck drivers indicate that they are parked by putting their cab seat behind their truck. In the UK, the AA and police park their vehicles on the hard shoulder at a slight angle so that following drivers can see down the side of their vehicle and are therefore aware that they are stopped.

30% of highway crashes that occur in the vicinity of toll collection booths in the countries that have them, these can be reduced by switching to electronic toll systems.